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Data model</a><ul> <li><a class="reference internal" href="#objects-values-and-types">3.1. Objects, values and types</a></li> <li><a class="reference internal" href="#the-standard-type-hierarchy">3.2. The standard type hierarchy</a><ul> <li><a class="reference internal" href="#none">3.2.1. None</a></li> <li><a class="reference internal" href="#notimplemented">3.2.2. NotImplemented</a></li> <li><a class="reference internal" href="#ellipsis">3.2.3. Ellipsis</a></li> <li><a class="reference internal" href="#numbers-number">3.2.4. <code class="xref py py-class docutils literal notranslate">numbers.Number</code></a><ul> <li><a class="reference internal" href="#numbers-integral">3.2.4.1. <code class="xref py py-class docutils literal notranslate">numbers.Integral</code></a></li> <li><a class="reference internal" href="#numbers-real-float">3.2.4.2. <code class="xref py py-class docutils literal notranslate">numbers.Real</code> (<code class="xref py py-class docutils literal notranslate">float</code>)</a></li> <li><a class="reference internal" href="#numbers-complex-complex">3.2.4.3. <code class="xref py py-class docutils literal notranslate">numbers.Complex</code> (<code class="xref py py-class docutils literal notranslate">complex</code>)</a></li> </ul> </li> <li><a class="reference internal" href="#sequences">3.2.5. Sequences</a><ul> <li><a class="reference internal" href="#immutable-sequences">3.2.5.1. Immutable sequences</a></li> <li><a class="reference internal" href="#mutable-sequences">3.2.5.2. Mutable sequences</a></li> </ul> </li> <li><a class="reference internal" href="#set-types">3.2.6. Set types</a></li> <li><a class="reference internal" href="#mappings">3.2.7. Mappings</a><ul> <li><a class="reference internal" href="#dictionaries">3.2.7.1. Dictionaries</a></li> </ul> </li> <li><a class="reference internal" href="#callable-types">3.2.8. Callable types</a><ul> <li><a class="reference internal" href="#user-defined-functions">3.2.8.1. User-defined functions</a><ul> <li><a class="reference internal" href="#special-read-only-attributes">3.2.8.1.1. Special read-only attributes</a><ul> <li><a class="reference internal" href="#function.__globals__"><code class="docutils literal notranslate">__globals__</code></a></li> <li><a class="reference internal" href="#function.__closure__"><code class="docutils literal notranslate">__closure__</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-writable-attributes">3.2.8.1.2. Special writable attributes</a><ul> <li><a class="reference internal" href="#function.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#function.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#function.__qualname__"><code class="docutils literal notranslate">__qualname__</code></a></li> <li><a class="reference internal" href="#function.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#function.__defaults__"><code class="docutils literal notranslate">__defaults__</code></a></li> <li><a class="reference internal" href="#function.__code__"><code class="docutils literal notranslate">__code__</code></a></li> <li><a class="reference internal" href="#function.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> <li><a class="reference internal" href="#function.__annotations__"><code class="docutils literal notranslate">__annotations__</code></a></li> <li><a class="reference internal" href="#function.__kwdefaults__"><code class="docutils literal notranslate">__kwdefaults__</code></a></li> <li><a class="reference internal" href="#function.__type_params__"><code class="docutils literal notranslate">__type_params__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#instance-methods">3.2.8.2. Instance methods</a><ul> <li><a class="reference internal" href="#method.__self__"><code class="docutils literal notranslate">__self__</code></a></li> <li><a class="reference internal" href="#method.__func__"><code class="docutils literal notranslate">__func__</code></a></li> <li><a class="reference internal" href="#method.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#method.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#method.__module__"><code class="docutils literal notranslate">__module__</code></a></li> </ul> </li> <li><a class="reference internal" href="#generator-functions">3.2.8.3. Generator functions</a></li> <li><a class="reference internal" href="#coroutine-functions">3.2.8.4. Coroutine functions</a></li> <li><a class="reference internal" href="#asynchronous-generator-functions">3.2.8.5. Asynchronous generator functions</a></li> <li><a class="reference internal" href="#built-in-functions">3.2.8.6. Built-in functions</a></li> <li><a class="reference internal" href="#built-in-methods">3.2.8.7. Built-in methods</a></li> <li><a class="reference internal" href="#classes">3.2.8.8. Classes</a></li> <li><a class="reference internal" href="#class-instances">3.2.8.9. Class Instances</a></li> </ul> </li> <li><a class="reference internal" href="#modules">3.2.9. Modules</a><ul> <li><a class="reference internal" href="#import-related-attributes-on-module-objects">3.2.9.1. Import-related attributes on module objects</a><ul> <li><a class="reference internal" href="#module.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#module.__spec__"><code class="docutils literal notranslate">__spec__</code></a></li> <li><a class="reference internal" href="#module.__package__"><code class="docutils literal notranslate">__package__</code></a></li> <li><a class="reference internal" href="#module.__loader__"><code class="docutils literal notranslate">__loader__</code></a></li> <li><a class="reference internal" href="#module.__path__"><code class="docutils literal notranslate">__path__</code></a></li> <li><a class="reference internal" href="#module.__file__"><code class="docutils literal notranslate">__file__</code></a></li> <li><a class="reference internal" href="#module.__cached__"><code class="docutils literal notranslate">__cached__</code></a></li> </ul> </li> <li><a class="reference internal" href="#other-writable-attributes-on-module-objects">3.2.9.2. Other writable attributes on module objects</a><ul> <li><a class="reference internal" href="#module.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#module.__annotations__"><code class="docutils literal notranslate">__annotations__</code></a></li> </ul> </li> <li><a class="reference internal" href="#module-dictionaries">3.2.9.3. Module dictionaries</a><ul> <li><a class="reference internal" href="#module.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#custom-classes">3.2.10. Custom classes</a><ul> <li><a class="reference internal" href="#special-attributes">3.2.10.1. Special attributes</a><ul> <li><a class="reference internal" href="#type.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#type.__qualname__"><code class="docutils literal notranslate">__qualname__</code></a></li> <li><a class="reference internal" href="#type.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#type.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> <li><a class="reference internal" href="#type.__bases__"><code class="docutils literal notranslate">__bases__</code></a></li> <li><a class="reference internal" href="#type.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#type.__annotations__"><code class="docutils literal notranslate">__annotations__</code></a></li> <li><a class="reference internal" href="#type.__type_params__"><code class="docutils literal notranslate">__type_params__</code></a></li> <li><a class="reference internal" href="#type.__static_attributes__"><code class="docutils literal notranslate">__static_attributes__</code></a></li> <li><a class="reference internal" href="#type.__firstlineno__"><code class="docutils literal notranslate">__firstlineno__</code></a></li> <li><a class="reference internal" href="#type.__mro__"><code class="docutils literal notranslate">__mro__</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-methods">3.2.10.2. Special methods</a><ul> <li><a class="reference internal" href="#type.mro"><code class="docutils literal notranslate">mro()</code></a></li> <li><a class="reference internal" href="#type.__subclasses__"><code class="docutils literal notranslate">__subclasses__()</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#id4">3.2.11. Class instances</a><ul> <li><a class="reference internal" href="#id5">3.2.11.1. Special attributes</a><ul> <li><a class="reference internal" href="#object.__class__"><code class="docutils literal notranslate">__class__</code></a></li> <li><a class="reference internal" href="#object.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#i-o-objects-also-known-as-file-objects">3.2.12. I/O objects (also known as file objects)</a></li> <li><a class="reference internal" href="#internal-types">3.2.13. Internal types</a><ul> <li><a class="reference internal" href="#code-objects">3.2.13.1. Code objects</a><ul> <li><a class="reference internal" href="#index-60">3.2.13.1.1. Special read-only attributes</a><ul> <li><a class="reference internal" href="#codeobject.co_name"><code class="docutils literal notranslate">co_name</code></a></li> <li><a class="reference internal" href="#codeobject.co_qualname"><code class="docutils literal notranslate">co_qualname</code></a></li> <li><a class="reference internal" href="#codeobject.co_argcount"><code class="docutils literal notranslate">co_argcount</code></a></li> <li><a class="reference internal" href="#codeobject.co_posonlyargcount"><code class="docutils literal notranslate">co_posonlyargcount</code></a></li> <li><a class="reference internal" href="#codeobject.co_kwonlyargcount"><code class="docutils literal notranslate">co_kwonlyargcount</code></a></li> <li><a class="reference internal" href="#codeobject.co_nlocals"><code class="docutils literal notranslate">co_nlocals</code></a></li> <li><a class="reference internal" href="#codeobject.co_varnames"><code class="docutils literal notranslate">co_varnames</code></a></li> <li><a class="reference internal" href="#codeobject.co_cellvars"><code class="docutils literal notranslate">co_cellvars</code></a></li> <li><a class="reference internal" href="#codeobject.co_freevars"><code class="docutils literal notranslate">co_freevars</code></a></li> <li><a class="reference internal" href="#codeobject.co_code"><code class="docutils literal notranslate">co_code</code></a></li> <li><a class="reference internal" href="#codeobject.co_consts"><code class="docutils literal notranslate">co_consts</code></a></li> <li><a class="reference internal" href="#codeobject.co_names"><code class="docutils literal notranslate">co_names</code></a></li> <li><a class="reference internal" href="#codeobject.co_filename"><code class="docutils literal notranslate">co_filename</code></a></li> <li><a class="reference internal" href="#codeobject.co_firstlineno"><code class="docutils literal notranslate">co_firstlineno</code></a></li> <li><a class="reference internal" href="#codeobject.co_lnotab"><code class="docutils literal notranslate">co_lnotab</code></a></li> <li><a class="reference internal" href="#codeobject.co_stacksize"><code class="docutils literal notranslate">co_stacksize</code></a></li> <li><a class="reference internal" href="#codeobject.co_flags"><code class="docutils literal notranslate">co_flags</code></a></li> </ul> </li> <li><a class="reference internal" href="#methods-on-code-objects">3.2.13.1.2. Methods on code objects</a><ul> <li><a class="reference internal" href="#codeobject.co_positions"><code class="docutils literal notranslate">co_positions()</code></a></li> <li><a class="reference internal" href="#codeobject.co_lines"><code class="docutils literal notranslate">co_lines()</code></a></li> <li><a class="reference internal" href="#codeobject.replace"><code class="docutils literal notranslate">replace()</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#frame-objects">3.2.13.2. Frame objects</a><ul> <li><a class="reference internal" href="#index-66">3.2.13.2.1. Special read-only attributes</a><ul> <li><a class="reference internal" href="#frame.f_back"><code class="docutils literal notranslate">f_back</code></a></li> <li><a class="reference internal" href="#frame.f_code"><code class="docutils literal notranslate">f_code</code></a></li> <li><a class="reference internal" href="#frame.f_locals"><code class="docutils literal notranslate">f_locals</code></a></li> <li><a class="reference internal" href="#frame.f_globals"><code class="docutils literal notranslate">f_globals</code></a></li> <li><a class="reference internal" href="#frame.f_builtins"><code class="docutils literal notranslate">f_builtins</code></a></li> <li><a class="reference internal" href="#frame.f_lasti"><code class="docutils literal notranslate">f_lasti</code></a></li> </ul> </li> <li><a class="reference internal" href="#index-67">3.2.13.2.2. Special writable attributes</a><ul> <li><a class="reference internal" href="#frame.f_trace"><code class="docutils literal notranslate">f_trace</code></a></li> <li><a class="reference internal" href="#frame.f_trace_lines"><code class="docutils literal notranslate">f_trace_lines</code></a></li> <li><a class="reference internal" href="#frame.f_trace_opcodes"><code class="docutils literal notranslate">f_trace_opcodes</code></a></li> <li><a class="reference internal" href="#frame.f_lineno"><code class="docutils literal notranslate">f_lineno</code></a></li> </ul> </li> <li><a class="reference internal" href="#frame-object-methods">3.2.13.2.3. Frame object methods</a><ul> <li><a class="reference internal" href="#frame.clear"><code class="docutils literal notranslate">clear()</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#traceback-objects">3.2.13.3. Traceback objects</a><ul> <li><a class="reference internal" href="#traceback.tb_frame"><code class="docutils literal notranslate">tb_frame</code></a></li> <li><a class="reference internal" href="#traceback.tb_lineno"><code class="docutils literal notranslate">tb_lineno</code></a></li> <li><a class="reference internal" href="#traceback.tb_lasti"><code class="docutils literal notranslate">tb_lasti</code></a></li> <li><a class="reference internal" href="#traceback.tb_next"><code class="docutils literal notranslate">tb_next</code></a></li> </ul> </li> <li><a class="reference internal" href="#slice-objects">3.2.13.4. Slice objects</a><ul> <li><a class="reference internal" href="#slice.indices"><code class="docutils literal notranslate">indices()</code></a></li> </ul> </li> <li><a class="reference internal" href="#static-method-objects">3.2.13.5. Static method objects</a></li> <li><a class="reference internal" href="#class-method-objects">3.2.13.6. Class method objects</a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#special-method-names">3.3. Special method names</a><ul> <li><a class="reference internal" href="#basic-customization">3.3.1. Basic customization</a><ul> <li><a class="reference internal" href="#object.__new__"><code class="docutils literal notranslate">__new__()</code></a></li> <li><a class="reference internal" href="#object.__init__"><code class="docutils literal notranslate">__init__()</code></a></li> <li><a class="reference internal" href="#object.__del__"><code class="docutils literal notranslate">__del__()</code></a></li> <li><a class="reference internal" href="#object.__repr__"><code class="docutils literal notranslate">__repr__()</code></a></li> <li><a class="reference internal" href="#object.__str__"><code class="docutils literal notranslate">__str__()</code></a></li> <li><a class="reference internal" href="#object.__bytes__"><code class="docutils literal notranslate">__bytes__()</code></a></li> <li><a class="reference internal" href="#object.__format__"><code class="docutils literal notranslate">__format__()</code></a></li> <li><a class="reference internal" href="#object.__lt__"><code class="docutils literal notranslate">__lt__()</code></a></li> <li><a class="reference internal" href="#object.__le__"><code class="docutils literal notranslate">__le__()</code></a></li> <li><a class="reference internal" href="#object.__eq__"><code class="docutils literal notranslate">__eq__()</code></a></li> <li><a class="reference internal" href="#object.__ne__"><code class="docutils literal notranslate">__ne__()</code></a></li> <li><a class="reference internal" href="#object.__gt__"><code class="docutils literal notranslate">__gt__()</code></a></li> <li><a class="reference internal" href="#object.__ge__"><code class="docutils literal notranslate">__ge__()</code></a></li> <li><a class="reference internal" href="#object.__hash__"><code class="docutils literal notranslate">__hash__()</code></a></li> <li><a class="reference internal" href="#object.__bool__"><code class="docutils literal notranslate">__bool__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#customizing-attribute-access">3.3.2. Customizing attribute access</a><ul> <li><a class="reference internal" href="#object.__getattr__"><code class="docutils literal notranslate">__getattr__()</code></a></li> <li><a class="reference internal" href="#object.__getattribute__"><code class="docutils literal notranslate">__getattribute__()</code></a></li> <li><a class="reference internal" href="#object.__setattr__"><code class="docutils literal notranslate">__setattr__()</code></a></li> <li><a class="reference internal" href="#object.__delattr__"><code class="docutils literal notranslate">__delattr__()</code></a></li> <li><a class="reference internal" href="#object.__dir__"><code class="docutils literal notranslate">__dir__()</code></a></li> <li><a class="reference internal" href="#customizing-module-attribute-access">3.3.2.1. Customizing module attribute access</a></li> <li><a class="reference internal" href="#implementing-descriptors">3.3.2.2. Implementing Descriptors</a><ul> <li><a class="reference internal" href="#object.__get__"><code class="docutils literal notranslate">__get__()</code></a></li> <li><a class="reference internal" href="#object.__set__"><code class="docutils literal notranslate">__set__()</code></a></li> <li><a class="reference internal" href="#object.__delete__"><code class="docutils literal notranslate">__delete__()</code></a></li> <li><a class="reference internal" href="#object.__objclass__"><code class="docutils literal notranslate">__objclass__</code></a></li> </ul> </li> <li><a class="reference internal" href="#invoking-descriptors">3.3.2.3. Invoking Descriptors</a></li> <li><a class="reference internal" href="#slots">3.3.2.4. __slots__</a><ul> <li><a class="reference internal" href="#object.__slots__"><code class="docutils literal notranslate">__slots__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#customizing-class-creation">3.3.3. Customizing class creation</a><ul> <li><a class="reference internal" href="#object.__init_subclass__"><code class="docutils literal notranslate">__init_subclass__()</code></a></li> <li><a class="reference internal" href="#object.__set_name__"><code class="docutils literal notranslate">__set_name__()</code></a></li> <li><a class="reference internal" href="#metaclasses">3.3.3.1. Metaclasses</a></li> <li><a class="reference internal" href="#resolving-mro-entries">3.3.3.2. Resolving MRO entries</a><ul> <li><a class="reference internal" href="#object.__mro_entries__"><code class="docutils literal notranslate">__mro_entries__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#determining-the-appropriate-metaclass">3.3.3.3. Determining the appropriate metaclass</a></li> <li><a class="reference internal" href="#preparing-the-class-namespace">3.3.3.4. Preparing the class namespace</a></li> <li><a class="reference internal" href="#executing-the-class-body">3.3.3.5. Executing the class body</a></li> <li><a class="reference internal" href="#creating-the-class-object">3.3.3.6. Creating the class object</a></li> <li><a class="reference internal" href="#uses-for-metaclasses">3.3.3.7. Uses for metaclasses</a></li> </ul> </li> <li><a class="reference internal" href="#customizing-instance-and-subclass-checks">3.3.4. Customizing instance and subclass checks</a><ul> <li><a class="reference internal" href="#type.__instancecheck__"><code class="docutils literal notranslate">__instancecheck__()</code></a></li> <li><a class="reference internal" href="#type.__subclasscheck__"><code class="docutils literal notranslate">__subclasscheck__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-generic-types">3.3.5. Emulating generic types</a><ul> <li><a class="reference internal" href="#object.__class_getitem__"><code class="docutils literal notranslate">__class_getitem__()</code></a></li> <li><a class="reference internal" href="#the-purpose-of-class-getitem">3.3.5.1. The purpose of __class_getitem__</a></li> <li><a class="reference internal" href="#class-getitem-versus-getitem">3.3.5.2. __class_getitem__ versus __getitem__</a></li> </ul> </li> <li><a class="reference internal" href="#emulating-callable-objects">3.3.6. Emulating callable objects</a><ul> <li><a class="reference internal" href="#object.__call__"><code class="docutils literal notranslate">__call__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-container-types">3.3.7. Emulating container types</a><ul> <li><a class="reference internal" href="#object.__len__"><code class="docutils literal notranslate">__len__()</code></a></li> <li><a class="reference internal" href="#object.__length_hint__"><code class="docutils literal notranslate">__length_hint__()</code></a></li> <li><a class="reference internal" href="#object.__getitem__"><code class="docutils literal notranslate">__getitem__()</code></a></li> <li><a class="reference internal" href="#object.__setitem__"><code class="docutils literal notranslate">__setitem__()</code></a></li> <li><a class="reference internal" href="#object.__delitem__"><code class="docutils literal notranslate">__delitem__()</code></a></li> <li><a class="reference internal" href="#object.__missing__"><code class="docutils literal notranslate">__missing__()</code></a></li> <li><a class="reference internal" href="#object.__iter__"><code class="docutils literal notranslate">__iter__()</code></a></li> <li><a class="reference internal" href="#object.__reversed__"><code class="docutils literal notranslate">__reversed__()</code></a></li> <li><a class="reference internal" href="#object.__contains__"><code class="docutils literal notranslate">__contains__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-numeric-types">3.3.8. Emulating numeric types</a><ul> <li><a class="reference internal" href="#object.__add__"><code class="docutils literal notranslate">__add__()</code></a></li> <li><a class="reference internal" href="#object.__sub__"><code class="docutils literal notranslate">__sub__()</code></a></li> <li><a class="reference internal" href="#object.__mul__"><code class="docutils literal notranslate">__mul__()</code></a></li> <li><a class="reference internal" href="#object.__matmul__"><code class="docutils literal notranslate">__matmul__()</code></a></li> <li><a class="reference internal" href="#object.__truediv__"><code class="docutils literal notranslate">__truediv__()</code></a></li> <li><a class="reference internal" href="#object.__floordiv__"><code class="docutils literal notranslate">__floordiv__()</code></a></li> <li><a class="reference internal" href="#object.__mod__"><code class="docutils literal notranslate">__mod__()</code></a></li> <li><a class="reference internal" href="#object.__divmod__"><code class="docutils literal notranslate">__divmod__()</code></a></li> <li><a class="reference internal" href="#object.__pow__"><code class="docutils literal notranslate">__pow__()</code></a></li> <li><a class="reference internal" href="#object.__lshift__"><code class="docutils literal notranslate">__lshift__()</code></a></li> <li><a class="reference internal" href="#object.__rshift__"><code class="docutils literal notranslate">__rshift__()</code></a></li> <li><a class="reference internal" href="#object.__and__"><code class="docutils literal notranslate">__and__()</code></a></li> <li><a class="reference internal" href="#object.__xor__"><code class="docutils literal notranslate">__xor__()</code></a></li> <li><a class="reference internal" href="#object.__or__"><code class="docutils literal notranslate">__or__()</code></a></li> <li><a class="reference internal" href="#object.__radd__"><code class="docutils literal notranslate">__radd__()</code></a></li> <li><a class="reference internal" href="#object.__rsub__"><code class="docutils literal notranslate">__rsub__()</code></a></li> <li><a class="reference internal" href="#object.__rmul__"><code class="docutils literal notranslate">__rmul__()</code></a></li> <li><a class="reference internal" href="#object.__rmatmul__"><code class="docutils literal notranslate">__rmatmul__()</code></a></li> <li><a class="reference internal" href="#object.__rtruediv__"><code class="docutils literal notranslate">__rtruediv__()</code></a></li> <li><a class="reference internal" href="#object.__rfloordiv__"><code class="docutils literal notranslate">__rfloordiv__()</code></a></li> <li><a class="reference internal" href="#object.__rmod__"><code class="docutils literal notranslate">__rmod__()</code></a></li> <li><a class="reference internal" href="#object.__rdivmod__"><code class="docutils literal notranslate">__rdivmod__()</code></a></li> <li><a class="reference internal" href="#object.__rpow__"><code class="docutils literal notranslate">__rpow__()</code></a></li> <li><a class="reference internal" href="#object.__rlshift__"><code class="docutils literal notranslate">__rlshift__()</code></a></li> <li><a class="reference internal" href="#object.__rrshift__"><code class="docutils literal notranslate">__rrshift__()</code></a></li> <li><a class="reference internal" href="#object.__rand__"><code class="docutils literal notranslate">__rand__()</code></a></li> <li><a class="reference internal" href="#object.__rxor__"><code class="docutils literal notranslate">__rxor__()</code></a></li> <li><a class="reference internal" href="#object.__ror__"><code class="docutils literal notranslate">__ror__()</code></a></li> <li><a class="reference internal" href="#object.__iadd__"><code class="docutils literal notranslate">__iadd__()</code></a></li> <li><a class="reference internal" href="#object.__isub__"><code class="docutils literal notranslate">__isub__()</code></a></li> <li><a class="reference internal" href="#object.__imul__"><code class="docutils literal notranslate">__imul__()</code></a></li> <li><a class="reference internal" href="#object.__imatmul__"><code class="docutils literal notranslate">__imatmul__()</code></a></li> <li><a class="reference internal" href="#object.__itruediv__"><code class="docutils literal notranslate">__itruediv__()</code></a></li> <li><a class="reference internal" href="#object.__ifloordiv__"><code class="docutils literal notranslate">__ifloordiv__()</code></a></li> <li><a class="reference internal" href="#object.__imod__"><code class="docutils literal notranslate">__imod__()</code></a></li> <li><a class="reference internal" href="#object.__ipow__"><code class="docutils literal notranslate">__ipow__()</code></a></li> <li><a class="reference internal" href="#object.__ilshift__"><code class="docutils literal notranslate">__ilshift__()</code></a></li> <li><a class="reference internal" href="#object.__irshift__"><code class="docutils literal notranslate">__irshift__()</code></a></li> <li><a class="reference internal" href="#object.__iand__"><code class="docutils literal notranslate">__iand__()</code></a></li> <li><a class="reference internal" href="#object.__ixor__"><code class="docutils literal notranslate">__ixor__()</code></a></li> <li><a class="reference internal" href="#object.__ior__"><code class="docutils literal notranslate">__ior__()</code></a></li> <li><a class="reference internal" href="#object.__neg__"><code class="docutils literal notranslate">__neg__()</code></a></li> <li><a class="reference internal" href="#object.__pos__"><code class="docutils literal notranslate">__pos__()</code></a></li> <li><a class="reference internal" href="#object.__abs__"><code class="docutils literal notranslate">__abs__()</code></a></li> <li><a class="reference internal" href="#object.__invert__"><code class="docutils literal notranslate">__invert__()</code></a></li> <li><a class="reference internal" href="#object.__complex__"><code class="docutils literal notranslate">__complex__()</code></a></li> <li><a class="reference internal" href="#object.__int__"><code class="docutils literal notranslate">__int__()</code></a></li> <li><a class="reference internal" href="#object.__float__"><code class="docutils literal notranslate">__float__()</code></a></li> <li><a class="reference internal" href="#object.__index__"><code class="docutils literal notranslate">__index__()</code></a></li> <li><a class="reference internal" href="#object.__round__"><code class="docutils literal notranslate">__round__()</code></a></li> <li><a class="reference internal" href="#object.__trunc__"><code class="docutils literal notranslate">__trunc__()</code></a></li> <li><a class="reference internal" href="#object.__floor__"><code class="docutils literal notranslate">__floor__()</code></a></li> <li><a class="reference internal" href="#object.__ceil__"><code class="docutils literal notranslate">__ceil__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#with-statement-context-managers">3.3.9. With Statement Context Managers</a><ul> <li><a class="reference internal" href="#object.__enter__"><code class="docutils literal notranslate">__enter__()</code></a></li> <li><a class="reference internal" href="#object.__exit__"><code class="docutils literal notranslate">__exit__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#customizing-positional-arguments-in-class-pattern-matching">3.3.10. Customizing positional arguments in class pattern matching</a><ul> <li><a class="reference internal" href="#object.__match_args__"><code class="docutils literal notranslate">__match_args__</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-buffer-types">3.3.11. Emulating buffer types</a><ul> <li><a class="reference internal" href="#object.__buffer__"><code class="docutils literal notranslate">__buffer__()</code></a></li> <li><a class="reference internal" href="#object.__release_buffer__"><code class="docutils literal notranslate">__release_buffer__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-method-lookup">3.3.12. Special method lookup</a></li> </ul> </li> <li><a class="reference internal" href="#coroutines">3.4. Coroutines</a><ul> <li><a class="reference internal" href="#awaitable-objects">3.4.1. Awaitable Objects</a><ul> <li><a class="reference internal" href="#object.__await__"><code class="docutils literal notranslate">__await__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#coroutine-objects">3.4.2. Coroutine Objects</a><ul> <li><a class="reference internal" href="#coroutine.send"><code class="docutils literal notranslate">send()</code></a></li> <li><a class="reference internal" href="#coroutine.throw"><code class="docutils literal notranslate">throw()</code></a></li> <li><a class="reference internal" href="#coroutine.close"><code class="docutils literal notranslate">close()</code></a></li> </ul> </li> <li><a class="reference internal" href="#asynchronous-iterators">3.4.3. Asynchronous Iterators</a><ul> <li><a class="reference internal" href="#object.__aiter__"><code class="docutils literal notranslate">__aiter__()</code></a></li> <li><a class="reference internal" href="#object.__anext__"><code class="docutils literal notranslate">__anext__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#asynchronous-context-managers">3.4.4. Asynchronous Context Managers</a><ul> <li><a class="reference internal" href="#object.__aenter__"><code class="docutils literal notranslate">__aenter__()</code></a></li> <li><a class="reference internal" href="#object.__aexit__"><code class="docutils literal notranslate">__aexit__()</code></a></li> </ul> </li> </ul> </li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="lexical_analysis.html" title="previous chapter">2. Lexical analysis</a> </div> <div> <h4>Next topic</h4> <a href="executionmodel.html" title="next chapter">4. Execution model</a> </div> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/main/Doc/reference/datamodel.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </nav> </div> </div> <div class="related" role="navigation" aria-label="Related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="executionmodel.html" title="4. Execution model" accesskey="N">next</a> |</li> <li class="right" > <a href="lexical_analysis.html" title="2. Lexical analysis" accesskey="P">previous</a> |</li> <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.13.0 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">The Python Language Reference</a> »</li> <li class="nav-item nav-item-this"><a href="">3. Data model</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="data-model"> <h1>3. Data model<a class="headerlink" href="#data-model" title="Link to this heading">¶</a></h1> <section id="objects-values-and-types"> <h2>3.1. Objects, values and types<a class="headerlink" href="#objects-values-and-types" title="Link to this heading">¶</a></h2> Objects are Python’s abstraction for data. All data in a Python program is represented by objects or by relations between objects. (In a sense, and in conformance to Von Neumann’s model of a “stored program computer”, code is also represented by objects.) Every object has an identity, a type and a value. An object’s identity never changes once it has been created; you may think of it as the object’s address in memory. The <a class="reference internal" href="expressions.html#is"><code class="xref std std-keyword docutils literal notranslate">is</code></a> operator compares the identity of two objects; the <a class="reference internal" href="../library/functions.html#id" title="id"><code class="xref py py-func docutils literal notranslate">id()</code></a> function returns an integer representing its identity. <div class="impl-detail compound"> CPython implementation detail: For CPython, <code class="docutils literal notranslate">id(x)</code> is the memory address where <code class="docutils literal notranslate">x</code> is stored. </div> An object’s type determines the operations that the object supports (e.g., “does it have a length?”) and also defines the possible values for objects of that type. The <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-func docutils literal notranslate">type()</code></a> function returns an object’s type (which is an object itself). Like its identity, an object’s type is also unchangeable. <a class="footnote-reference brackets" href="#id19" id="id1" role="doc-noteref">[1]</a> The value of some objects can change. Objects whose value can change are said to be mutable; objects whose value is unchangeable once they are created are called immutable. (The value of an immutable container object that contains a reference to a mutable object can change when the latter’s value is changed; however the container is still considered immutable, because the collection of objects it contains cannot be changed. So, immutability is not strictly the same as having an unchangeable value, it is more subtle.) An object’s mutability is determined by its type; for instance, numbers, strings and tuples are immutable, while dictionaries and lists are mutable. Objects are never explicitly destroyed; however, when they become unreachable they may be garbage-collected. An implementation is allowed to postpone garbage collection or omit it altogether — it is a matter of implementation quality how garbage collection is implemented, as long as no objects are collected that are still reachable. <div class="impl-detail compound"> CPython implementation detail: CPython currently uses a reference-counting scheme with (optional) delayed detection of cyclically linked garbage, which collects most objects as soon as they become unreachable, but is not guaranteed to collect garbage containing circular references. See the documentation of the <a class="reference internal" href="../library/gc.html#module-gc" title="gc: Interface to the cycle-detecting garbage collector."><code class="xref py py-mod docutils literal notranslate">gc</code></a> module for information on controlling the collection of cyclic garbage. Other implementations act differently and CPython may change. Do not depend on immediate finalization of objects when they become unreachable (so you should always close files explicitly). </div> Note that the use of the implementation’s tracing or debugging facilities may keep objects alive that would normally be collectable. Also note that catching an exception with a <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate">try</code></a>…<a class="reference internal" href="compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate">except</code></a> statement may keep objects alive. Some objects contain references to “external” resources such as open files or windows. It is understood that these resources are freed when the object is garbage-collected, but since garbage collection is not guaranteed to happen, such objects also provide an explicit way to release the external resource, usually a <code class="xref py py-meth docutils literal notranslate">close()</code> method. Programs are strongly recommended to explicitly close such objects. The <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate">try</code></a>…<a class="reference internal" href="compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate">finally</code></a> statement and the <a class="reference internal" href="compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement provide convenient ways to do this. Some objects contain references to other objects; these are called containers. Examples of containers are tuples, lists and dictionaries. The references are part of a container’s value. In most cases, when we talk about the value of a container, we imply the values, not the identities of the contained objects; however, when we talk about the mutability of a container, only the identities of the immediately contained objects are implied. So, if an immutable container (like a tuple) contains a reference to a mutable object, its value changes if that mutable object is changed. Types affect almost all aspects of object behavior. Even the importance of object identity is affected in some sense: for immutable types, operations that compute new values may actually return a reference to any existing object with the same type and value, while for mutable objects this is not allowed. For example, after <code class="docutils literal notranslate">a = 1; b = 1</code>, a and b may or may not refer to the same object with the value one, depending on the implementation. This is because <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> is an immutable type, so the reference to <code class="docutils literal notranslate">1</code> can be reused. This behaviour depends on the implementation used, so should not be relied upon, but is something to be aware of when making use of object identity tests. However, after <code class="docutils literal notranslate">c = []; d = []</code>, c and d are guaranteed to refer to two different, unique, newly created empty lists. (Note that <code class="docutils literal notranslate">e = f = []</code> assigns the same object to both e and f.) </section> <section id="the-standard-type-hierarchy"> <h2>3.2. The standard type hierarchy<a class="headerlink" href="#the-standard-type-hierarchy" title="Link to this heading">¶</a></h2> Below is a list of the types that are built into Python. Extension modules (written in C, Java, or other languages, depending on the implementation) can define additional types. Future versions of Python may add types to the type hierarchy (e.g., rational numbers, efficiently stored arrays of integers, etc.), although such additions will often be provided via the standard library instead. Some of the type descriptions below contain a paragraph listing ‘special attributes.’ These are attributes that provide access to the implementation and are not intended for general use. Their definition may change in the future. <section id="none"> <h3>3.2.1. None<a class="headerlink" href="#none" title="Link to this heading">¶</a></h3> This type has a single value. There is a single object with this value. This object is accessed through the built-in name <code class="docutils literal notranslate">None</code>. It is used to signify the absence of a value in many situations, e.g., it is returned from functions that don’t explicitly return anything. Its truth value is false. </section> <section id="notimplemented"> <h3>3.2.2. NotImplemented<a class="headerlink" href="#notimplemented" title="Link to this heading">¶</a></h3> This type has a single value. There is a single object with this value. This object is accessed through the built-in name <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>. Numeric methods and rich comparison methods should return this value if they do not implement the operation for the operands provided. (The interpreter will then try the reflected operation, or some other fallback, depending on the operator.) It should not be evaluated in a boolean context. See <a class="reference internal" href="../library/numbers.html#implementing-the-arithmetic-operations">Implementing the arithmetic operations</a> for more details. <div class="versionchanged"> Changed in version 3.9: Evaluating <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a> in a boolean context is deprecated. While it currently evaluates as true, it will emit a <a class="reference internal" href="../library/exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a>. It will raise a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> in a future version of Python. </div> </section> <section id="ellipsis"> <h3>3.2.3. Ellipsis<a class="headerlink" href="#ellipsis" title="Link to this heading">¶</a></h3> This type has a single value. There is a single object with this value. This object is accessed through the literal <code class="docutils literal notranslate">...</code> or the built-in name <code class="docutils literal notranslate">Ellipsis</code>. Its truth value is true. </section> <section id="numbers-number"> <h3>3.2.4. <a class="reference internal" href="../library/numbers.html#numbers.Number" title="numbers.Number"><code class="xref py py-class docutils literal notranslate">numbers.Number</code></a><a class="headerlink" href="#numbers-number" title="Link to this heading">¶</a></h3> These are created by numeric literals and returned as results by arithmetic operators and arithmetic built-in functions. Numeric objects are immutable; once created their value never changes. Python numbers are of course strongly related to mathematical numbers, but subject to the limitations of numerical representation in computers. The string representations of the numeric classes, computed by <a class="reference internal" href="#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate">__repr__()</code></a> and <a class="reference internal" href="#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate">__str__()</code></a>, have the following properties: <ul class="simple"> <li>They are valid numeric literals which, when passed to their class constructor, produce an object having the value of the original numeric.</li> <li>The representation is in base 10, when possible.</li> <li>Leading zeros, possibly excepting a single zero before a decimal point, are not shown.</li> <li>Trailing zeros, possibly excepting a single zero after a decimal point, are not shown.</li> <li>A sign is shown only when the number is negative.</li> </ul> Python distinguishes between integers, floating-point numbers, and complex numbers: <section id="numbers-integral"> <h4>3.2.4.1. <a class="reference internal" href="../library/numbers.html#numbers.Integral" title="numbers.Integral"><code class="xref py py-class docutils literal notranslate">numbers.Integral</code></a><a class="headerlink" href="#numbers-integral" title="Link to this heading">¶</a></h4> These represent elements from the mathematical set of integers (positive and negative). <div class="admonition note"> Note The rules for integer representation are intended to give the most meaningful interpretation of shift and mask operations involving negative integers. </div> There are two types of integers: <dl> <dt>Integers (<a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>)</dt><dd>These represent numbers in an unlimited range, subject to available (virtual) memory only. For the purpose of shift and mask operations, a binary representation is assumed, and negative numbers are represented in a variant of 2’s complement which gives the illusion of an infinite string of sign bits extending to the left. </dd> <dt>Booleans (<a class="reference internal" href="../library/functions.html#bool" title="bool"><code class="xref py py-class docutils literal notranslate">bool</code></a>)</dt><dd>These represent the truth values False and True. The two objects representing the values <code class="docutils literal notranslate">False</code> and <code class="docutils literal notranslate">True</code> are the only Boolean objects. The Boolean type is a subtype of the integer type, and Boolean values behave like the values 0 and 1, respectively, in almost all contexts, the exception being that when converted to a string, the strings <code class="docutils literal notranslate">"False"</code> or <code class="docutils literal notranslate">"True"</code> are returned, respectively. </dd> </dl> </section> <section id="numbers-real-float"> <h4>3.2.4.2. <a class="reference internal" href="../library/numbers.html#numbers.Real" title="numbers.Real"><code class="xref py py-class docutils literal notranslate">numbers.Real</code></a> (<a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a>)<a class="headerlink" href="#numbers-real-float" title="Link to this heading">¶</a></h4> These represent machine-level double precision floating-point numbers. You are at the mercy of the underlying machine architecture (and C or Java implementation) for the accepted range and handling of overflow. Python does not support single-precision floating-point numbers; the savings in processor and memory usage that are usually the reason for using these are dwarfed by the overhead of using objects in Python, so there is no reason to complicate the language with two kinds of floating-point numbers. </section> <section id="numbers-complex-complex"> <h4>3.2.4.3. <a class="reference internal" href="../library/numbers.html#numbers.Complex" title="numbers.Complex"><code class="xref py py-class docutils literal notranslate">numbers.Complex</code></a> (<a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate">complex</code></a>)<a class="headerlink" href="#numbers-complex-complex" title="Link to this heading">¶</a></h4> These represent complex numbers as a pair of machine-level double precision floating-point numbers. The same caveats apply as for floating-point numbers. The real and imaginary parts of a complex number <code class="docutils literal notranslate">z</code> can be retrieved through the read-only attributes <code class="docutils literal notranslate">z.real</code> and <code class="docutils literal notranslate">z.imag</code>. </section> </section> <section id="sequences"> <h3>3.2.5. Sequences<a class="headerlink" href="#sequences" title="Link to this heading">¶</a></h3> These represent finite ordered sets indexed by non-negative numbers. The built-in function <a class="reference internal" href="../library/functions.html#len" title="len"><code class="xref py py-func docutils literal notranslate">len()</code></a> returns the number of items of a sequence. When the length of a sequence is n, the index set contains the numbers 0, 1, …, n-1. Item i of sequence a is selected by <code class="docutils literal notranslate">a[i]</code>. Some sequences, including built-in sequences, interpret negative subscripts by adding the sequence length. For example, <code class="docutils literal notranslate">a[-2]</code> equals <code class="docutils literal notranslate">a[n-2]</code>, the second to last item of sequence a with length <code class="docutils literal notranslate">n</code>. Sequences also support slicing: <code class="docutils literal notranslate">a[i:j]</code> selects all items with index k such that i <code class="docutils literal notranslate"><=</code> k <code class="docutils literal notranslate"><</code> j. When used as an expression, a slice is a sequence of the same type. The comment above about negative indexes also applies to negative slice positions. Some sequences also support “extended slicing” with a third “step” parameter: <code class="docutils literal notranslate">a[i:j:k]</code> selects all items of a with index x where <code class="docutils literal notranslate">x = i + n*k</code>, n <code class="docutils literal notranslate">>=</code> <code class="docutils literal notranslate">0</code> and i <code class="docutils literal notranslate"><=</code> x <code class="docutils literal notranslate"><</code> j. Sequences are distinguished according to their mutability: <section id="immutable-sequences"> <h4>3.2.5.1. Immutable sequences<a class="headerlink" href="#immutable-sequences" title="Link to this heading">¶</a></h4> An object of an immutable sequence type cannot change once it is created. (If the object contains references to other objects, these other objects may be mutable and may be changed; however, the collection of objects directly referenced by an immutable object cannot change.) The following types are immutable sequences: <dl id="index-18"> <dt>Strings</dt><dd>A string is a sequence of values that represent Unicode code points. All the code points in the range <code class="docutils literal notranslate">U+0000 - U+10FFFF</code> can be represented in a string. Python doesn’t have a char type; instead, every code point in the string is represented as a string object with length <code class="docutils literal notranslate">1</code>. The built-in function <a class="reference internal" href="../library/functions.html#ord" title="ord"><code class="xref py py-func docutils literal notranslate">ord()</code></a> converts a code point from its string form to an integer in the range <code class="docutils literal notranslate">0 - 10FFFF</code>; <a class="reference internal" href="../library/functions.html#chr" title="chr"><code class="xref py py-func docutils literal notranslate">chr()</code></a> converts an integer in the range <code class="docutils literal notranslate">0 - 10FFFF</code> to the corresponding length <code class="docutils literal notranslate">1</code> string object. <a class="reference internal" href="../library/stdtypes.html#str.encode" title="str.encode"><code class="xref py py-meth docutils literal notranslate">str.encode()</code></a> can be used to convert a <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> to <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> using the given text encoding, and <a class="reference internal" href="../library/stdtypes.html#bytes.decode" title="bytes.decode"><code class="xref py py-meth docutils literal notranslate">bytes.decode()</code></a> can be used to achieve the opposite. </dd> <dt>Tuples</dt><dd>The items of a tuple are arbitrary Python objects. Tuples of two or more items are formed by comma-separated lists of expressions. A tuple of one item (a ‘singleton’) can be formed by affixing a comma to an expression (an expression by itself does not create a tuple, since parentheses must be usable for grouping of expressions). An empty tuple can be formed by an empty pair of parentheses. </dd> <dt>Bytes</dt><dd>A bytes object is an immutable array. The items are 8-bit bytes, represented by integers in the range 0 <= x < 256. Bytes literals (like <code class="docutils literal notranslate">b'abc'</code>) and the built-in <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-func docutils literal notranslate">bytes()</code></a> constructor can be used to create bytes objects. Also, bytes objects can be decoded to strings via the <a class="reference internal" href="../library/stdtypes.html#bytes.decode" title="bytes.decode"><code class="xref py py-meth docutils literal notranslate">decode()</code></a> method. </dd> </dl> </section> <section id="mutable-sequences"> <h4>3.2.5.2. Mutable sequences<a class="headerlink" href="#mutable-sequences" title="Link to this heading">¶</a></h4> Mutable sequences can be changed after they are created. The subscription and slicing notations can be used as the target of assignment and <a class="reference internal" href="simple_stmts.html#del"><code class="xref std std-keyword docutils literal notranslate">del</code></a> (delete) statements. <div class="admonition note"> Note The <a class="reference internal" href="../library/collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate">collections</code></a> and <a class="reference internal" href="../library/array.html#module-array" title="array: Space efficient arrays of uniformly typed numeric values."><code class="xref py py-mod docutils literal notranslate">array</code></a> module provide additional examples of mutable sequence types. </div> There are currently two intrinsic mutable sequence types: <dl> <dt>Lists</dt><dd>The items of a list are arbitrary Python objects. Lists are formed by placing a comma-separated list of expressions in square brackets. (Note that there are no special cases needed to form lists of length 0 or 1.) </dd> <dt>Byte Arrays</dt><dd>A bytearray object is a mutable array. They are created by the built-in <a class="reference internal" href="../library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-func docutils literal notranslate">bytearray()</code></a> constructor. Aside from being mutable (and hence unhashable), byte arrays otherwise provide the same interface and functionality as immutable <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> objects. </dd> </dl> </section> </section> <section id="set-types"> <h3>3.2.6. Set types<a class="headerlink" href="#set-types" title="Link to this heading">¶</a></h3> These represent unordered, finite sets of unique, immutable objects. As such, they cannot be indexed by any subscript. However, they can be iterated over, and the built-in function <a class="reference internal" href="../library/functions.html#len" title="len"><code class="xref py py-func docutils literal notranslate">len()</code></a> returns the number of items in a set. Common uses for sets are fast membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference. For set elements, the same immutability rules apply as for dictionary keys. Note that numeric types obey the normal rules for numeric comparison: if two numbers compare equal (e.g., <code class="docutils literal notranslate">1</code> and <code class="docutils literal notranslate">1.0</code>), only one of them can be contained in a set. There are currently two intrinsic set types: <dl> <dt>Sets</dt><dd>These represent a mutable set. They are created by the built-in <a class="reference internal" href="../library/stdtypes.html#set" title="set"><code class="xref py py-func docutils literal notranslate">set()</code></a> constructor and can be modified afterwards by several methods, such as <code class="xref py py-meth docutils literal notranslate">add()</code>. </dd> <dt>Frozen sets</dt><dd>These represent an immutable set. They are created by the built-in <a class="reference internal" href="../library/stdtypes.html#frozenset" title="frozenset"><code class="xref py py-func docutils literal notranslate">frozenset()</code></a> constructor. As a frozenset is immutable and <a class="reference internal" href="../glossary.html#term-hashable">hashable</a>, it can be used again as an element of another set, or as a dictionary key. </dd> </dl> </section> <section id="mappings"> <h3>3.2.7. Mappings<a class="headerlink" href="#mappings" title="Link to this heading">¶</a></h3> These represent finite sets of objects indexed by arbitrary index sets. The subscript notation <code class="docutils literal notranslate">a[k]</code> selects the item indexed by <code class="docutils literal notranslate">k</code> from the mapping <code class="docutils literal notranslate">a</code>; this can be used in expressions and as the target of assignments or <a class="reference internal" href="simple_stmts.html#del"><code class="xref std std-keyword docutils literal notranslate">del</code></a> statements. The built-in function <a class="reference internal" href="../library/functions.html#len" title="len"><code class="xref py py-func docutils literal notranslate">len()</code></a> returns the number of items in a mapping. There is currently a single intrinsic mapping type: <section id="dictionaries"> <h4>3.2.7.1. Dictionaries<a class="headerlink" href="#dictionaries" title="Link to this heading">¶</a></h4> These represent finite sets of objects indexed by nearly arbitrary values. The only types of values not acceptable as keys are values containing lists or dictionaries or other mutable types that are compared by value rather than by object identity, the reason being that the efficient implementation of dictionaries requires a key’s hash value to remain constant. Numeric types used for keys obey the normal rules for numeric comparison: if two numbers compare equal (e.g., <code class="docutils literal notranslate">1</code> and <code class="docutils literal notranslate">1.0</code>) then they can be used interchangeably to index the same dictionary entry. Dictionaries preserve insertion order, meaning that keys will be produced in the same order they were added sequentially over the dictionary. Replacing an existing key does not change the order, however removing a key and re-inserting it will add it to the end instead of keeping its old place. Dictionaries are mutable; they can be created by the <code class="docutils literal notranslate">{}</code> notation (see section <a class="reference internal" href="expressions.html#dict">Dictionary displays</a>). The extension modules <a class="reference internal" href="../library/dbm.html#module-dbm.ndbm" title="dbm.ndbm: The New Database Manager (Unix)"><code class="xref py py-mod docutils literal notranslate">dbm.ndbm</code></a> and <a class="reference internal" href="../library/dbm.html#module-dbm.gnu" title="dbm.gnu: GNU database manager (Unix)"><code class="xref py py-mod docutils literal notranslate">dbm.gnu</code></a> provide additional examples of mapping types, as does the <a class="reference internal" href="../library/collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate">collections</code></a> module. <div class="versionchanged"> Changed in version 3.7: Dictionaries did not preserve insertion order in versions of Python before 3.6. In CPython 3.6, insertion order was preserved, but it was considered an implementation detail at that time rather than a language guarantee. </div> </section> </section> <section id="callable-types"> <h3>3.2.8. Callable types<a class="headerlink" href="#callable-types" title="Link to this heading">¶</a></h3> These are the types to which the function call operation (see section <a class="reference internal" href="expressions.html#calls">Calls</a>) can be applied: <section id="user-defined-functions"> <h4>3.2.8.1. User-defined functions<a class="headerlink" href="#user-defined-functions" title="Link to this heading">¶</a></h4> A user-defined function object is created by a function definition (see section <a class="reference internal" href="compound_stmts.html#function">Function definitions</a>). It should be called with an argument list containing the same number of items as the function’s formal parameter list. <section id="special-read-only-attributes"> <h5>3.2.8.1.1. Special read-only attributes<a class="headerlink" href="#special-read-only-attributes" title="Link to this heading">¶</a></h5> <table class="docutils align-default" id="index-35"> <thead> <tr class="row-odd"><th class="head">Attribute</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__globals__"> function.__globals__<a class="headerlink" href="#function.__globals__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A reference to the <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dictionary</code></a> that holds the function’s <a class="reference internal" href="executionmodel.html#naming">global variables</a> – the global namespace of the module in which the function was defined.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__closure__"> function.__closure__<a class="headerlink" href="#function.__closure__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td><code class="docutils literal notranslate">None</code> or a <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> of cells that contain bindings for the names specified in the <a class="reference internal" href="#codeobject.co_freevars" title="codeobject.co_freevars"><code class="xref py py-attr docutils literal notranslate">co_freevars</code></a> attribute of the function’s <a class="reference internal" href="#function.__code__" title="function.__code__"><code class="xref py py-attr docutils literal notranslate">code object</code></a>. A cell object has the attribute <code class="docutils literal notranslate">cell_contents</code>. This can be used to get the value of the cell, as well as set the value. </td> </tr> </tbody> </table> </section> <section id="special-writable-attributes"> <h5>3.2.8.1.2. Special writable attributes<a class="headerlink" href="#special-writable-attributes" title="Link to this heading">¶</a></h5> Most of these attributes check the type of the assigned value: <table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Attribute</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__doc__"> function.__doc__<a class="headerlink" href="#function.__doc__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The function’s documentation string, or <code class="docutils literal notranslate">None</code> if unavailable.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__name__"> function.__name__<a class="headerlink" href="#function.__name__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The function’s name. See also: <a class="reference internal" href="../library/stdtypes.html#definition.__name__" title="definition.__name__"><code class="xref py py-attr docutils literal notranslate">__name__ attributes</code></a>.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__qualname__"> function.__qualname__<a class="headerlink" href="#function.__qualname__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The function’s <a class="reference internal" href="../glossary.html#term-qualified-name">qualified name</a>. See also: <a class="reference internal" href="../library/stdtypes.html#definition.__qualname__" title="definition.__qualname__"><code class="xref py py-attr docutils literal notranslate">__qualname__ attributes</code></a>. <div class="versionadded"> Added in version 3.3. </div> </td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__module__"> function.__module__<a class="headerlink" href="#function.__module__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The name of the module the function was defined in, or <code class="docutils literal notranslate">None</code> if unavailable.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__defaults__"> function.__defaults__<a class="headerlink" href="#function.__defaults__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing default <a class="reference internal" href="../glossary.html#term-parameter">parameter</a> values for those parameters that have defaults, or <code class="docutils literal notranslate">None</code> if no parameters have a default value.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__code__"> function.__code__<a class="headerlink" href="#function.__code__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The <a class="reference internal" href="#code-objects">code object</a> representing the compiled function body.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__dict__"> function.__dict__<a class="headerlink" href="#function.__dict__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The namespace supporting arbitrary function attributes. See also: <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__ attributes</code></a>.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__annotations__"> function.__annotations__<a class="headerlink" href="#function.__annotations__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dictionary</code></a> containing annotations of <a class="reference internal" href="../glossary.html#term-parameter">parameters</a>. The keys of the dictionary are the parameter names, and <code class="docutils literal notranslate">'return'</code> for the return annotation, if provided. See also: <a class="reference internal" href="../howto/annotations.html#annotations-howto">Annotations Best Practices</a>.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__kwdefaults__"> function.__kwdefaults__<a class="headerlink" href="#function.__kwdefaults__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dictionary</code></a> containing defaults for keyword-only <a class="reference internal" href="../glossary.html#term-parameter">parameters</a>.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="function.__type_params__"> function.__type_params__<a class="headerlink" href="#function.__type_params__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the <a class="reference internal" href="compound_stmts.html#type-params">type parameters</a> of a <a class="reference internal" href="compound_stmts.html#generic-functions">generic function</a>. <div class="versionadded"> Added in version 3.12. </div> </td> </tr> </tbody> </table> Function objects also support getting and setting arbitrary attributes, which can be used, for example, to attach metadata to functions. Regular attribute dot-notation is used to get and set such attributes. <div class="impl-detail compound"> CPython implementation detail: CPython’s current implementation only supports function attributes on user-defined functions. Function attributes on <a class="reference internal" href="#builtin-functions">built-in functions</a> may be supported in the future. </div> Additional information about a function’s definition can be retrieved from its <a class="reference internal" href="#code-objects">code object</a> (accessible via the <a class="reference internal" href="#function.__code__" title="function.__code__"><code class="xref py py-attr docutils literal notranslate">__code__</code></a> attribute). </section> </section> <section id="instance-methods"> <h4>3.2.8.2. Instance methods<a class="headerlink" href="#instance-methods" title="Link to this heading">¶</a></h4> An instance method object combines a class, a class instance and any callable object (normally a user-defined function). Special read-only attributes: <table class="docutils align-default"> <tbody> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="method.__self__"> method.__self__<a class="headerlink" href="#method.__self__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Refers to the class instance object to which the method is <a class="reference internal" href="#method-binding">bound</a></td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="method.__func__"> method.__func__<a class="headerlink" href="#method.__func__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Refers to the original <a class="reference internal" href="#user-defined-funcs">function object</a></td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="method.__doc__"> method.__doc__<a class="headerlink" href="#method.__doc__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The method’s documentation (same as <a class="reference internal" href="#function.__doc__" title="function.__doc__"><code class="xref py py-attr docutils literal notranslate">method.__func__.__doc__</code></a>). A <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">string</code></a> if the original function had a docstring, else <code class="docutils literal notranslate">None</code>.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="method.__name__"> method.__name__<a class="headerlink" href="#method.__name__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The name of the method (same as <a class="reference internal" href="#function.__name__" title="function.__name__"><code class="xref py py-attr docutils literal notranslate">method.__func__.__name__</code></a>)</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="method.__module__"> method.__module__<a class="headerlink" href="#method.__module__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The name of the module the method was defined in, or <code class="docutils literal notranslate">None</code> if unavailable.</td> </tr> </tbody> </table> Methods also support accessing (but not setting) the arbitrary function attributes on the underlying <a class="reference internal" href="#user-defined-funcs">function object</a>. User-defined method objects may be created when getting an attribute of a class (perhaps via an instance of that class), if that attribute is a user-defined <a class="reference internal" href="#user-defined-funcs">function object</a> or a <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-class docutils literal notranslate">classmethod</code></a> object. When an instance method object is created by retrieving a user-defined <a class="reference internal" href="#user-defined-funcs">function object</a> from a class via one of its instances, its <a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">__self__</code></a> attribute is the instance, and the method object is said to be bound. The new method’s <a class="reference internal" href="#method.__func__" title="method.__func__"><code class="xref py py-attr docutils literal notranslate">__func__</code></a> attribute is the original function object. When an instance method object is created by retrieving a <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-class docutils literal notranslate">classmethod</code></a> object from a class or instance, its <a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">__self__</code></a> attribute is the class itself, and its <a class="reference internal" href="#method.__func__" title="method.__func__"><code class="xref py py-attr docutils literal notranslate">__func__</code></a> attribute is the function object underlying the class method. When an instance method object is called, the underlying function (<a class="reference internal" href="#method.__func__" title="method.__func__"><code class="xref py py-attr docutils literal notranslate">__func__</code></a>) is called, inserting the class instance (<a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">__self__</code></a>) in front of the argument list. For instance, when <code class="xref py py-class docutils literal notranslate">C</code> is a class which contains a definition for a function <code class="xref py py-meth docutils literal notranslate">f()</code>, and <code class="docutils literal notranslate">x</code> is an instance of <code class="xref py py-class docutils literal notranslate">C</code>, calling <code class="docutils literal notranslate">x.f(1)</code> is equivalent to calling <code class="docutils literal notranslate">C.f(x, 1)</code>. When an instance method object is derived from a <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-class docutils literal notranslate">classmethod</code></a> object, the “class instance” stored in <a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">__self__</code></a> will actually be the class itself, so that calling either <code class="docutils literal notranslate">x.f(1)</code> or <code class="docutils literal notranslate">C.f(1)</code> is equivalent to calling <code class="docutils literal notranslate">f(C,1)</code> where <code class="docutils literal notranslate">f</code> is the underlying function. It is important to note that user-defined functions which are attributes of a class instance are not converted to bound methods; this only happens when the function is an attribute of the class. </section> <section id="generator-functions"> <h4>3.2.8.3. Generator functions<a class="headerlink" href="#generator-functions" title="Link to this heading">¶</a></h4> A function or method which uses the <a class="reference internal" href="simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> statement (see section <a class="reference internal" href="simple_stmts.html#yield">The yield statement</a>) is called a generator function. Such a function, when called, always returns an <a class="reference internal" href="../glossary.html#term-iterator">iterator</a> object which can be used to execute the body of the function: calling the iterator’s <a class="reference internal" href="../library/stdtypes.html#iterator.__next__" title="iterator.__next__"><code class="xref py py-meth docutils literal notranslate">iterator.__next__()</code></a> method will cause the function to execute until it provides a value using the <code class="xref std std-keyword docutils literal notranslate">yield</code> statement. When the function executes a <a class="reference internal" href="simple_stmts.html#return"><code class="xref std std-keyword docutils literal notranslate">return</code></a> statement or falls off the end, a <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a> exception is raised and the iterator will have reached the end of the set of values to be returned. </section> <section id="coroutine-functions"> <h4>3.2.8.4. Coroutine functions<a class="headerlink" href="#coroutine-functions" title="Link to this heading">¶</a></h4> A function or method which is defined using <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate">async def</code></a> is called a coroutine function. Such a function, when called, returns a <a class="reference internal" href="../glossary.html#term-coroutine">coroutine</a> object. It may contain <a class="reference internal" href="expressions.html#await"><code class="xref std std-keyword docutils literal notranslate">await</code></a> expressions, as well as <a class="reference internal" href="compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate">async with</code></a> and <a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a> statements. See also the <a class="reference internal" href="#coroutine-objects">Coroutine Objects</a> section. </section> <section id="asynchronous-generator-functions"> <h4>3.2.8.5. Asynchronous generator functions<a class="headerlink" href="#asynchronous-generator-functions" title="Link to this heading">¶</a></h4> A function or method which is defined using <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate">async def</code></a> and which uses the <a class="reference internal" href="simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> statement is called a asynchronous generator function. Such a function, when called, returns an <a class="reference internal" href="../glossary.html#term-asynchronous-iterator">asynchronous iterator</a> object which can be used in an <a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a> statement to execute the body of the function. Calling the asynchronous iterator’s <a class="reference internal" href="#object.__anext__" title="object.__anext__"><code class="xref py py-meth docutils literal notranslate">aiterator.__anext__</code></a> method will return an <a class="reference internal" href="../glossary.html#term-awaitable">awaitable</a> which when awaited will execute until it provides a value using the <a class="reference internal" href="simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> expression. When the function executes an empty <a class="reference internal" href="simple_stmts.html#return"><code class="xref std std-keyword docutils literal notranslate">return</code></a> statement or falls off the end, a <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate">StopAsyncIteration</code></a> exception is raised and the asynchronous iterator will have reached the end of the set of values to be yielded. </section> <section id="built-in-functions"> <h4>3.2.8.6. Built-in functions<a class="headerlink" href="#built-in-functions" title="Link to this heading">¶</a></h4> A built-in function object is a wrapper around a C function. Examples of built-in functions are <a class="reference internal" href="../library/functions.html#len" title="len"><code class="xref py py-func docutils literal notranslate">len()</code></a> and <a class="reference internal" href="../library/math.html#math.sin" title="math.sin"><code class="xref py py-func docutils literal notranslate">math.sin()</code></a> (<a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate">math</code></a> is a standard built-in module). The number and type of the arguments are determined by the C function. Special read-only attributes: <ul class="simple"> <li><code class="xref py py-attr docutils literal notranslate">__doc__</code> is the function’s documentation string, or <code class="docutils literal notranslate">None</code> if unavailable. See <a class="reference internal" href="#function.__doc__" title="function.__doc__"><code class="xref py py-attr docutils literal notranslate">function.__doc__</code></a>.</li> <li><code class="xref py py-attr docutils literal notranslate">__name__</code> is the function’s name. See <a class="reference internal" href="#function.__name__" title="function.__name__"><code class="xref py py-attr docutils literal notranslate">function.__name__</code></a>.</li> <li><code class="xref py py-attr docutils literal notranslate">__self__</code> is set to <code class="docutils literal notranslate">None</code> (but see the next item).</li> <li><code class="xref py py-attr docutils literal notranslate">__module__</code> is the name of the module the function was defined in or <code class="docutils literal notranslate">None</code> if unavailable. See <a class="reference internal" href="#function.__module__" title="function.__module__"><code class="xref py py-attr docutils literal notranslate">function.__module__</code></a>.</li> </ul> </section> <section id="built-in-methods"> <h4>3.2.8.7. Built-in methods<a class="headerlink" href="#built-in-methods" title="Link to this heading">¶</a></h4> This is really a different disguise of a built-in function, this time containing an object passed to the C function as an implicit extra argument. An example of a built-in method is <code class="docutils literal notranslate">alist.append()</code>, assuming alist is a list object. In this case, the special read-only attribute <code class="xref py py-attr docutils literal notranslate">__self__</code> is set to the object denoted by alist. (The attribute has the same semantics as it does with <a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">other instance methods</code></a>.) </section> <section id="classes"> <h4>3.2.8.8. Classes<a class="headerlink" href="#classes" title="Link to this heading">¶</a></h4> Classes are callable. These objects normally act as factories for new instances of themselves, but variations are possible for class types that override <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a>. The arguments of the call are passed to <code class="xref py py-meth docutils literal notranslate">__new__()</code> and, in the typical case, to <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> to initialize the new instance. </section> <section id="class-instances"> <h4>3.2.8.9. Class Instances<a class="headerlink" href="#class-instances" title="Link to this heading">¶</a></h4> Instances of arbitrary classes can be made callable by defining a <a class="reference internal" href="#object.__call__" title="object.__call__"><code class="xref py py-meth docutils literal notranslate">__call__()</code></a> method in their class. </section> </section> <section id="modules"> <h3>3.2.9. Modules<a class="headerlink" href="#modules" title="Link to this heading">¶</a></h3> Modules are a basic organizational unit of Python code, and are created by the <a class="reference internal" href="import.html#importsystem">import system</a> as invoked either by the <a class="reference internal" href="simple_stmts.html#import"><code class="xref std std-keyword docutils literal notranslate">import</code></a> statement, or by calling functions such as <a class="reference internal" href="../library/importlib.html#importlib.import_module" title="importlib.import_module"><code class="xref py py-func docutils literal notranslate">importlib.import_module()</code></a> and built-in <a class="reference internal" href="../library/functions.html#import__" title="__import__"><code class="xref py py-func docutils literal notranslate">__import__()</code></a>. A module object has a namespace implemented by a <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dictionary</code></a> object (this is the dictionary referenced by the <a class="reference internal" href="#function.__globals__" title="function.__globals__"><code class="xref py py-attr docutils literal notranslate">__globals__</code></a> attribute of functions defined in the module). Attribute references are translated to lookups in this dictionary, e.g., <code class="docutils literal notranslate">m.x</code> is equivalent to <code class="docutils literal notranslate">m.__dict__["x"]</code>. A module object does not contain the code object used to initialize the module (since it isn’t needed once the initialization is done). Attribute assignment updates the module’s namespace dictionary, e.g., <code class="docutils literal notranslate">m.x = 1</code> is equivalent to <code class="docutils literal notranslate">m.__dict__["x"] = 1</code>. <section id="import-related-attributes-on-module-objects"> <h4>3.2.9.1. Import-related attributes on module objects<a class="headerlink" href="#import-related-attributes-on-module-objects" title="Link to this heading">¶</a></h4> Module objects have the following attributes that relate to the <a class="reference internal" href="import.html#importsystem">import system</a>. When a module is created using the machinery associated with the import system, these attributes are filled in based on the module’s <a class="reference internal" href="../glossary.html#term-module-spec">spec</a>, before the <a class="reference internal" href="../glossary.html#term-loader">loader</a> executes and loads the module. To create a module dynamically rather than using the import system, it’s recommended to use <a class="reference internal" href="../library/importlib.html#importlib.util.module_from_spec" title="importlib.util.module_from_spec"><code class="xref py py-func docutils literal notranslate">importlib.util.module_from_spec()</code></a>, which will set the various import-controlled attributes to appropriate values. It’s also possible to use the <a class="reference internal" href="../library/types.html#types.ModuleType" title="types.ModuleType"><code class="xref py py-class docutils literal notranslate">types.ModuleType</code></a> constructor to create modules directly, but this technique is more error-prone, as most attributes must be manually set on the module object after it has been created when using this approach. <div class="admonition caution"> Caution With the exception of <a class="reference internal" href="#module.__name__" title="module.__name__"><code class="xref py py-attr docutils literal notranslate">__name__</code></a>, it is strongly recommended that you rely on <a class="reference internal" href="#module.__spec__" title="module.__spec__"><code class="xref py py-attr docutils literal notranslate">__spec__</code></a> and its attributes instead of any of the other individual attributes listed in this subsection. Note that updating an attribute on <code class="xref py py-attr docutils literal notranslate">__spec__</code> will not update the corresponding attribute on the module itself: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> import typing >>> typing.__name__, typing.__spec__.name ('typing', 'typing') >>> typing.__spec__.name = 'spelling' >>> typing.__name__, typing.__spec__.name ('typing', 'spelling') >>> typing.__name__ = 'keyboard_smashing' >>> typing.__name__, typing.__spec__.name ('keyboard_smashing', 'spelling') </pre></div> </div> </div> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__name__"> module.__name__<a class="headerlink" href="#module.__name__" title="Link to this definition">¶</a></dt> <dd>The name used to uniquely identify the module in the import system. For a directly executed module, this will be set to <code class="docutils literal notranslate">"__main__"</code>. This attribute must be set to the fully qualified name of the module. It is expected to match the value of <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.name" title="importlib.machinery.ModuleSpec.name"><code class="xref py py-attr docutils literal notranslate">module.__spec__.name</code></a>. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__spec__"> module.__spec__<a class="headerlink" href="#module.__spec__" title="Link to this definition">¶</a></dt> <dd>A record of the module’s import-system-related state. Set to the <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec" title="importlib.machinery.ModuleSpec"><code class="xref py py-class docutils literal notranslate">module spec</code></a> that was used when importing the module. See <a class="reference internal" href="import.html#module-specs">Module specs</a> for more details. <div class="versionadded"> Added in version 3.4. </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__package__"> module.__package__<a class="headerlink" href="#module.__package__" title="Link to this definition">¶</a></dt> <dd>The <a class="reference internal" href="../glossary.html#term-package">package</a> a module belongs to. If the module is top-level (that is, not a part of any specific package) then the attribute should be set to <code class="docutils literal notranslate">''</code> (the empty string). Otherwise, it should be set to the name of the module’s package (which can be equal to <a class="reference internal" href="#module.__name__" title="module.__name__"><code class="xref py py-attr docutils literal notranslate">module.__name__</code></a> if the module itself is a package). See <a class="pep reference external" href="https://peps.python.org/pep-0366/">PEP 366</a> for further details. This attribute is used instead of <a class="reference internal" href="#module.__name__" title="module.__name__"><code class="xref py py-attr docutils literal notranslate">__name__</code></a> to calculate explicit relative imports for main modules. It defaults to <code class="docutils literal notranslate">None</code> for modules created dynamically using the <a class="reference internal" href="../library/types.html#types.ModuleType" title="types.ModuleType"><code class="xref py py-class docutils literal notranslate">types.ModuleType</code></a> constructor; use <a class="reference internal" href="../library/importlib.html#importlib.util.module_from_spec" title="importlib.util.module_from_spec"><code class="xref py py-func docutils literal notranslate">importlib.util.module_from_spec()</code></a> instead to ensure the attribute is set to a <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>. It is strongly recommended that you use <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.parent" title="importlib.machinery.ModuleSpec.parent"><code class="xref py py-attr docutils literal notranslate">module.__spec__.parent</code></a> instead of <code class="xref py py-attr docutils literal notranslate">module.__package__</code>. <a class="reference internal" href="#module.__package__" title="module.__package__"><code class="xref py py-attr docutils literal notranslate">__package__</code></a> is now only used as a fallback if <code class="xref py py-attr docutils literal notranslate">__spec__.parent</code> is not set, and this fallback path is deprecated. <div class="versionchanged"> Changed in version 3.4: This attribute now defaults to <code class="docutils literal notranslate">None</code> for modules created dynamically using the <a class="reference internal" href="../library/types.html#types.ModuleType" title="types.ModuleType"><code class="xref py py-class docutils literal notranslate">types.ModuleType</code></a> constructor. Previously the attribute was optional. </div> <div class="versionchanged"> Changed in version 3.6: The value of <code class="xref py py-attr docutils literal notranslate">__package__</code> is expected to be the same as <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.parent" title="importlib.machinery.ModuleSpec.parent"><code class="xref py py-attr docutils literal notranslate">__spec__.parent</code></a>. <a class="reference internal" href="#module.__package__" title="module.__package__"><code class="xref py py-attr docutils literal notranslate">__package__</code></a> is now only used as a fallback during import resolution if <code class="xref py py-attr docutils literal notranslate">__spec__.parent</code> is not defined. </div> <div class="versionchanged"> Changed in version 3.10: <a class="reference internal" href="../library/exceptions.html#ImportWarning" title="ImportWarning"><code class="xref py py-exc docutils literal notranslate">ImportWarning</code></a> is raised if an import resolution falls back to <code class="xref py py-attr docutils literal notranslate">__package__</code> instead of <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.parent" title="importlib.machinery.ModuleSpec.parent"><code class="xref py py-attr docutils literal notranslate">__spec__.parent</code></a>. </div> <div class="versionchanged"> Changed in version 3.12: Raise <a class="reference internal" href="../library/exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> instead of <a class="reference internal" href="../library/exceptions.html#ImportWarning" title="ImportWarning"><code class="xref py py-exc docutils literal notranslate">ImportWarning</code></a> when falling back to <code class="xref py py-attr docutils literal notranslate">__package__</code> during import resolution. </div> <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.15: <code class="xref py py-attr docutils literal notranslate">__package__</code> will cease to be set or taken into consideration by the import system or standard library. </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__loader__"> module.__loader__<a class="headerlink" href="#module.__loader__" title="Link to this definition">¶</a></dt> <dd>The <a class="reference internal" href="../glossary.html#term-loader">loader</a> object that the import machinery used to load the module. This attribute is mostly useful for introspection, but can be used for additional loader-specific functionality, for example getting data associated with a loader. <code class="xref py py-attr docutils literal notranslate">__loader__</code> defaults to <code class="docutils literal notranslate">None</code> for modules created dynamically using the <a class="reference internal" href="../library/types.html#types.ModuleType" title="types.ModuleType"><code class="xref py py-class docutils literal notranslate">types.ModuleType</code></a> constructor; use <a class="reference internal" href="../library/importlib.html#importlib.util.module_from_spec" title="importlib.util.module_from_spec"><code class="xref py py-func docutils literal notranslate">importlib.util.module_from_spec()</code></a> instead to ensure the attribute is set to a <a class="reference internal" href="../glossary.html#term-loader">loader</a> object. It is strongly recommended that you use <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.loader" title="importlib.machinery.ModuleSpec.loader"><code class="xref py py-attr docutils literal notranslate">module.__spec__.loader</code></a> instead of <code class="xref py py-attr docutils literal notranslate">module.__loader__</code>. <div class="versionchanged"> Changed in version 3.4: This attribute now defaults to <code class="docutils literal notranslate">None</code> for modules created dynamically using the <a class="reference internal" href="../library/types.html#types.ModuleType" title="types.ModuleType"><code class="xref py py-class docutils literal notranslate">types.ModuleType</code></a> constructor. Previously the attribute was optional. </div> <div class="deprecated-removed"> Deprecated since version 3.12, will be removed in version 3.16: Setting <code class="xref py py-attr docutils literal notranslate">__loader__</code> on a module while failing to set <code class="xref py py-attr docutils literal notranslate">__spec__.loader</code> is deprecated. In Python 3.16, <code class="xref py py-attr docutils literal notranslate">__loader__</code> will cease to be set or taken into consideration by the import system or the standard library. </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__path__"> module.__path__<a class="headerlink" href="#module.__path__" title="Link to this definition">¶</a></dt> <dd>A (possibly empty) <a class="reference internal" href="../glossary.html#term-sequence">sequence</a> of strings enumerating the locations where the package’s submodules will be found. Non-package modules should not have a <code class="xref py py-attr docutils literal notranslate">__path__</code> attribute. See <a class="reference internal" href="import.html#package-path-rules">__path__ attributes on modules</a> for more details. It is strongly recommended that you use <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.submodule_search_locations" title="importlib.machinery.ModuleSpec.submodule_search_locations"><code class="xref py py-attr docutils literal notranslate">module.__spec__.submodule_search_locations</code></a> instead of <code class="xref py py-attr docutils literal notranslate">module.__path__</code>. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__file__"> module.__file__<a class="headerlink" href="#module.__file__" title="Link to this definition">¶</a></dt> <dd></dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__cached__"> module.__cached__<a class="headerlink" href="#module.__cached__" title="Link to this definition">¶</a></dt> <dd><code class="xref py py-attr docutils literal notranslate">__file__</code> and <code class="xref py py-attr docutils literal notranslate">__cached__</code> are both optional attributes that may or may not be set. Both attributes should be a <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> when they are available. <code class="xref py py-attr docutils literal notranslate">__file__</code> indicates the pathname of the file from which the module was loaded (if loaded from a file), or the pathname of the shared library file for extension modules loaded dynamically from a shared library. It might be missing for certain types of modules, such as C modules that are statically linked into the interpreter, and the <a class="reference internal" href="import.html#importsystem">import system</a> may opt to leave it unset if it has no semantic meaning (for example, a module loaded from a database). If <code class="xref py py-attr docutils literal notranslate">__file__</code> is set then the <code class="xref py py-attr docutils literal notranslate">__cached__</code> attribute might also be set, which is the path to any compiled version of the code (for example, a byte-compiled file). The file does not need to exist to set this attribute; the path can simply point to where the compiled file would exist (see <a class="pep reference external" href="https://peps.python.org/pep-3147/">PEP 3147</a>). Note that <code class="xref py py-attr docutils literal notranslate">__cached__</code> may be set even if <code class="xref py py-attr docutils literal notranslate">__file__</code> is not set. However, that scenario is quite atypical. Ultimately, the <a class="reference internal" href="../glossary.html#term-loader">loader</a> is what makes use of the module spec provided by the <a class="reference internal" href="../glossary.html#term-finder">finder</a> (from which <code class="xref py py-attr docutils literal notranslate">__file__</code> and <code class="xref py py-attr docutils literal notranslate">__cached__</code> are derived). So if a loader can load from a cached module but otherwise does not load from a file, that atypical scenario may be appropriate. It is strongly recommended that you use <a class="reference internal" href="../library/importlib.html#importlib.machinery.ModuleSpec.cached" title="importlib.machinery.ModuleSpec.cached"><code class="xref py py-attr docutils literal notranslate">module.__spec__.cached</code></a> instead of <code class="xref py py-attr docutils literal notranslate">module.__cached__</code>. <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.15: Setting <code class="xref py py-attr docutils literal notranslate">__cached__</code> on a module while failing to set <code class="xref py py-attr docutils literal notranslate">__spec__.cached</code> is deprecated. In Python 3.15, <code class="xref py py-attr docutils literal notranslate">__cached__</code> will cease to be set or taken into consideration by the import system or standard library. </div> </dd></dl> </section> <section id="other-writable-attributes-on-module-objects"> <h4>3.2.9.2. Other writable attributes on module objects<a class="headerlink" href="#other-writable-attributes-on-module-objects" title="Link to this heading">¶</a></h4> As well as the import-related attributes listed above, module objects also have the following writable attributes: <dl class="py attribute"> <dt class="sig sig-object py" id="module.__doc__"> module.__doc__<a class="headerlink" href="#module.__doc__" title="Link to this definition">¶</a></dt> <dd>The module’s documentation string, or <code class="docutils literal notranslate">None</code> if unavailable. See also: <a class="reference internal" href="../library/stdtypes.html#definition.__doc__" title="definition.__doc__"><code class="xref py py-attr docutils literal notranslate">__doc__ attributes</code></a>. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="module.__annotations__"> module.__annotations__<a class="headerlink" href="#module.__annotations__" title="Link to this definition">¶</a></dt> <dd>A dictionary containing <a class="reference internal" href="../glossary.html#term-variable-annotation">variable annotations</a> collected during module body execution. For best practices on working with <a class="reference internal" href="#module.__annotations__" title="module.__annotations__"><code class="xref py py-attr docutils literal notranslate">__annotations__</code></a>, please see <a class="reference internal" href="../howto/annotations.html#annotations-howto">Annotations Best Practices</a>. </dd></dl> </section> <section id="module-dictionaries"> <h4>3.2.9.3. Module dictionaries<a class="headerlink" href="#module-dictionaries" title="Link to this heading">¶</a></h4> Module objects also have the following special read-only attribute: <dl class="py attribute" id="index-48"> <dt class="sig sig-object py" id="module.__dict__"> module.__dict__<a class="headerlink" href="#module.__dict__" title="Link to this definition">¶</a></dt> <dd>The module’s namespace as a dictionary object. Uniquely among the attributes listed here, <code class="xref py py-attr docutils literal notranslate">__dict__</code> cannot be accessed as a global variable from within a module; it can only be accessed as an attribute on module objects. <div class="impl-detail compound"> CPython implementation detail: Because of the way CPython clears module dictionaries, the module dictionary will be cleared when the module falls out of scope even if the dictionary still has live references. To avoid this, copy the dictionary or keep the module around while using its dictionary directly. </div> </dd></dl> </section> </section> <section id="custom-classes"> <h3>3.2.10. Custom classes<a class="headerlink" href="#custom-classes" title="Link to this heading">¶</a></h3> Custom class types are typically created by class definitions (see section <a class="reference internal" href="compound_stmts.html#class">Class definitions</a>). A class has a namespace implemented by a dictionary object. Class attribute references are translated to lookups in this dictionary, e.g., <code class="docutils literal notranslate">C.x</code> is translated to <code class="docutils literal notranslate">C.__dict__["x"]</code> (although there are a number of hooks which allow for other means of locating attributes). When the attribute name is not found there, the attribute search continues in the base classes. This search of the base classes uses the C3 method resolution order which behaves correctly even in the presence of ‘diamond’ inheritance structures where there are multiple inheritance paths leading back to a common ancestor. Additional details on the C3 MRO used by Python can be found at <a class="reference internal" href="../howto/mro.html#python-2-3-mro">The Python 2.3 Method Resolution Order</a>. When a class attribute reference (for class <code class="xref py py-class docutils literal notranslate">C</code>, say) would yield a class method object, it is transformed into an instance method object whose <a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">__self__</code></a> attribute is <code class="xref py py-class docutils literal notranslate">C</code>. When it would yield a <a class="reference internal" href="../library/functions.html#staticmethod" title="staticmethod"><code class="xref py py-class docutils literal notranslate">staticmethod</code></a> object, it is transformed into the object wrapped by the static method object. See section <a class="reference internal" href="#descriptors">Implementing Descriptors</a> for another way in which attributes retrieved from a class may differ from those actually contained in its <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a>. Class attribute assignments update the class’s dictionary, never the dictionary of a base class. A class object can be called (see above) to yield a class instance (see below). <section id="special-attributes"> <h4>3.2.10.1. Special attributes<a class="headerlink" href="#special-attributes" title="Link to this heading">¶</a></h4> <table class="docutils align-default" id="index-52"> <thead> <tr class="row-odd"><th class="head">Attribute</th> <th class="head">Meaning</th> </tr> </thead> <tbody> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__name__"> type.__name__<a class="headerlink" href="#type.__name__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The class’s name. See also: <a class="reference internal" href="../library/stdtypes.html#definition.__name__" title="definition.__name__"><code class="xref py py-attr docutils literal notranslate">__name__ attributes</code></a>.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__qualname__"> type.__qualname__<a class="headerlink" href="#type.__qualname__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The class’s <a class="reference internal" href="../glossary.html#term-qualified-name">qualified name</a>. See also: <a class="reference internal" href="../library/stdtypes.html#definition.__qualname__" title="definition.__qualname__"><code class="xref py py-attr docutils literal notranslate">__qualname__ attributes</code></a>.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__module__"> type.__module__<a class="headerlink" href="#type.__module__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The name of the module in which the class was defined.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__dict__"> type.__dict__<a class="headerlink" href="#type.__dict__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/types.html#types.MappingProxyType" title="types.MappingProxyType"><code class="xref py py-class docutils literal notranslate">mapping proxy</code></a> providing a read-only view of the class’s namespace. See also: <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__ attributes</code></a>.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__bases__"> type.__bases__<a class="headerlink" href="#type.__bases__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the class’s bases. In most cases, for a class defined as <code class="docutils literal notranslate">class X(A, B, C)</code>, <code class="docutils literal notranslate">X.__bases__</code> will be exactly equal to <code class="docutils literal notranslate">(A, B, C)</code>.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__doc__"> type.__doc__<a class="headerlink" href="#type.__doc__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The class’s documentation string, or <code class="docutils literal notranslate">None</code> if undefined. Not inherited by subclasses.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__annotations__"> type.__annotations__<a class="headerlink" href="#type.__annotations__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A dictionary containing <a class="reference internal" href="../glossary.html#term-variable-annotation">variable annotations</a> collected during class body execution. For best practices on working with <code class="xref py py-attr docutils literal notranslate">__annotations__</code>, please see <a class="reference internal" href="../howto/annotations.html#annotations-howto">Annotations Best Practices</a>. <div class="admonition caution"> Caution Accessing the <code class="xref py py-attr docutils literal notranslate">__annotations__</code> attribute of a class object directly may yield incorrect results in the presence of metaclasses. In addition, the attribute may not exist for some classes. Use <a class="reference internal" href="../library/inspect.html#inspect.get_annotations" title="inspect.get_annotations"><code class="xref py py-func docutils literal notranslate">inspect.get_annotations()</code></a> to retrieve class annotations safely. </div> </td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__type_params__"> type.__type_params__<a class="headerlink" href="#type.__type_params__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the <a class="reference internal" href="compound_stmts.html#type-params">type parameters</a> of a <a class="reference internal" href="compound_stmts.html#generic-classes">generic class</a>. <div class="versionadded"> Added in version 3.12. </div> </td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__static_attributes__"> type.__static_attributes__<a class="headerlink" href="#type.__static_attributes__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing names of attributes of this class which are assigned through <code class="docutils literal notranslate">self.X</code> from any function in its body. <div class="versionadded"> Added in version 3.13. </div> </td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__firstlineno__"> type.__firstlineno__<a class="headerlink" href="#type.__firstlineno__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The line number of the first line of the class definition, including decorators. Setting the <code class="xref py py-attr docutils literal notranslate">__module__</code> attribute removes the <code class="xref py py-attr docutils literal notranslate">__firstlineno__</code> item from the type’s dictionary. <div class="versionadded"> Added in version 3.13. </div> </td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="type.__mro__"> type.__mro__<a class="headerlink" href="#type.__mro__" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> of classes that are considered when looking for base classes during method resolution.</td> </tr> </tbody> </table> </section> <section id="special-methods"> <h4>3.2.10.2. Special methods<a class="headerlink" href="#special-methods" title="Link to this heading">¶</a></h4> In addition to the special attributes described above, all Python classes also have the following two methods available: <dl class="py method"> <dt class="sig sig-object py" id="type.mro"> type.mro()<a class="headerlink" href="#type.mro" title="Link to this definition">¶</a></dt> <dd>This method can be overridden by a metaclass to customize the method resolution order for its instances. It is called at class instantiation, and its result is stored in <a class="reference internal" href="#type.__mro__" title="type.__mro__"><code class="xref py py-attr docutils literal notranslate">__mro__</code></a>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="type.__subclasses__"> type.__subclasses__()<a class="headerlink" href="#type.__subclasses__" title="Link to this definition">¶</a></dt> <dd>Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. The list is in definition order. Example: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> class A: pass >>> class B(A): pass >>> A.__subclasses__() [<class 'B'>] </pre></div> </div> </dd></dl> </section> </section> <section id="id4"> <h3>3.2.11. Class instances<a class="headerlink" href="#id4" title="Link to this heading">¶</a></h3> A class instance is created by calling a class object (see above). A class instance has a namespace implemented as a dictionary which is the first place in which attribute references are searched. When an attribute is not found there, and the instance’s class has an attribute by that name, the search continues with the class attributes. If a class attribute is found that is a user-defined function object, it is transformed into an instance method object whose <a class="reference internal" href="#method.__self__" title="method.__self__"><code class="xref py py-attr docutils literal notranslate">__self__</code></a> attribute is the instance. Static method and class method objects are also transformed; see above under “Classes”. See section <a class="reference internal" href="#descriptors">Implementing Descriptors</a> for another way in which attributes of a class retrieved via its instances may differ from the objects actually stored in the class’s <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a>. If no class attribute is found, and the object’s class has a <a class="reference internal" href="#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate">__getattr__()</code></a> method, that is called to satisfy the lookup. Attribute assignments and deletions update the instance’s dictionary, never a class’s dictionary. If the class has a <a class="reference internal" href="#object.__setattr__" title="object.__setattr__"><code class="xref py py-meth docutils literal notranslate">__setattr__()</code></a> or <a class="reference internal" href="#object.__delattr__" title="object.__delattr__"><code class="xref py py-meth docutils literal notranslate">__delattr__()</code></a> method, this is called instead of updating the instance dictionary directly. Class instances can pretend to be numbers, sequences, or mappings if they have methods with certain special names. See section <a class="reference internal" href="#specialnames">Special method names</a>. <section id="id5"> <h4>3.2.11.1. Special attributes<a class="headerlink" href="#id5" title="Link to this heading">¶</a></h4> <dl class="py attribute" id="index-56"> <dt class="sig sig-object py" id="object.__class__"> object.__class__<a class="headerlink" href="#object.__class__" title="Link to this definition">¶</a></dt> <dd>The class to which a class instance belongs. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="object.__dict__"> object.__dict__<a class="headerlink" href="#object.__dict__" title="Link to this definition">¶</a></dt> <dd>A dictionary or other mapping object used to store an object’s (writable) attributes. Not all instances have a <code class="xref py py-attr docutils literal notranslate">__dict__</code> attribute; see the section on <a class="reference internal" href="#slots">__slots__</a> for more details. </dd></dl> </section> </section> <section id="i-o-objects-also-known-as-file-objects"> <h3>3.2.12. I/O objects (also known as file objects)<a class="headerlink" href="#i-o-objects-also-known-as-file-objects" title="Link to this heading">¶</a></h3> A <a class="reference internal" href="../glossary.html#term-file-object">file object</a> represents an open file. Various shortcuts are available to create file objects: the <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> built-in function, and also <a class="reference internal" href="../library/os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate">os.popen()</code></a>, <a class="reference internal" href="../library/os.html#os.fdopen" title="os.fdopen"><code class="xref py py-func docutils literal notranslate">os.fdopen()</code></a>, and the <a class="reference internal" href="../library/socket.html#socket.socket.makefile" title="socket.socket.makefile"><code class="xref py py-meth docutils literal notranslate">makefile()</code></a> method of socket objects (and perhaps by other functions or methods provided by extension modules). The objects <code class="docutils literal notranslate">sys.stdin</code>, <code class="docutils literal notranslate">sys.stdout</code> and <code class="docutils literal notranslate">sys.stderr</code> are initialized to file objects corresponding to the interpreter’s standard input, output and error streams; they are all open in text mode and therefore follow the interface defined by the <a class="reference internal" href="../library/io.html#io.TextIOBase" title="io.TextIOBase"><code class="xref py py-class docutils literal notranslate">io.TextIOBase</code></a> abstract class. </section> <section id="internal-types"> <h3>3.2.13. Internal types<a class="headerlink" href="#internal-types" title="Link to this heading">¶</a></h3> A few types used internally by the interpreter are exposed to the user. Their definitions may change with future versions of the interpreter, but they are mentioned here for completeness. <section id="code-objects"> <h4>3.2.13.1. Code objects<a class="headerlink" href="#code-objects" title="Link to this heading">¶</a></h4> Code objects represent byte-compiled executable Python code, or <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a>. The difference between a code object and a function object is that the function object contains an explicit reference to the function’s globals (the module in which it was defined), while a code object contains no context; also the default argument values are stored in the function object, not in the code object (because they represent values calculated at run-time). Unlike function objects, code objects are immutable and contain no references (directly or indirectly) to mutable objects. <section id="index-60"> <h5>3.2.13.1.1. Special read-only attributes<a class="headerlink" href="#index-60" title="Link to this heading">¶</a></h5> <table class="docutils align-default"> <tbody> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_name"> codeobject.co_name<a class="headerlink" href="#codeobject.co_name" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The function name</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_qualname"> codeobject.co_qualname<a class="headerlink" href="#codeobject.co_qualname" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The fully qualified function name <div class="versionadded"> Added in version 3.11. </div> </td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_argcount"> codeobject.co_argcount<a class="headerlink" href="#codeobject.co_argcount" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The total number of positional <a class="reference internal" href="../glossary.html#term-parameter">parameters</a> (including positional-only parameters and parameters with default values) that the function has</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_posonlyargcount"> codeobject.co_posonlyargcount<a class="headerlink" href="#codeobject.co_posonlyargcount" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The number of positional-only <a class="reference internal" href="../glossary.html#term-parameter">parameters</a> (including arguments with default values) that the function has</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_kwonlyargcount"> codeobject.co_kwonlyargcount<a class="headerlink" href="#codeobject.co_kwonlyargcount" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The number of keyword-only <a class="reference internal" href="../glossary.html#term-parameter">parameters</a> (including arguments with default values) that the function has</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_nlocals"> codeobject.co_nlocals<a class="headerlink" href="#codeobject.co_nlocals" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The number of <a class="reference internal" href="executionmodel.html#naming">local variables</a> used by the function (including parameters)</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_varnames"> codeobject.co_varnames<a class="headerlink" href="#codeobject.co_varnames" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the names of the local variables in the function (starting with the parameter names)</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_cellvars"> codeobject.co_cellvars<a class="headerlink" href="#codeobject.co_cellvars" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the names of <a class="reference internal" href="executionmodel.html#naming">local variables</a> that are referenced from at least one <a class="reference internal" href="../glossary.html#term-nested-scope">nested scope</a> inside the function</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_freevars"> codeobject.co_freevars<a class="headerlink" href="#codeobject.co_freevars" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the names of <a class="reference internal" href="../glossary.html#term-closure-variable">free (closure) variables</a> that a <a class="reference internal" href="../glossary.html#term-nested-scope">nested scope</a> references in an outer scope. See also <a class="reference internal" href="#function.__closure__" title="function.__closure__"><code class="xref py py-attr docutils literal notranslate">function.__closure__</code></a>. Note: references to global and builtin names are not included. </td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_code"> codeobject.co_code<a class="headerlink" href="#codeobject.co_code" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A string representing the sequence of <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> instructions in the function</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_consts"> codeobject.co_consts<a class="headerlink" href="#codeobject.co_consts" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the literals used by the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> in the function</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_names"> codeobject.co_names<a class="headerlink" href="#codeobject.co_names" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> containing the names used by the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> in the function</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_filename"> codeobject.co_filename<a class="headerlink" href="#codeobject.co_filename" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The name of the file from which the code was compiled</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_firstlineno"> codeobject.co_firstlineno<a class="headerlink" href="#codeobject.co_firstlineno" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The line number of the first line of the function</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_lnotab"> codeobject.co_lnotab<a class="headerlink" href="#codeobject.co_lnotab" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>A string encoding the mapping from <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> offsets to line numbers. For details, see the source code of the interpreter. <div class="deprecated"> Deprecated since version 3.12: This attribute of code objects is deprecated, and may be removed in Python 3.15. </div> </td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_stacksize"> codeobject.co_stacksize<a class="headerlink" href="#codeobject.co_stacksize" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The required stack size of the code object</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="codeobject.co_flags"> codeobject.co_flags<a class="headerlink" href="#codeobject.co_flags" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>An <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">integer</code></a> encoding a number of flags for the interpreter.</td> </tr> </tbody> </table> The following flag bits are defined for <a class="reference internal" href="#codeobject.co_flags" title="codeobject.co_flags"><code class="xref py py-attr docutils literal notranslate">co_flags</code></a>: bit <code class="docutils literal notranslate">0x04</code> is set if the function uses the <code class="docutils literal notranslate">*arguments</code> syntax to accept an arbitrary number of positional arguments; bit <code class="docutils literal notranslate">0x08</code> is set if the function uses the <code class="docutils literal notranslate">**keywords</code> syntax to accept arbitrary keyword arguments; bit <code class="docutils literal notranslate">0x20</code> is set if the function is a generator. See <a class="reference internal" href="../library/inspect.html#inspect-module-co-flags">Code Objects Bit Flags</a> for details on the semantics of each flags that might be present. Future feature declarations (<code class="docutils literal notranslate">from __future__ import division</code>) also use bits in <a class="reference internal" href="#codeobject.co_flags" title="codeobject.co_flags"><code class="xref py py-attr docutils literal notranslate">co_flags</code></a> to indicate whether a code object was compiled with a particular feature enabled: bit <code class="docutils literal notranslate">0x2000</code> is set if the function was compiled with future division enabled; bits <code class="docutils literal notranslate">0x10</code> and <code class="docutils literal notranslate">0x1000</code> were used in earlier versions of Python. Other bits in <a class="reference internal" href="#codeobject.co_flags" title="codeobject.co_flags"><code class="xref py py-attr docutils literal notranslate">co_flags</code></a> are reserved for internal use. If a code object represents a function, the first item in <a class="reference internal" href="#codeobject.co_consts" title="codeobject.co_consts"><code class="xref py py-attr docutils literal notranslate">co_consts</code></a> is the documentation string of the function, or <code class="docutils literal notranslate">None</code> if undefined. </section> <section id="methods-on-code-objects"> <h5>3.2.13.1.2. Methods on code objects<a class="headerlink" href="#methods-on-code-objects" title="Link to this heading">¶</a></h5> <dl class="py method"> <dt class="sig sig-object py" id="codeobject.co_positions"> codeobject.co_positions()<a class="headerlink" href="#codeobject.co_positions" title="Link to this definition">¶</a></dt> <dd>Returns an iterable over the source code positions of each <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> instruction in the code object. The iterator returns <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>s containing the <code class="docutils literal notranslate">(start_line, end_line, start_column, end_column)</code>. The i-th tuple corresponds to the position of the source code that compiled to the i-th code unit. Column information is 0-indexed utf-8 byte offsets on the given source line. This positional information can be missing. A non-exhaustive lists of cases where this may happen: <ul class="simple"> <li>Running the interpreter with <a class="reference internal" href="../using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">no_debug_ranges</code>.</li> <li>Loading a pyc file compiled while using <a class="reference internal" href="../using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">no_debug_ranges</code>.</li> <li>Position tuples corresponding to artificial instructions.</li> <li>Line and column numbers that can’t be represented due to implementation specific limitations.</li> </ul> When this occurs, some or all of the tuple elements can be <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate">None</code></a>. <div class="versionadded"> Added in version 3.11. </div> <div class="admonition note"> Note This feature requires storing column positions in code objects which may result in a small increase of disk usage of compiled Python files or interpreter memory usage. To avoid storing the extra information and/or deactivate printing the extra traceback information, the <a class="reference internal" href="../using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X</code></a> <code class="docutils literal notranslate">no_debug_ranges</code> command line flag or the <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONNODEBUGRANGES"><code class="xref std std-envvar docutils literal notranslate">PYTHONNODEBUGRANGES</code></a> environment variable can be used. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="codeobject.co_lines"> codeobject.co_lines()<a class="headerlink" href="#codeobject.co_lines" title="Link to this definition">¶</a></dt> <dd>Returns an iterator that yields information about successive ranges of <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a>s. Each item yielded is a <code class="docutils literal notranslate">(start, end, lineno)</code> <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>: <ul class="simple"> <li><code class="docutils literal notranslate">start</code> (an <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>) represents the offset (inclusive) of the start of the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> range</li> <li><code class="docutils literal notranslate">end</code> (an <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>) represents the offset (exclusive) of the end of the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> range</li> <li><code class="docutils literal notranslate">lineno</code> is an <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> representing the line number of the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> range, or <code class="docutils literal notranslate">None</code> if the bytecodes in the given range have no line number</li> </ul> The items yielded will have the following properties: <ul class="simple"> <li>The first range yielded will have a <code class="docutils literal notranslate">start</code> of 0.</li> <li>The <code class="docutils literal notranslate">(start, end)</code> ranges will be non-decreasing and consecutive. That is, for any pair of <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>s, the <code class="docutils literal notranslate">start</code> of the second will be equal to the <code class="docutils literal notranslate">end</code> of the first.</li> <li>No range will be backwards: <code class="docutils literal notranslate">end >= start</code> for all triples.</li> <li>The last <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> yielded will have <code class="docutils literal notranslate">end</code> equal to the size of the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a>.</li> </ul> Zero-width ranges, where <code class="docutils literal notranslate">start == end</code>, are allowed. Zero-width ranges are used for lines that are present in the source code, but have been eliminated by the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> compiler. <div class="versionadded"> Added in version 3.10. </div> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0626/">PEP 626</a> - Precise line numbers for debugging and other tools.</dt><dd>The PEP that introduced the <code class="xref py py-meth docutils literal notranslate">co_lines()</code> method. </dd> </dl> </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="codeobject.replace"> codeobject.replace(**kwargs)<a class="headerlink" href="#codeobject.replace" title="Link to this definition">¶</a></dt> <dd>Return a copy of the code object with new values for the specified fields. Code objects are also supported by the generic function <a class="reference internal" href="../library/copy.html#copy.replace" title="copy.replace"><code class="xref py py-func docutils literal notranslate">copy.replace()</code></a>. <div class="versionadded"> Added in version 3.8. </div> </dd></dl> </section> </section> <section id="frame-objects"> <h4>3.2.13.2. Frame objects<a class="headerlink" href="#frame-objects" title="Link to this heading">¶</a></h4> Frame objects represent execution frames. They may occur in <a class="reference internal" href="#traceback-objects">traceback objects</a>, and are also passed to registered trace functions. <section id="index-66"> <h5>3.2.13.2.1. Special read-only attributes<a class="headerlink" href="#index-66" title="Link to this heading">¶</a></h5> <table class="docutils align-default"> <tbody> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_back"> frame.f_back<a class="headerlink" href="#frame.f_back" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Points to the previous stack frame (towards the caller), or <code class="docutils literal notranslate">None</code> if this is the bottom stack frame</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_code"> frame.f_code<a class="headerlink" href="#frame.f_code" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The <a class="reference internal" href="#code-objects">code object</a> being executed in this frame. Accessing this attribute raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">object.__getattr__</code> with arguments <code class="docutils literal notranslate">obj</code> and <code class="docutils literal notranslate">"f_code"</code>.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_locals"> frame.f_locals<a class="headerlink" href="#frame.f_locals" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The mapping used by the frame to look up <a class="reference internal" href="executionmodel.html#naming">local variables</a>. If the frame refers to an <a class="reference internal" href="../glossary.html#term-optimized-scope">optimized scope</a>, this may return a write-through proxy object. <div class="versionchanged"> Changed in version 3.13: Return a proxy for optimized scopes. </div> </td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_globals"> frame.f_globals<a class="headerlink" href="#frame.f_globals" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The dictionary used by the frame to look up <a class="reference internal" href="executionmodel.html#naming">global variables</a></td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_builtins"> frame.f_builtins<a class="headerlink" href="#frame.f_builtins" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The dictionary used by the frame to look up <a class="reference internal" href="executionmodel.html#naming">built-in (intrinsic) names</a></td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_lasti"> frame.f_lasti<a class="headerlink" href="#frame.f_lasti" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The “precise instruction” of the frame object (this is an index into the <a class="reference internal" href="../glossary.html#term-bytecode">bytecode</a> string of the <a class="reference internal" href="#code-objects">code object</a>)</td> </tr> </tbody> </table> </section> <section id="index-67"> <h5>3.2.13.2.2. Special writable attributes<a class="headerlink" href="#index-67" title="Link to this heading">¶</a></h5> <table class="docutils align-default"> <tbody> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_trace"> frame.f_trace<a class="headerlink" href="#frame.f_trace" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>If not <code class="docutils literal notranslate">None</code>, this is a function called for various events during code execution (this is used by debuggers). Normally an event is triggered for each new source line (see <a class="reference internal" href="#frame.f_trace_lines" title="frame.f_trace_lines"><code class="xref py py-attr docutils literal notranslate">f_trace_lines</code></a>).</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_trace_lines"> frame.f_trace_lines<a class="headerlink" href="#frame.f_trace_lines" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Set this attribute to <a class="reference internal" href="../library/constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a> to disable triggering a tracing event for each source line.</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_trace_opcodes"> frame.f_trace_opcodes<a class="headerlink" href="#frame.f_trace_opcodes" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Set this attribute to <a class="reference internal" href="../library/constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a> to allow per-opcode events to be requested. Note that this may lead to undefined interpreter behaviour if exceptions raised by the trace function escape to the function being traced.</td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="frame.f_lineno"> frame.f_lineno<a class="headerlink" href="#frame.f_lineno" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>The current line number of the frame – writing to this from within a trace function jumps to the given line (only for the bottom-most frame). A debugger can implement a Jump command (aka Set Next Statement) by writing to this attribute.</td> </tr> </tbody> </table> </section> <section id="frame-object-methods"> <h5>3.2.13.2.3. Frame object methods<a class="headerlink" href="#frame-object-methods" title="Link to this heading">¶</a></h5> Frame objects support one method: <dl class="py method"> <dt class="sig sig-object py" id="frame.clear"> frame.clear()<a class="headerlink" href="#frame.clear" title="Link to this definition">¶</a></dt> <dd>This method clears all references to <a class="reference internal" href="executionmodel.html#naming">local variables</a> held by the frame. Also, if the frame belonged to a <a class="reference internal" href="../glossary.html#term-generator">generator</a>, the generator is finalized. This helps break reference cycles involving frame objects (for example when catching an <a class="reference internal" href="../library/exceptions.html#bltin-exceptions">exception</a> and storing its <a class="reference internal" href="#traceback-objects">traceback</a> for later use). <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> is raised if the frame is currently executing or suspended. <div class="versionadded"> Added in version 3.4. </div> <div class="versionchanged"> Changed in version 3.13: Attempting to clear a suspended frame raises <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> (as has always been the case for executing frames). </div> </dd></dl> </section> </section> <section id="traceback-objects"> <h4>3.2.13.3. Traceback objects<a class="headerlink" href="#traceback-objects" title="Link to this heading">¶</a></h4> Traceback objects represent the stack trace of an <a class="reference internal" href="../tutorial/errors.html#tut-errors">exception</a>. A traceback object is implicitly created when an exception occurs, and may also be explicitly created by calling <a class="reference internal" href="../library/types.html#types.TracebackType" title="types.TracebackType"><code class="xref py py-class docutils literal notranslate">types.TracebackType</code></a>. <div class="versionchanged"> Changed in version 3.7: Traceback objects can now be explicitly instantiated from Python code. </div> For implicitly created tracebacks, when the search for an exception handler unwinds the execution stack, at each unwound level a traceback object is inserted in front of the current traceback. When an exception handler is entered, the stack trace is made available to the program. (See section <a class="reference internal" href="compound_stmts.html#try">The try statement</a>.) It is accessible as the third item of the tuple returned by <a class="reference internal" href="../library/sys.html#sys.exc_info" title="sys.exc_info"><code class="xref py py-func docutils literal notranslate">sys.exc_info()</code></a>, and as the <a class="reference internal" href="../library/exceptions.html#BaseException.__traceback__" title="BaseException.__traceback__"><code class="xref py py-attr docutils literal notranslate">__traceback__</code></a> attribute of the caught exception. When the program contains no suitable handler, the stack trace is written (nicely formatted) to the standard error stream; if the interpreter is interactive, it is also made available to the user as <a class="reference internal" href="../library/sys.html#sys.last_traceback" title="sys.last_traceback"><code class="xref py py-data docutils literal notranslate">sys.last_traceback</code></a>. For explicitly created tracebacks, it is up to the creator of the traceback to determine how the <a class="reference internal" href="#traceback.tb_next" title="traceback.tb_next"><code class="xref py py-attr docutils literal notranslate">tb_next</code></a> attributes should be linked to form a full stack trace. Special read-only attributes: <table class="docutils align-default"> <tbody> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="traceback.tb_frame"> traceback.tb_frame<a class="headerlink" href="#traceback.tb_frame" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Points to the execution <a class="reference internal" href="#frame-objects">frame</a> of the current level. Accessing this attribute raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">object.__getattr__</code> with arguments <code class="docutils literal notranslate">obj</code> and <code class="docutils literal notranslate">"tb_frame"</code>. </td> </tr> <tr class="row-even"><td><dl class="py attribute"> <dt class="sig sig-object py" id="traceback.tb_lineno"> traceback.tb_lineno<a class="headerlink" href="#traceback.tb_lineno" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Gives the line number where the exception occurred</td> </tr> <tr class="row-odd"><td><dl class="py attribute"> <dt class="sig sig-object py" id="traceback.tb_lasti"> traceback.tb_lasti<a class="headerlink" href="#traceback.tb_lasti" title="Link to this definition">¶</a></dt> <dd></dd></dl> </td> <td>Indicates the “precise instruction”.</td> </tr> </tbody> </table> The line number and last instruction in the traceback may differ from the line number of its <a class="reference internal" href="#frame-objects">frame object</a> if the exception occurred in a <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate">try</code></a> statement with no matching except clause or with a <a class="reference internal" href="compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate">finally</code></a> clause. <dl class="py attribute" id="index-70"> <dt class="sig sig-object py" id="traceback.tb_next"> traceback.tb_next<a class="headerlink" href="#traceback.tb_next" title="Link to this definition">¶</a></dt> <dd>The special writable attribute <code class="xref py py-attr docutils literal notranslate">tb_next</code> is the next level in the stack trace (towards the frame where the exception occurred), or <code class="docutils literal notranslate">None</code> if there is no next level. <div class="versionchanged"> Changed in version 3.7: This attribute is now writable </div> </dd></dl> </section> <section id="slice-objects"> <h4>3.2.13.4. Slice objects<a class="headerlink" href="#slice-objects" title="Link to this heading">¶</a></h4> Slice objects are used to represent slices for <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> methods. They are also created by the built-in <a class="reference internal" href="../library/functions.html#slice" title="slice"><code class="xref py py-func docutils literal notranslate">slice()</code></a> function. Special read-only attributes: <a class="reference internal" href="../library/functions.html#slice.start" title="slice.start"><code class="xref py py-attr docutils literal notranslate">start</code></a> is the lower bound; <a class="reference internal" href="../library/functions.html#slice.stop" title="slice.stop"><code class="xref py py-attr docutils literal notranslate">stop</code></a> is the upper bound; <a class="reference internal" href="../library/functions.html#slice.step" title="slice.step"><code class="xref py py-attr docutils literal notranslate">step</code></a> is the step value; each is <code class="docutils literal notranslate">None</code> if omitted. These attributes can have any type. Slice objects support one method: <dl class="py method"> <dt class="sig sig-object py" id="slice.indices"> slice.indices(self, length)<a class="headerlink" href="#slice.indices" title="Link to this definition">¶</a></dt> <dd>This method takes a single integer argument length and computes information about the slice that the slice object would describe if applied to a sequence of length items. It returns a tuple of three integers; respectively these are the start and stop indices and the step or stride length of the slice. Missing or out-of-bounds indices are handled in a manner consistent with regular slices. </dd></dl> </section> <section id="static-method-objects"> <h4>3.2.13.5. Static method objects<a class="headerlink" href="#static-method-objects" title="Link to this heading">¶</a></h4> Static method objects provide a way of defeating the transformation of function objects to method objects described above. A static method object is a wrapper around any other object, usually a user-defined method object. When a static method object is retrieved from a class or a class instance, the object actually returned is the wrapped object, which is not subject to any further transformation. Static method objects are also callable. Static method objects are created by the built-in <a class="reference internal" href="../library/functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate">staticmethod()</code></a> constructor. </section> <section id="class-method-objects"> <h4>3.2.13.6. Class method objects<a class="headerlink" href="#class-method-objects" title="Link to this heading">¶</a></h4> A class method object, like a static method object, is a wrapper around another object that alters the way in which that object is retrieved from classes and class instances. The behaviour of class method objects upon such retrieval is described above, under <a class="reference internal" href="#instance-methods">“instance methods”</a>. Class method objects are created by the built-in <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate">classmethod()</code></a> constructor. </section> </section> </section> <section id="special-method-names"> <h2>3.3. Special method names<a class="headerlink" href="#special-method-names" title="Link to this heading">¶</a></h2> A class can implement certain operations that are invoked by special syntax (such as arithmetic operations or subscripting and slicing) by defining methods with special names. This is Python’s approach to operator overloading, allowing classes to define their own behavior with respect to language operators. For instance, if a class defines a method named <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>, and <code class="docutils literal notranslate">x</code> is an instance of this class, then <code class="docutils literal notranslate">x[i]</code> is roughly equivalent to <code class="docutils literal notranslate">type(x).__getitem__(x, i)</code>. Except where mentioned, attempts to execute an operation raise an exception when no appropriate method is defined (typically <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>). Setting a special method to <code class="docutils literal notranslate">None</code> indicates that the corresponding operation is not available. For example, if a class sets <a class="reference internal" href="#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a> to <code class="docutils literal notranslate">None</code>, the class is not iterable, so calling <a class="reference internal" href="../library/functions.html#iter" title="iter"><code class="xref py py-func docutils literal notranslate">iter()</code></a> on its instances will raise a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> (without falling back to <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>). <a class="footnote-reference brackets" href="#id20" id="id12" role="doc-noteref">[2]</a> When implementing a class that emulates any built-in type, it is important that the emulation only be implemented to the degree that it makes sense for the object being modelled. For example, some sequences may work well with retrieval of individual elements, but extracting a slice may not make sense. (One example of this is the <code class="xref py py-class docutils literal notranslate">NodeList</code> interface in the W3C’s Document Object Model.) <section id="basic-customization"> <h3>3.3.1. Basic customization<a class="headerlink" href="#basic-customization" title="Link to this heading">¶</a></h3> <dl class="py method"> <dt class="sig sig-object py" id="object.__new__"> object.__new__(cls[, ...])<a class="headerlink" href="#object.__new__" title="Link to this definition">¶</a></dt> <dd>Called to create a new instance of class cls. <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> is a static method (special-cased so you need not declare it as such) that takes the class of which an instance was requested as its first argument. The remaining arguments are those passed to the object constructor expression (the call to the class). The return value of <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> should be the new object instance (usually an instance of cls). Typical implementations create a new instance of the class by invoking the superclass’s <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> method using <code class="docutils literal notranslate">super().__new__(cls[, ...])</code> with appropriate arguments and then modifying the newly created instance as necessary before returning it. If <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> is invoked during object construction and it returns an instance of cls, then the new instance’s <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> method will be invoked like <code class="docutils literal notranslate">__init__(self[, ...])</code>, where self is the new instance and the remaining arguments are the same as were passed to the object constructor. If <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> does not return an instance of cls, then the new instance’s <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> method will not be invoked. <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> is intended mainly to allow subclasses of immutable types (like int, str, or tuple) to customize instance creation. It is also commonly overridden in custom metaclasses in order to customize class creation. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__init__"> object.__init__(self[, ...])<a class="headerlink" href="#object.__init__" title="Link to this definition">¶</a></dt> <dd>Called after the instance has been created (by <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a>), but before it is returned to the caller. The arguments are those passed to the class constructor expression. If a base class has an <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> method, the derived class’s <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> method, if any, must explicitly call it to ensure proper initialization of the base class part of the instance; for example: <code class="docutils literal notranslate">super().__init__([args...])</code>. Because <a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> and <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> work together in constructing objects (<a class="reference internal" href="#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</code></a> to create it, and <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> to customize it), no non-<code class="docutils literal notranslate">None</code> value may be returned by <a class="reference internal" href="#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a>; doing so will cause a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> to be raised at runtime. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__del__"> object.__del__(self)<a class="headerlink" href="#object.__del__" title="Link to this definition">¶</a></dt> <dd>Called when the instance is about to be destroyed. This is also called a finalizer or (improperly) a destructor. If a base class has a <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> method, the derived class’s <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> method, if any, must explicitly call it to ensure proper deletion of the base class part of the instance. It is possible (though not recommended!) for the <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> method to postpone destruction of the instance by creating a new reference to it. This is called object resurrection. It is implementation-dependent whether <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> is called a second time when a resurrected object is about to be destroyed; the current <a class="reference internal" href="../glossary.html#term-CPython">CPython</a> implementation only calls it once. It is not guaranteed that <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> methods are called for objects that still exist when the interpreter exits. <a class="reference internal" href="../library/weakref.html#weakref.finalize" title="weakref.finalize"><code class="xref py py-class docutils literal notranslate">weakref.finalize</code></a> provides a straightforward way to register a cleanup function to be called when an object is garbage collected. <div class="admonition note"> Note <code class="docutils literal notranslate">del x</code> doesn’t directly call <code class="docutils literal notranslate">x.__del__()</code> — the former decrements the reference count for <code class="docutils literal notranslate">x</code> by one, and the latter is only called when <code class="docutils literal notranslate">x</code>’s reference count reaches zero. </div> <div class="impl-detail compound"> CPython implementation detail: It is possible for a reference cycle to prevent the reference count of an object from going to zero. In this case, the cycle will be later detected and deleted by the <a class="reference internal" href="../glossary.html#term-garbage-collection">cyclic garbage collector</a>. A common cause of reference cycles is when an exception has been caught in a local variable. The frame’s locals then reference the exception, which references its own traceback, which references the locals of all frames caught in the traceback. <div class="admonition seealso"> See also Documentation for the <a class="reference internal" href="../library/gc.html#module-gc" title="gc: Interface to the cycle-detecting garbage collector."><code class="xref py py-mod docutils literal notranslate">gc</code></a> module. </div> </div> <div class="admonition warning"> Warning Due to the precarious circumstances under which <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> methods are invoked, exceptions that occur during their execution are ignored, and a warning is printed to <code class="docutils literal notranslate">sys.stderr</code> instead. In particular: <ul class="simple"> <li><a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> can be invoked when arbitrary code is being executed, including from any arbitrary thread. If <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> needs to take a lock or invoke any other blocking resource, it may deadlock as the resource may already be taken by the code that gets interrupted to execute <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a>.</li> <li><a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> can be executed during interpreter shutdown. As a consequence, the global variables it needs to access (including other modules) may already have been deleted or set to <code class="docutils literal notranslate">None</code>. Python guarantees that globals whose name begins with a single underscore are deleted from their module before other globals are deleted; if no other references to such globals exist, this may help in assuring that imported modules are still available at the time when the <a class="reference internal" href="#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate">__del__()</code></a> method is called.</li> </ul> </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__repr__"> object.__repr__(self)<a class="headerlink" href="#object.__repr__" title="Link to this definition">¶</a></dt> <dd>Called by the <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate">repr()</code></a> built-in function to compute the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form <code class="docutils literal notranslate"><...some useful description...></code> should be returned. The return value must be a string object. If a class defines <a class="reference internal" href="#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate">__repr__()</code></a> but not <a class="reference internal" href="#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate">__str__()</code></a>, then <a class="reference internal" href="#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate">__repr__()</code></a> is also used when an “informal” string representation of instances of that class is required. This is typically used for debugging, so it is important that the representation is information-rich and unambiguous. A default implementation is provided by the <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__str__"> object.__str__(self)<a class="headerlink" href="#object.__str__" title="Link to this definition">¶</a></dt> <dd>Called by <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate">str(object)</code></a>, the default <a class="reference internal" href="#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate">__format__()</code></a> implementation, and the built-in function <a class="reference internal" href="../library/functions.html#print" title="print"><code class="xref py py-func docutils literal notranslate">print()</code></a>, to compute the “informal” or nicely printable string representation of an object. The return value must be a <a class="reference internal" href="../library/stdtypes.html#textseq">str</a> object. This method differs from <a class="reference internal" href="#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate">object.__repr__()</code></a> in that there is no expectation that <a class="reference internal" href="#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate">__str__()</code></a> return a valid Python expression: a more convenient or concise representation can be used. The default implementation defined by the built-in type <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> calls <a class="reference internal" href="#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate">object.__repr__()</code></a>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__bytes__"> object.__bytes__(self)<a class="headerlink" href="#object.__bytes__" title="Link to this definition">¶</a></dt> <dd>Called by <a class="reference internal" href="../library/functions.html#func-bytes">bytes</a> to compute a byte-string representation of an object. This should return a <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> object. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not provide this method. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__format__"> object.__format__(self, format_spec)<a class="headerlink" href="#object.__format__" title="Link to this definition">¶</a></dt> <dd>Called by the <a class="reference internal" href="../library/functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate">format()</code></a> built-in function, and by extension, evaluation of <a class="reference internal" href="lexical_analysis.html#f-strings">formatted string literals</a> and the <a class="reference internal" href="../library/stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">str.format()</code></a> method, to produce a “formatted” string representation of an object. The format_spec argument is a string that contains a description of the formatting options desired. The interpretation of the format_spec argument is up to the type implementing <a class="reference internal" href="#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate">__format__()</code></a>, however most classes will either delegate formatting to one of the built-in types, or use a similar formatting option syntax. See <a class="reference internal" href="../library/string.html#formatspec">Format Specification Mini-Language</a> for a description of the standard formatting syntax. The return value must be a string object. The default implementation by the <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class should be given an empty format_spec string. It delegates to <a class="reference internal" href="#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate">__str__()</code></a>. <div class="versionchanged"> Changed in version 3.4: The __format__ method of <code class="docutils literal notranslate">object</code> itself raises a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> if passed any non-empty string. </div> <div class="versionchanged"> Changed in version 3.7: <code class="docutils literal notranslate">object.__format__(x, '')</code> is now equivalent to <code class="docutils literal notranslate">str(x)</code> rather than <code class="docutils literal notranslate">format(str(x), '')</code>. </div> </dd></dl> <dl class="py method" id="richcmpfuncs"> <dt class="sig sig-object py" id="object.__lt__"> object.__lt__(self, other)<a class="headerlink" href="#object.__lt__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__le__"> object.__le__(self, other)<a class="headerlink" href="#object.__le__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__eq__"> object.__eq__(self, other)<a class="headerlink" href="#object.__eq__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ne__"> object.__ne__(self, other)<a class="headerlink" href="#object.__ne__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__gt__"> object.__gt__(self, other)<a class="headerlink" href="#object.__gt__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ge__"> object.__ge__(self, other)<a class="headerlink" href="#object.__ge__" title="Link to this definition">¶</a></dt> <dd>These are the so-called “rich comparison” methods. The correspondence between operator symbols and method names is as follows: <code class="docutils literal notranslate">x<y</code> calls <code class="docutils literal notranslate">x.__lt__(y)</code>, <code class="docutils literal notranslate">x<=y</code> calls <code class="docutils literal notranslate">x.__le__(y)</code>, <code class="docutils literal notranslate">x==y</code> calls <code class="docutils literal notranslate">x.__eq__(y)</code>, <code class="docutils literal notranslate">x!=y</code> calls <code class="docutils literal notranslate">x.__ne__(y)</code>, <code class="docutils literal notranslate">x>y</code> calls <code class="docutils literal notranslate">x.__gt__(y)</code>, and <code class="docutils literal notranslate">x>=y</code> calls <code class="docutils literal notranslate">x.__ge__(y)</code>. A rich comparison method may return the singleton <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a> if it does not implement the operation for a given pair of arguments. By convention, <code class="docutils literal notranslate">False</code> and <code class="docutils literal notranslate">True</code> are returned for a successful comparison. However, these methods can return any value, so if the comparison operator is used in a Boolean context (e.g., in the condition of an <code class="docutils literal notranslate">if</code> statement), Python will call <a class="reference internal" href="../library/functions.html#bool" title="bool"><code class="xref py py-func docutils literal notranslate">bool()</code></a> on the value to determine if the result is true or false. By default, <code class="docutils literal notranslate">object</code> implements <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> by using <code class="docutils literal notranslate">is</code>, returning <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a> in the case of a false comparison: <code class="docutils literal notranslate">True if x is y else NotImplemented</code>. For <a class="reference internal" href="#object.__ne__" title="object.__ne__"><code class="xref py py-meth docutils literal notranslate">__ne__()</code></a>, by default it delegates to <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> and inverts the result unless it is <code class="xref py py-data docutils literal notranslate">NotImplemented</code>. There are no other implied relationships among the comparison operators or default implementations; for example, the truth of <code class="docutils literal notranslate">(x<y or x==y)</code> does not imply <code class="docutils literal notranslate">x<=y</code>. To automatically generate ordering operations from a single root operation, see <a class="reference internal" href="../library/functools.html#functools.total_ordering" title="functools.total_ordering"><code class="xref py py-func docutils literal notranslate">functools.total_ordering()</code></a>. By default, the <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class provides implementations consistent with <a class="reference internal" href="expressions.html#expressions-value-comparisons">Value comparisons</a>: equality compares according to object identity, and order comparisons raise <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>. Each default method may generate these results directly, but may also return <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>. See the paragraph on <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> for some important notes on creating <a class="reference internal" href="../glossary.html#term-hashable">hashable</a> objects which support custom comparison operations and are usable as dictionary keys. There are no swapped-argument versions of these methods (to be used when the left argument does not support the operation but the right argument does); rather, <a class="reference internal" href="#object.__lt__" title="object.__lt__"><code class="xref py py-meth docutils literal notranslate">__lt__()</code></a> and <a class="reference internal" href="#object.__gt__" title="object.__gt__"><code class="xref py py-meth docutils literal notranslate">__gt__()</code></a> are each other’s reflection, <a class="reference internal" href="#object.__le__" title="object.__le__"><code class="xref py py-meth docutils literal notranslate">__le__()</code></a> and <a class="reference internal" href="#object.__ge__" title="object.__ge__"><code class="xref py py-meth docutils literal notranslate">__ge__()</code></a> are each other’s reflection, and <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> and <a class="reference internal" href="#object.__ne__" title="object.__ne__"><code class="xref py py-meth docutils literal notranslate">__ne__()</code></a> are their own reflection. If the operands are of different types, and the right operand’s type is a direct or indirect subclass of the left operand’s type, the reflected method of the right operand has priority, otherwise the left operand’s method has priority. Virtual subclassing is not considered. When no appropriate method returns any value other than <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>, the <code class="docutils literal notranslate">==</code> and <code class="docutils literal notranslate">!=</code> operators will fall back to <code class="docutils literal notranslate">is</code> and <code class="docutils literal notranslate">is not</code>, respectively. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__hash__"> object.__hash__(self)<a class="headerlink" href="#object.__hash__" title="Link to this definition">¶</a></dt> <dd>Called by built-in function <a class="reference internal" href="../library/functions.html#hash" title="hash"><code class="xref py py-func docutils literal notranslate">hash()</code></a> and for operations on members of hashed collections including <a class="reference internal" href="../library/stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set</code></a>, <a class="reference internal" href="../library/stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a>, and <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>. The <code class="docutils literal notranslate">__hash__()</code> method should return an integer. The only required property is that objects which compare equal have the same hash value; it is advised to mix together the hash values of the components of the object that also play a part in comparison of objects by packing them into a tuple and hashing the tuple. Example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def __hash__(self): return hash((self.name, self.nick, self.color)) </pre></div> </div> <div class="admonition note"> Note <a class="reference internal" href="../library/functions.html#hash" title="hash"><code class="xref py py-func docutils literal notranslate">hash()</code></a> truncates the value returned from an object’s custom <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> method to the size of a <a class="reference internal" href="../c-api/intro.html#c.Py_ssize_t" title="Py_ssize_t"><code class="xref c c-type docutils literal notranslate">Py_ssize_t</code></a>. This is typically 8 bytes on 64-bit builds and 4 bytes on 32-bit builds. If an object’s <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> must interoperate on builds of different bit sizes, be sure to check the width on all supported builds. An easy way to do this is with <code class="docutils literal notranslate">python -c "import sys; print(sys.hash_info.width)"</code>. </div> If a class does not define an <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> method it should not define a <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> operation either; if it defines <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> but not <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a>, its instances will not be usable as items in hashable collections. If a class defines mutable objects and implements an <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> method, it should not implement <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a>, since the implementation of <a class="reference internal" href="../glossary.html#term-hashable">hashable</a> collections requires that a key’s hash value is immutable (if the object’s hash value changes, it will be in the wrong hash bucket). User-defined classes have <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> and <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> methods by default (inherited from the <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class); with them, all objects compare unequal (except with themselves) and <code class="docutils literal notranslate">x.__hash__()</code> returns an appropriate value such that <code class="docutils literal notranslate">x == y</code> implies both that <code class="docutils literal notranslate">x is y</code> and <code class="docutils literal notranslate">hash(x) == hash(y)</code>. A class that overrides <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> and does not define <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> will have its <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> implicitly set to <code class="docutils literal notranslate">None</code>. When the <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> method of a class is <code class="docutils literal notranslate">None</code>, instances of the class will raise an appropriate <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> when a program attempts to retrieve their hash value, and will also be correctly identified as unhashable when checking <code class="docutils literal notranslate">isinstance(obj, collections.abc.Hashable)</code>. If a class that overrides <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> needs to retain the implementation of <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> from a parent class, the interpreter must be told this explicitly by setting <code class="docutils literal notranslate">__hash__ = <ParentClass>.__hash__</code>. If a class that does not override <a class="reference internal" href="#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> wishes to suppress hash support, it should include <code class="docutils literal notranslate">__hash__ = None</code> in the class definition. A class which defines its own <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> that explicitly raises a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> would be incorrectly identified as hashable by an <code class="docutils literal notranslate">isinstance(obj, collections.abc.Hashable)</code> call. <div class="admonition note"> Note By default, the <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> values of str and bytes objects are “salted” with an unpredictable random value. Although they remain constant within an individual Python process, they are not predictable between repeated invocations of Python. This is intended to provide protection against a denial-of-service caused by carefully chosen inputs that exploit the worst case performance of a dict insertion, O(n2) complexity. See <a class="reference external" href="http://ocert.org/advisories/ocert-2011-003.html">http://ocert.org/advisories/ocert-2011-003.html</a> for details. Changing hash values affects the iteration order of sets. Python has never made guarantees about this ordering (and it typically varies between 32-bit and 64-bit builds). See also <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONHASHSEED"><code class="xref std std-envvar docutils literal notranslate">PYTHONHASHSEED</code></a>. </div> <div class="versionchanged"> Changed in version 3.3: Hash randomization is enabled by default. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__bool__"> object.__bool__(self)<a class="headerlink" href="#object.__bool__" title="Link to this definition">¶</a></dt> <dd>Called to implement truth value testing and the built-in operation <code class="docutils literal notranslate">bool()</code>; should return <code class="docutils literal notranslate">False</code> or <code class="docutils literal notranslate">True</code>. When this method is not defined, <a class="reference internal" href="#object.__len__" title="object.__len__"><code class="xref py py-meth docutils literal notranslate">__len__()</code></a> is called, if it is defined, and the object is considered true if its result is nonzero. If a class defines neither <code class="xref py py-meth docutils literal notranslate">__len__()</code> nor <code class="xref py py-meth docutils literal notranslate">__bool__()</code> (which is true of the <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself), all its instances are considered true. </dd></dl> </section> <section id="customizing-attribute-access"> <h3>3.3.2. Customizing attribute access<a class="headerlink" href="#customizing-attribute-access" title="Link to this heading">¶</a></h3> The following methods can be defined to customize the meaning of attribute access (use of, assignment to, or deletion of <code class="docutils literal notranslate">x.name</code>) for class instances. <dl class="py method"> <dt class="sig sig-object py" id="object.__getattr__"> object.__getattr__(self, name)<a class="headerlink" href="#object.__getattr__" title="Link to this definition">¶</a></dt> <dd>Called when the default attribute access fails with an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> (either <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a> raises an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> because name is not an instance attribute or an attribute in the class tree for <code class="docutils literal notranslate">self</code>; or <a class="reference internal" href="#object.__get__" title="object.__get__"><code class="xref py py-meth docutils literal notranslate">__get__()</code></a> of a name property raises <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>). This method should either return the (computed) attribute value or raise an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> exception. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not provide this method. Note that if the attribute is found through the normal mechanism, <a class="reference internal" href="#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate">__getattr__()</code></a> is not called. (This is an intentional asymmetry between <a class="reference internal" href="#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate">__getattr__()</code></a> and <a class="reference internal" href="#object.__setattr__" title="object.__setattr__"><code class="xref py py-meth docutils literal notranslate">__setattr__()</code></a>.) This is done both for efficiency reasons and because otherwise <a class="reference internal" href="#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate">__getattr__()</code></a> would have no way to access other attributes of the instance. Note that at least for instance variables, you can take total control by not inserting any values in the instance attribute dictionary (but instead inserting them in another object). See the <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a> method below for a way to actually get total control over attribute access. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__getattribute__"> object.__getattribute__(self, name)<a class="headerlink" href="#object.__getattribute__" title="Link to this definition">¶</a></dt> <dd>Called unconditionally to implement attribute accesses for instances of the class. If the class also defines <a class="reference internal" href="#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate">__getattr__()</code></a>, the latter will not be called unless <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a> either calls it explicitly or raises an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. This method should return the (computed) attribute value or raise an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> exception. In order to avoid infinite recursion in this method, its implementation should always call the base class method with the same name to access any attributes it needs, for example, <code class="docutils literal notranslate">object.__getattribute__(self, name)</code>. <div class="admonition note"> Note This method may still be bypassed when looking up special methods as the result of implicit invocation via language syntax or <a class="reference internal" href="#builtin-functions">built-in functions</a>. See <a class="reference internal" href="#special-lookup">Special method lookup</a>. </div> For certain sensitive attribute accesses, raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">object.__getattr__</code> with arguments <code class="docutils literal notranslate">obj</code> and <code class="docutils literal notranslate">name</code>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__setattr__"> object.__setattr__(self, name, value)<a class="headerlink" href="#object.__setattr__" title="Link to this definition">¶</a></dt> <dd>Called when an attribute assignment is attempted. This is called instead of the normal mechanism (i.e. store the value in the instance dictionary). name is the attribute name, value is the value to be assigned to it. If <a class="reference internal" href="#object.__setattr__" title="object.__setattr__"><code class="xref py py-meth docutils literal notranslate">__setattr__()</code></a> wants to assign to an instance attribute, it should call the base class method with the same name, for example, <code class="docutils literal notranslate">object.__setattr__(self, name, value)</code>. For certain sensitive attribute assignments, raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">object.__setattr__</code> with arguments <code class="docutils literal notranslate">obj</code>, <code class="docutils literal notranslate">name</code>, <code class="docutils literal notranslate">value</code>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__delattr__"> object.__delattr__(self, name)<a class="headerlink" href="#object.__delattr__" title="Link to this definition">¶</a></dt> <dd>Like <a class="reference internal" href="#object.__setattr__" title="object.__setattr__"><code class="xref py py-meth docutils literal notranslate">__setattr__()</code></a> but for attribute deletion instead of assignment. This should only be implemented if <code class="docutils literal notranslate">del obj.name</code> is meaningful for the object. For certain sensitive attribute deletions, raises an <a class="reference internal" href="../library/sys.html#auditing">auditing event</a> <code class="docutils literal notranslate">object.__delattr__</code> with arguments <code class="docutils literal notranslate">obj</code> and <code class="docutils literal notranslate">name</code>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__dir__"> object.__dir__(self)<a class="headerlink" href="#object.__dir__" title="Link to this definition">¶</a></dt> <dd>Called when <a class="reference internal" href="../library/functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate">dir()</code></a> is called on the object. An iterable must be returned. <a class="reference internal" href="../library/functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate">dir()</code></a> converts the returned iterable to a list and sorts it. </dd></dl> <section id="customizing-module-attribute-access"> <h4>3.3.2.1. Customizing module attribute access<a class="headerlink" href="#customizing-module-attribute-access" title="Link to this heading">¶</a></h4> Special names <code class="docutils literal notranslate">__getattr__</code> and <code class="docutils literal notranslate">__dir__</code> can be also used to customize access to module attributes. The <code class="docutils literal notranslate">__getattr__</code> function at the module level should accept one argument which is the name of an attribute and return the computed value or raise an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. If an attribute is not found on a module object through the normal lookup, i.e. <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">object.__getattribute__()</code></a>, then <code class="docutils literal notranslate">__getattr__</code> is searched in the module <code class="docutils literal notranslate">__dict__</code> before raising an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. If found, it is called with the attribute name and the result is returned. The <code class="docutils literal notranslate">__dir__</code> function should accept no arguments, and return an iterable of strings that represents the names accessible on module. If present, this function overrides the standard <a class="reference internal" href="../library/functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate">dir()</code></a> search on a module. For a more fine grained customization of the module behavior (setting attributes, properties, etc.), one can set the <code class="docutils literal notranslate">__class__</code> attribute of a module object to a subclass of <a class="reference internal" href="../library/types.html#types.ModuleType" title="types.ModuleType"><code class="xref py py-class docutils literal notranslate">types.ModuleType</code></a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>import sys from types import ModuleType class VerboseModule(ModuleType): def __repr__(self): return f'Verbose {self.__name__}' def __setattr__(self, attr, value): print(f'Setting {attr}...') super().__setattr__(attr, value) sys.modules[__name__].__class__ = VerboseModule </pre></div> </div> <div class="admonition note"> Note Defining module <code class="docutils literal notranslate">__getattr__</code> and setting module <code class="docutils literal notranslate">__class__</code> only affect lookups made using the attribute access syntax – directly accessing the module globals (whether by code within the module, or via a reference to the module’s globals dictionary) is unaffected. </div> <div class="versionchanged"> Changed in version 3.5: <code class="docutils literal notranslate">__class__</code> module attribute is now writable. </div> <div class="versionadded"> Added in version 3.7: <code class="docutils literal notranslate">__getattr__</code> and <code class="docutils literal notranslate">__dir__</code> module attributes. </div> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0562/">PEP 562</a> - Module __getattr__ and __dir__</dt><dd>Describes the <code class="docutils literal notranslate">__getattr__</code> and <code class="docutils literal notranslate">__dir__</code> functions on modules. </dd> </dl> </div> </section> <section id="implementing-descriptors"> <h4>3.3.2.2. Implementing Descriptors<a class="headerlink" href="#implementing-descriptors" title="Link to this heading">¶</a></h4> The following methods only apply when an instance of the class containing the method (a so-called descriptor class) appears in an owner class (the descriptor must be in either the owner’s class dictionary or in the class dictionary for one of its parents). In the examples below, “the attribute” refers to the attribute whose name is the key of the property in the owner class’ <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a>. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not implement any of these protocols. <dl class="py method"> <dt class="sig sig-object py" id="object.__get__"> object.__get__(self, instance, owner=None)<a class="headerlink" href="#object.__get__" title="Link to this definition">¶</a></dt> <dd>Called to get the attribute of the owner class (class attribute access) or of an instance of that class (instance attribute access). The optional owner argument is the owner class, while instance is the instance that the attribute was accessed through, or <code class="docutils literal notranslate">None</code> when the attribute is accessed through the owner. This method should return the computed attribute value or raise an <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> exception. <a class="pep reference external" href="https://peps.python.org/pep-0252/">PEP 252</a> specifies that <a class="reference internal" href="#object.__get__" title="object.__get__"><code class="xref py py-meth docutils literal notranslate">__get__()</code></a> is callable with one or two arguments. Python’s own built-in descriptors support this specification; however, it is likely that some third-party tools have descriptors that require both arguments. Python’s own <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a> implementation always passes in both arguments whether they are required or not. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__set__"> object.__set__(self, instance, value)<a class="headerlink" href="#object.__set__" title="Link to this definition">¶</a></dt> <dd>Called to set the attribute on an instance instance of the owner class to a new value, value. Note, adding <a class="reference internal" href="#object.__set__" title="object.__set__"><code class="xref py py-meth docutils literal notranslate">__set__()</code></a> or <a class="reference internal" href="#object.__delete__" title="object.__delete__"><code class="xref py py-meth docutils literal notranslate">__delete__()</code></a> changes the kind of descriptor to a “data descriptor”. See <a class="reference internal" href="#descriptor-invocation">Invoking Descriptors</a> for more details. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__delete__"> object.__delete__(self, instance)<a class="headerlink" href="#object.__delete__" title="Link to this definition">¶</a></dt> <dd>Called to delete the attribute on an instance instance of the owner class. </dd></dl> Instances of descriptors may also have the <code class="xref py py-attr docutils literal notranslate">__objclass__</code> attribute present: <dl class="py attribute"> <dt class="sig sig-object py" id="object.__objclass__"> object.__objclass__<a class="headerlink" href="#object.__objclass__" title="Link to this definition">¶</a></dt> <dd>The attribute <code class="xref py py-attr docutils literal notranslate">__objclass__</code> is interpreted by the <a class="reference internal" href="../library/inspect.html#module-inspect" title="inspect: Extract information and source code from live objects."><code class="xref py py-mod docutils literal notranslate">inspect</code></a> module as specifying the class where this object was defined (setting this appropriately can assist in runtime introspection of dynamic class attributes). For callables, it may indicate that an instance of the given type (or a subclass) is expected or required as the first positional argument (for example, CPython sets this attribute for unbound methods that are implemented in C). </dd></dl> </section> <section id="invoking-descriptors"> <h4>3.3.2.3. Invoking Descriptors<a class="headerlink" href="#invoking-descriptors" title="Link to this heading">¶</a></h4> In general, a descriptor is an object attribute with “binding behavior”, one whose attribute access has been overridden by methods in the descriptor protocol: <a class="reference internal" href="#object.__get__" title="object.__get__"><code class="xref py py-meth docutils literal notranslate">__get__()</code></a>, <a class="reference internal" href="#object.__set__" title="object.__set__"><code class="xref py py-meth docutils literal notranslate">__set__()</code></a>, and <a class="reference internal" href="#object.__delete__" title="object.__delete__"><code class="xref py py-meth docutils literal notranslate">__delete__()</code></a>. If any of those methods are defined for an object, it is said to be a descriptor. The default behavior for attribute access is to get, set, or delete the attribute from an object’s dictionary. For instance, <code class="docutils literal notranslate">a.x</code> has a lookup chain starting with <code class="docutils literal notranslate">a.__dict__['x']</code>, then <code class="docutils literal notranslate">type(a).__dict__['x']</code>, and continuing through the base classes of <code class="docutils literal notranslate">type(a)</code> excluding metaclasses. However, if the looked-up value is an object defining one of the descriptor methods, then Python may override the default behavior and invoke the descriptor method instead. Where this occurs in the precedence chain depends on which descriptor methods were defined and how they were called. The starting point for descriptor invocation is a binding, <code class="docutils literal notranslate">a.x</code>. How the arguments are assembled depends on <code class="docutils literal notranslate">a</code>: <dl class="simple"> <dt>Direct Call</dt><dd>The simplest and least common call is when user code directly invokes a descriptor method: <code class="docutils literal notranslate">x.__get__(a)</code>. </dd> <dt>Instance Binding</dt><dd>If binding to an object instance, <code class="docutils literal notranslate">a.x</code> is transformed into the call: <code class="docutils literal notranslate">type(a).__dict__['x'].__get__(a, type(a))</code>. </dd> <dt>Class Binding</dt><dd>If binding to a class, <code class="docutils literal notranslate">A.x</code> is transformed into the call: <code class="docutils literal notranslate">A.__dict__['x'].__get__(None, A)</code>. </dd> <dt>Super Binding</dt><dd>A dotted lookup such as <code class="docutils literal notranslate">super(A, a).x</code> searches <code class="docutils literal notranslate">a.__class__.__mro__</code> for a base class <code class="docutils literal notranslate">B</code> following <code class="docutils literal notranslate">A</code> and then returns <code class="docutils literal notranslate">B.__dict__['x'].__get__(a, A)</code>. If not a descriptor, <code class="docutils literal notranslate">x</code> is returned unchanged. </dd> </dl> For instance bindings, the precedence of descriptor invocation depends on which descriptor methods are defined. A descriptor can define any combination of <a class="reference internal" href="#object.__get__" title="object.__get__"><code class="xref py py-meth docutils literal notranslate">__get__()</code></a>, <a class="reference internal" href="#object.__set__" title="object.__set__"><code class="xref py py-meth docutils literal notranslate">__set__()</code></a> and <a class="reference internal" href="#object.__delete__" title="object.__delete__"><code class="xref py py-meth docutils literal notranslate">__delete__()</code></a>. If it does not define <code class="xref py py-meth docutils literal notranslate">__get__()</code>, then accessing the attribute will return the descriptor object itself unless there is a value in the object’s instance dictionary. If the descriptor defines <code class="xref py py-meth docutils literal notranslate">__set__()</code> and/or <code class="xref py py-meth docutils literal notranslate">__delete__()</code>, it is a data descriptor; if it defines neither, it is a non-data descriptor. Normally, data descriptors define both <code class="xref py py-meth docutils literal notranslate">__get__()</code> and <code class="xref py py-meth docutils literal notranslate">__set__()</code>, while non-data descriptors have just the <code class="xref py py-meth docutils literal notranslate">__get__()</code> method. Data descriptors with <code class="xref py py-meth docutils literal notranslate">__get__()</code> and <code class="xref py py-meth docutils literal notranslate">__set__()</code> (and/or <code class="xref py py-meth docutils literal notranslate">__delete__()</code>) defined always override a redefinition in an instance dictionary. In contrast, non-data descriptors can be overridden by instances. Python methods (including those decorated with <a class="reference internal" href="../library/functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate">@staticmethod</code></a> and <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate">@classmethod</code></a>) are implemented as non-data descriptors. Accordingly, instances can redefine and override methods. This allows individual instances to acquire behaviors that differ from other instances of the same class. The <a class="reference internal" href="../library/functions.html#property" title="property"><code class="xref py py-func docutils literal notranslate">property()</code></a> function is implemented as a data descriptor. Accordingly, instances cannot override the behavior of a property. </section> <section id="slots"> <h4>3.3.2.4. __slots__<a class="headerlink" href="#slots" title="Link to this heading">¶</a></h4> __slots__ allow us to explicitly declare data members (like properties) and deny the creation of <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> and __weakref__ (unless explicitly declared in __slots__ or available in a parent.) The space saved over using <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> can be significant. Attribute lookup speed can be significantly improved as well. <dl class="py data"> <dt class="sig sig-object py" id="object.__slots__"> object.__slots__<a class="headerlink" href="#object.__slots__" title="Link to this definition">¶</a></dt> <dd>This class variable can be assigned a string, iterable, or sequence of strings with variable names used by instances. __slots__ reserves space for the declared variables and prevents the automatic creation of <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> and __weakref__ for each instance. </dd></dl> Notes on using __slots__: <ul class="simple"> <li>When inheriting from a class without __slots__, the <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> and __weakref__ attribute of the instances will always be accessible.</li> <li>Without a <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> variable, instances cannot be assigned new variables not listed in the __slots__ definition. Attempts to assign to an unlisted variable name raises <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. If dynamic assignment of new variables is desired, then add <code class="docutils literal notranslate">'__dict__'</code> to the sequence of strings in the __slots__ declaration.</li> <li>Without a __weakref__ variable for each instance, classes defining __slots__ do not support <a class="reference internal" href="../library/weakref.html#module-weakref" title="weakref: Support for weak references and weak dictionaries."><code class="xref py py-mod docutils literal notranslate">weak references</code></a> to its instances. If weak reference support is needed, then add <code class="docutils literal notranslate">'__weakref__'</code> to the sequence of strings in the __slots__ declaration.</li> <li>__slots__ are implemented at the class level by creating <a class="reference internal" href="#descriptors">descriptors</a> for each variable name. As a result, class attributes cannot be used to set default values for instance variables defined by __slots__; otherwise, the class attribute would overwrite the descriptor assignment.</li> <li>The action of a __slots__ declaration is not limited to the class where it is defined. __slots__ declared in parents are available in child classes. However, instances of a child subclass will get a <a class="reference internal" href="#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> and __weakref__ unless the subclass also defines __slots__ (which should only contain names of any additional slots).</li> <li>If a class defines a slot also defined in a base class, the instance variable defined by the base class slot is inaccessible (except by retrieving its descriptor directly from the base class). This renders the meaning of the program undefined. In the future, a check may be added to prevent this.</li> <li><a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> will be raised if nonempty __slots__ are defined for a class derived from a <a class="reference internal" href="../c-api/typeobj.html#c.PyTypeObject.tp_itemsize" title="PyTypeObject.tp_itemsize"><code class="xref c c-member docutils literal notranslate">"variable-length" built-in type</code></a> such as <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>, <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>, and <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>.</li> <li>Any non-string <a class="reference internal" href="../glossary.html#term-iterable">iterable</a> may be assigned to __slots__.</li> <li>If a <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dictionary</code></a> is used to assign __slots__, the dictionary keys will be used as the slot names. The values of the dictionary can be used to provide per-attribute docstrings that will be recognised by <a class="reference internal" href="../library/inspect.html#inspect.getdoc" title="inspect.getdoc"><code class="xref py py-func docutils literal notranslate">inspect.getdoc()</code></a> and displayed in the output of <a class="reference internal" href="../library/functions.html#help" title="help"><code class="xref py py-func docutils literal notranslate">help()</code></a>.</li> <li><a class="reference internal" href="#object.__class__" title="object.__class__"><code class="xref py py-attr docutils literal notranslate">__class__</code></a> assignment works only if both classes have the same __slots__.</li> <li><a class="reference internal" href="../tutorial/classes.html#tut-multiple">Multiple inheritance</a> with multiple slotted parent classes can be used, but only one parent is allowed to have attributes created by slots (the other bases must have empty slot layouts) - violations raise <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>.</li> <li>If an <a class="reference internal" href="../glossary.html#term-iterator">iterator</a> is used for __slots__ then a <a class="reference internal" href="../glossary.html#term-descriptor">descriptor</a> is created for each of the iterator’s values. However, the __slots__ attribute will be an empty iterator.</li> </ul> </section> </section> <section id="customizing-class-creation"> <h3>3.3.3. Customizing class creation<a class="headerlink" href="#customizing-class-creation" title="Link to this heading">¶</a></h3> Whenever a class inherits from another class, <a class="reference internal" href="#object.__init_subclass__" title="object.__init_subclass__"><code class="xref py py-meth docutils literal notranslate">__init_subclass__()</code></a> is called on the parent class. This way, it is possible to write classes which change the behavior of subclasses. This is closely related to class decorators, but where class decorators only affect the specific class they’re applied to, <code class="docutils literal notranslate">__init_subclass__</code> solely applies to future subclasses of the class defining the method. <dl class="py method"> <dt class="sig sig-object py" id="object.__init_subclass__"> classmethod object.__init_subclass__(cls)<a class="headerlink" href="#object.__init_subclass__" title="Link to this definition">¶</a></dt> <dd>This method is called whenever the containing class is subclassed. cls is then the new subclass. If defined as a normal instance method, this method is implicitly converted to a class method. Keyword arguments which are given to a new class are passed to the parent class’s <code class="docutils literal notranslate">__init_subclass__</code>. For compatibility with other classes using <code class="docutils literal notranslate">__init_subclass__</code>, one should take out the needed keyword arguments and pass the others over to the base class, as in: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Philosopher: def __init_subclass__(cls, /, default_name, **kwargs): super().__init_subclass__(**kwargs) cls.default_name = default_name class AustralianPhilosopher(Philosopher, default_name="Bruce"): pass </pre></div> </div> The default implementation <code class="docutils literal notranslate">object.__init_subclass__</code> does nothing, but raises an error if it is called with any arguments. <div class="admonition note"> Note The metaclass hint <code class="docutils literal notranslate">metaclass</code> is consumed by the rest of the type machinery, and is never passed to <code class="docutils literal notranslate">__init_subclass__</code> implementations. The actual metaclass (rather than the explicit hint) can be accessed as <code class="docutils literal notranslate">type(cls)</code>. </div> <div class="versionadded"> Added in version 3.6. </div> </dd></dl> When a class is created, <code class="xref py py-meth docutils literal notranslate">type.__new__()</code> scans the class variables and makes callbacks to those with a <a class="reference internal" href="#object.__set_name__" title="object.__set_name__"><code class="xref py py-meth docutils literal notranslate">__set_name__()</code></a> hook. <dl class="py method"> <dt class="sig sig-object py" id="object.__set_name__"> object.__set_name__(self, owner, name)<a class="headerlink" href="#object.__set_name__" title="Link to this definition">¶</a></dt> <dd>Automatically called at the time the owning class owner is created. The object has been assigned to name in that class: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class A: x = C() # Automatically calls: x.__set_name__(A, 'x') </pre></div> </div> If the class variable is assigned after the class is created, <a class="reference internal" href="#object.__set_name__" title="object.__set_name__"><code class="xref py py-meth docutils literal notranslate">__set_name__()</code></a> will not be called automatically. If needed, <a class="reference internal" href="#object.__set_name__" title="object.__set_name__"><code class="xref py py-meth docutils literal notranslate">__set_name__()</code></a> can be called directly: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class A: pass c = C() A.x = c # The hook is not called c.__set_name__(A, 'x') # Manually invoke the hook </pre></div> </div> See <a class="reference internal" href="#class-object-creation">Creating the class object</a> for more details. <div class="versionadded"> Added in version 3.6. </div> </dd></dl> <section id="metaclasses"> <h4>3.3.3.1. Metaclasses<a class="headerlink" href="#metaclasses" title="Link to this heading">¶</a></h4> By default, classes are constructed using <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-func docutils literal notranslate">type()</code></a>. The class body is executed in a new namespace and the class name is bound locally to the result of <code class="docutils literal notranslate">type(name, bases, namespace)</code>. The class creation process can be customized by passing the <code class="docutils literal notranslate">metaclass</code> keyword argument in the class definition line, or by inheriting from an existing class that included such an argument. In the following example, both <code class="docutils literal notranslate">MyClass</code> and <code class="docutils literal notranslate">MySubclass</code> are instances of <code class="docutils literal notranslate">Meta</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Meta(type): pass class MyClass(metaclass=Meta): pass class MySubclass(MyClass): pass </pre></div> </div> Any other keyword arguments that are specified in the class definition are passed through to all metaclass operations described below. When a class definition is executed, the following steps occur: <ul class="simple"> <li>MRO entries are resolved;</li> <li>the appropriate metaclass is determined;</li> <li>the class namespace is prepared;</li> <li>the class body is executed;</li> <li>the class object is created.</li> </ul> </section> <section id="resolving-mro-entries"> <h4>3.3.3.2. Resolving MRO entries<a class="headerlink" href="#resolving-mro-entries" title="Link to this heading">¶</a></h4> <dl class="py method"> <dt class="sig sig-object py" id="object.__mro_entries__"> object.__mro_entries__(self, bases)<a class="headerlink" href="#object.__mro_entries__" title="Link to this definition">¶</a></dt> <dd>If a base that appears in a class definition is not an instance of <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a>, then an <code class="xref py py-meth docutils literal notranslate">__mro_entries__()</code> method is searched on the base. If an <code class="xref py py-meth docutils literal notranslate">__mro_entries__()</code> method is found, the base is substituted with the result of a call to <code class="xref py py-meth docutils literal notranslate">__mro_entries__()</code> when creating the class. The method is called with the original bases tuple passed to the bases parameter, and must return a tuple of classes that will be used instead of the base. The returned tuple may be empty: in these cases, the original base is ignored. </dd></dl> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="reference internal" href="../library/types.html#types.resolve_bases" title="types.resolve_bases"><code class="xref py py-func docutils literal notranslate">types.resolve_bases()</code></a></dt><dd>Dynamically resolve bases that are not instances of <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a>. </dd> <dt><a class="reference internal" href="../library/types.html#types.get_original_bases" title="types.get_original_bases"><code class="xref py py-func docutils literal notranslate">types.get_original_bases()</code></a></dt><dd>Retrieve a class’s “original bases” prior to modifications by <a class="reference internal" href="#object.__mro_entries__" title="object.__mro_entries__"><code class="xref py py-meth docutils literal notranslate">__mro_entries__()</code></a>. </dd> <dt><a class="pep reference external" href="https://peps.python.org/pep-0560/">PEP 560</a></dt><dd>Core support for typing module and generic types. </dd> </dl> </div> </section> <section id="determining-the-appropriate-metaclass"> <h4>3.3.3.3. Determining the appropriate metaclass<a class="headerlink" href="#determining-the-appropriate-metaclass" title="Link to this heading">¶</a></h4> The appropriate metaclass for a class definition is determined as follows: <ul class="simple"> <li>if no bases and no explicit metaclass are given, then <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-func docutils literal notranslate">type()</code></a> is used;</li> <li>if an explicit metaclass is given and it is not an instance of <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-func docutils literal notranslate">type()</code></a>, then it is used directly as the metaclass;</li> <li>if an instance of <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-func docutils literal notranslate">type()</code></a> is given as the explicit metaclass, or bases are defined, then the most derived metaclass is used.</li> </ul> The most derived metaclass is selected from the explicitly specified metaclass (if any) and the metaclasses (i.e. <code class="docutils literal notranslate">type(cls)</code>) of all specified base classes. The most derived metaclass is one which is a subtype of all of these candidate metaclasses. If none of the candidate metaclasses meets that criterion, then the class definition will fail with <code class="docutils literal notranslate">TypeError</code>. </section> <section id="preparing-the-class-namespace"> <h4>3.3.3.4. Preparing the class namespace<a class="headerlink" href="#preparing-the-class-namespace" title="Link to this heading">¶</a></h4> Once the appropriate metaclass has been identified, then the class namespace is prepared. If the metaclass has a <code class="docutils literal notranslate">__prepare__</code> attribute, it is called as <code class="docutils literal notranslate">namespace = metaclass.__prepare__(name, bases, **kwds)</code> (where the additional keyword arguments, if any, come from the class definition). The <code class="docutils literal notranslate">__prepare__</code> method should be implemented as a <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate">classmethod</code></a>. The namespace returned by <code class="docutils literal notranslate">__prepare__</code> is passed in to <code class="docutils literal notranslate">__new__</code>, but when the final class object is created the namespace is copied into a new <code class="docutils literal notranslate">dict</code>. If the metaclass has no <code class="docutils literal notranslate">__prepare__</code> attribute, then the class namespace is initialised as an empty ordered mapping. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-3115/">PEP 3115</a> - Metaclasses in Python 3000</dt><dd>Introduced the <code class="docutils literal notranslate">__prepare__</code> namespace hook </dd> </dl> </div> </section> <section id="executing-the-class-body"> <h4>3.3.3.5. Executing the class body<a class="headerlink" href="#executing-the-class-body" title="Link to this heading">¶</a></h4> The class body is executed (approximately) as <code class="docutils literal notranslate">exec(body, globals(), namespace)</code>. The key difference from a normal call to <a class="reference internal" href="../library/functions.html#exec" title="exec"><code class="xref py py-func docutils literal notranslate">exec()</code></a> is that lexical scoping allows the class body (including any methods) to reference names from the current and outer scopes when the class definition occurs inside a function. However, even when the class definition occurs inside the function, methods defined inside the class still cannot see names defined at the class scope. Class variables must be accessed through the first parameter of instance or class methods, or through the implicit lexically scoped <code class="docutils literal notranslate">__class__</code> reference described in the next section. </section> <section id="creating-the-class-object"> <h4>3.3.3.6. Creating the class object<a class="headerlink" href="#creating-the-class-object" title="Link to this heading">¶</a></h4> Once the class namespace has been populated by executing the class body, the class object is created by calling <code class="docutils literal notranslate">metaclass(name, bases, namespace, **kwds)</code> (the additional keywords passed here are the same as those passed to <code class="docutils literal notranslate">__prepare__</code>). This class object is the one that will be referenced by the zero-argument form of <a class="reference internal" href="../library/functions.html#super" title="super"><code class="xref py py-func docutils literal notranslate">super()</code></a>. <code class="docutils literal notranslate">__class__</code> is an implicit closure reference created by the compiler if any methods in a class body refer to either <code class="docutils literal notranslate">__class__</code> or <code class="docutils literal notranslate">super</code>. This allows the zero argument form of <a class="reference internal" href="../library/functions.html#super" title="super"><code class="xref py py-func docutils literal notranslate">super()</code></a> to correctly identify the class being defined based on lexical scoping, while the class or instance that was used to make the current call is identified based on the first argument passed to the method. <div class="impl-detail compound"> CPython implementation detail: In CPython 3.6 and later, the <code class="docutils literal notranslate">__class__</code> cell is passed to the metaclass as a <code class="docutils literal notranslate">__classcell__</code> entry in the class namespace. If present, this must be propagated up to the <code class="docutils literal notranslate">type.__new__</code> call in order for the class to be initialised correctly. Failing to do so will result in a <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> in Python 3.8. </div> When using the default metaclass <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a>, or any metaclass that ultimately calls <code class="docutils literal notranslate">type.__new__</code>, the following additional customization steps are invoked after creating the class object: <ol class="arabic simple"> <li>The <code class="docutils literal notranslate">type.__new__</code> method collects all of the attributes in the class namespace that define a <a class="reference internal" href="#object.__set_name__" title="object.__set_name__"><code class="xref py py-meth docutils literal notranslate">__set_name__()</code></a> method;</li> <li>Those <code class="docutils literal notranslate">__set_name__</code> methods are called with the class being defined and the assigned name of that particular attribute;</li> <li>The <a class="reference internal" href="#object.__init_subclass__" title="object.__init_subclass__"><code class="xref py py-meth docutils literal notranslate">__init_subclass__()</code></a> hook is called on the immediate parent of the new class in its method resolution order.</li> </ol> After the class object is created, it is passed to the class decorators included in the class definition (if any) and the resulting object is bound in the local namespace as the defined class. When a new class is created by <code class="docutils literal notranslate">type.__new__</code>, the object provided as the namespace parameter is copied to a new ordered mapping and the original object is discarded. The new copy is wrapped in a read-only proxy, which becomes the <a class="reference internal" href="#type.__dict__" title="type.__dict__"><code class="xref py py-attr docutils literal notranslate">__dict__</code></a> attribute of the class object. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-3135/">PEP 3135</a> - New super</dt><dd>Describes the implicit <code class="docutils literal notranslate">__class__</code> closure reference </dd> </dl> </div> </section> <section id="uses-for-metaclasses"> <h4>3.3.3.7. Uses for metaclasses<a class="headerlink" href="#uses-for-metaclasses" title="Link to this heading">¶</a></h4> The potential uses for metaclasses are boundless. Some ideas that have been explored include enum, logging, interface checking, automatic delegation, automatic property creation, proxies, frameworks, and automatic resource locking/synchronization. </section> </section> <section id="customizing-instance-and-subclass-checks"> <h3>3.3.4. Customizing instance and subclass checks<a class="headerlink" href="#customizing-instance-and-subclass-checks" title="Link to this heading">¶</a></h3> The following methods are used to override the default behavior of the <a class="reference internal" href="../library/functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> and <a class="reference internal" href="../library/functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate">issubclass()</code></a> built-in functions. In particular, the metaclass <a class="reference internal" href="../library/abc.html#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate">abc.ABCMeta</code></a> implements these methods in order to allow the addition of Abstract Base Classes (ABCs) as “virtual base classes” to any class or type (including built-in types), including other ABCs. <dl class="py method"> <dt class="sig sig-object py" id="type.__instancecheck__"> type.__instancecheck__(self, instance)<a class="headerlink" href="#type.__instancecheck__" title="Link to this definition">¶</a></dt> <dd>Return true if instance should be considered a (direct or indirect) instance of class. If defined, called to implement <code class="docutils literal notranslate">isinstance(instance, class)</code>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="type.__subclasscheck__"> type.__subclasscheck__(self, subclass)<a class="headerlink" href="#type.__subclasscheck__" title="Link to this definition">¶</a></dt> <dd>Return true if subclass should be considered a (direct or indirect) subclass of class. If defined, called to implement <code class="docutils literal notranslate">issubclass(subclass, class)</code>. </dd></dl> Note that these methods are looked up on the type (metaclass) of a class. They cannot be defined as class methods in the actual class. This is consistent with the lookup of special methods that are called on instances, only in this case the instance is itself a class. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-3119/">PEP 3119</a> - Introducing Abstract Base Classes</dt><dd>Includes the specification for customizing <a class="reference internal" href="../library/functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> and <a class="reference internal" href="../library/functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate">issubclass()</code></a> behavior through <a class="reference internal" href="#type.__instancecheck__" title="type.__instancecheck__"><code class="xref py py-meth docutils literal notranslate">__instancecheck__()</code></a> and <a class="reference internal" href="#type.__subclasscheck__" title="type.__subclasscheck__"><code class="xref py py-meth docutils literal notranslate">__subclasscheck__()</code></a>, with motivation for this functionality in the context of adding Abstract Base Classes (see the <a class="reference internal" href="../library/abc.html#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate">abc</code></a> module) to the language. </dd> </dl> </div> </section> <section id="emulating-generic-types"> <h3>3.3.5. Emulating generic types<a class="headerlink" href="#emulating-generic-types" title="Link to this heading">¶</a></h3> When using <a class="reference internal" href="../glossary.html#term-annotation">type annotations</a>, it is often useful to parameterize a <a class="reference internal" href="../glossary.html#term-generic-type">generic type</a> using Python’s square-brackets notation. For example, the annotation <code class="docutils literal notranslate">list[int]</code> might be used to signify a <a class="reference internal" href="../library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a> in which all the elements are of type <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> - Type Hints</dt><dd>Introducing Python’s framework for type annotations </dd> <dt><a class="reference internal" href="../library/stdtypes.html#types-genericalias">Generic Alias Types</a></dt><dd>Documentation for objects representing parameterized generic classes </dd> <dt><a class="reference internal" href="../library/typing.html#generics">Generics</a>, <a class="reference internal" href="../library/typing.html#user-defined-generics">user-defined generics</a> and <a class="reference internal" href="../library/typing.html#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">typing.Generic</code></a></dt><dd>Documentation on how to implement generic classes that can be parameterized at runtime and understood by static type-checkers. </dd> </dl> </div> A class can generally only be parameterized if it defines the special class method <code class="docutils literal notranslate">__class_getitem__()</code>. <dl class="py method"> <dt class="sig sig-object py" id="object.__class_getitem__"> classmethod object.__class_getitem__(cls, key)<a class="headerlink" href="#object.__class_getitem__" title="Link to this definition">¶</a></dt> <dd>Return an object representing the specialization of a generic class by type arguments found in key. When defined on a class, <code class="docutils literal notranslate">__class_getitem__()</code> is automatically a class method. As such, there is no need for it to be decorated with <a class="reference internal" href="../library/functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate">@classmethod</code></a> when it is defined. </dd></dl> <section id="the-purpose-of-class-getitem"> <h4>3.3.5.1. The purpose of __class_getitem__<a class="headerlink" href="#the-purpose-of-class-getitem" title="Link to this heading">¶</a></h4> The purpose of <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> is to allow runtime parameterization of standard-library generic classes in order to more easily apply <a class="reference internal" href="../glossary.html#term-type-hint">type hints</a> to these classes. To implement custom generic classes that can be parameterized at runtime and understood by static type-checkers, users should either inherit from a standard library class that already implements <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a>, or inherit from <a class="reference internal" href="../library/typing.html#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">typing.Generic</code></a>, which has its own implementation of <code class="docutils literal notranslate">__class_getitem__()</code>. Custom implementations of <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> on classes defined outside of the standard library may not be understood by third-party type-checkers such as mypy. Using <code class="docutils literal notranslate">__class_getitem__()</code> on any class for purposes other than type hinting is discouraged. </section> <section id="class-getitem-versus-getitem"> <h4>3.3.5.2. __class_getitem__ versus __getitem__<a class="headerlink" href="#class-getitem-versus-getitem" title="Link to this heading">¶</a></h4> Usually, the <a class="reference internal" href="expressions.html#subscriptions">subscription</a> of an object using square brackets will call the <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> instance method defined on the object’s class. However, if the object being subscribed is itself a class, the class method <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> may be called instead. <code class="docutils literal notranslate">__class_getitem__()</code> should return a <a class="reference internal" href="../library/stdtypes.html#types-genericalias">GenericAlias</a> object if it is properly defined. Presented with the <a class="reference internal" href="../glossary.html#term-expression">expression</a> <code class="docutils literal notranslate">obj[x]</code>, the Python interpreter follows something like the following process to decide whether <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> or <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> should be called: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from inspect import isclass def subscribe(obj, x): """Return the result of the expression 'obj[x]'""" class_of_obj = type(obj) # If the class of obj defines __getitem__, # call class_of_obj.__getitem__(obj, x) if hasattr(class_of_obj, '__getitem__'): return class_of_obj.__getitem__(obj, x) # Else, if obj is a class and defines __class_getitem__, # call obj.__class_getitem__(x) elif isclass(obj) and hasattr(obj, '__class_getitem__'): return obj.__class_getitem__(x) # Else, raise an exception else: raise TypeError( f"'{class_of_obj.__name__}' object is not subscriptable" ) </pre></div> </div> In Python, all classes are themselves instances of other classes. The class of a class is known as that class’s <a class="reference internal" href="../glossary.html#term-metaclass">metaclass</a>, and most classes have the <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a> class as their metaclass. <a class="reference internal" href="../library/functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a> does not define <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>, meaning that expressions such as <code class="docutils literal notranslate">list[int]</code>, <code class="docutils literal notranslate">dict[str, float]</code> and <code class="docutils literal notranslate">tuple[str, bytes]</code> all result in <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> being called: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> # list has class "type" as its metaclass, like most classes: >>> type(list) <class 'type'> >>> type(dict) == type(list) == type(tuple) == type(str) == type(bytes) True >>> # "list[int]" calls "list.__class_getitem__(int)" >>> list[int] list[int] >>> # list.__class_getitem__ returns a GenericAlias object: >>> type(list[int]) <class 'types.GenericAlias'> </pre></div> </div> However, if a class has a custom metaclass that defines <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>, subscribing the class may result in different behaviour. An example of this can be found in the <a class="reference internal" href="../library/enum.html#module-enum" title="enum: Implementation of an enumeration class."><code class="xref py py-mod docutils literal notranslate">enum</code></a> module: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> from enum import Enum >>> class Menu(Enum): ... """A breakfast menu""" ... SPAM = 'spam' ... BACON = 'bacon' ... >>> # Enum classes have a custom metaclass: >>> type(Menu) <class 'enum.EnumMeta'> >>> # EnumMeta defines __getitem__, >>> # so __class_getitem__ is not called, >>> # and the result is not a GenericAlias object: >>> Menu['SPAM'] <Menu.SPAM: 'spam'> >>> type(Menu['SPAM']) <enum 'Menu'> </pre></div> </div> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0560/">PEP 560</a> - Core Support for typing module and generic types</dt><dd>Introducing <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a>, and outlining when a <a class="reference internal" href="expressions.html#subscriptions">subscription</a> results in <code class="docutils literal notranslate">__class_getitem__()</code> being called instead of <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> </dd> </dl> </div> </section> </section> <section id="emulating-callable-objects"> <h3>3.3.6. Emulating callable objects<a class="headerlink" href="#emulating-callable-objects" title="Link to this heading">¶</a></h3> <dl class="py method"> <dt class="sig sig-object py" id="object.__call__"> object.__call__(self[, args...])<a class="headerlink" href="#object.__call__" title="Link to this definition">¶</a></dt> <dd>Called when the instance is “called” as a function; if this method is defined, <code class="docutils literal notranslate">x(arg1, arg2, ...)</code> roughly translates to <code class="docutils literal notranslate">type(x).__call__(x, arg1, ...)</code>. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not provide this method. </dd></dl> </section> <section id="emulating-container-types"> <h3>3.3.7. Emulating container types<a class="headerlink" href="#emulating-container-types" title="Link to this heading">¶</a></h3> The following methods can be defined to implement container objects. None of them are provided by the <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself. Containers usually are <a class="reference internal" href="../glossary.html#term-sequence">sequences</a> (such as <a class="reference internal" href="../library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">lists</code></a> or <a class="reference internal" href="../library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuples</code></a>) or <a class="reference internal" href="../glossary.html#term-mapping">mappings</a> (like <a class="reference internal" href="../glossary.html#term-dictionary">dictionaries</a>), but can represent other containers as well. The first set of methods is used either to emulate a sequence or to emulate a mapping; the difference is that for a sequence, the allowable keys should be the integers k for which <code class="docutils literal notranslate">0 <= k < N</code> where N is the length of the sequence, or <a class="reference internal" href="../library/functions.html#slice" title="slice"><code class="xref py py-class docutils literal notranslate">slice</code></a> objects, which define a range of items. It is also recommended that mappings provide the methods <code class="xref py py-meth docutils literal notranslate">keys()</code>, <code class="xref py py-meth docutils literal notranslate">values()</code>, <code class="xref py py-meth docutils literal notranslate">items()</code>, <code class="xref py py-meth docutils literal notranslate">get()</code>, <code class="xref py py-meth docutils literal notranslate">clear()</code>, <code class="xref py py-meth docutils literal notranslate">setdefault()</code>, <code class="xref py py-meth docutils literal notranslate">pop()</code>, <code class="xref py py-meth docutils literal notranslate">popitem()</code>, <code class="xref py py-meth docutils literal notranslate">copy()</code>, and <code class="xref py py-meth docutils literal notranslate">update()</code> behaving similar to those for Python’s standard <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dictionary</code></a> objects. The <a class="reference internal" href="../library/collections.abc.html#module-collections.abc" title="collections.abc: Abstract base classes for containers"><code class="xref py py-mod docutils literal notranslate">collections.abc</code></a> module provides a <a class="reference internal" href="../library/collections.abc.html#collections.abc.MutableMapping" title="collections.abc.MutableMapping"><code class="xref py py-class docutils literal notranslate">MutableMapping</code></a> <a class="reference internal" href="../glossary.html#term-abstract-base-class">abstract base class</a> to help create those methods from a base set of <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>, <a class="reference internal" href="#object.__setitem__" title="object.__setitem__"><code class="xref py py-meth docutils literal notranslate">__setitem__()</code></a>, <a class="reference internal" href="#object.__delitem__" title="object.__delitem__"><code class="xref py py-meth docutils literal notranslate">__delitem__()</code></a>, and <code class="xref py py-meth docutils literal notranslate">keys()</code>. Mutable sequences should provide methods <code class="xref py py-meth docutils literal notranslate">append()</code>, <code class="xref py py-meth docutils literal notranslate">count()</code>, <code class="xref py py-meth docutils literal notranslate">index()</code>, <code class="xref py py-meth docutils literal notranslate">extend()</code>, <code class="xref py py-meth docutils literal notranslate">insert()</code>, <code class="xref py py-meth docutils literal notranslate">pop()</code>, <code class="xref py py-meth docutils literal notranslate">remove()</code>, <code class="xref py py-meth docutils literal notranslate">reverse()</code> and <code class="xref py py-meth docutils literal notranslate">sort()</code>, like Python standard <a class="reference internal" href="../library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a> objects. Finally, sequence types should implement addition (meaning concatenation) and multiplication (meaning repetition) by defining the methods <a class="reference internal" href="#object.__add__" title="object.__add__"><code class="xref py py-meth docutils literal notranslate">__add__()</code></a>, <a class="reference internal" href="#object.__radd__" title="object.__radd__"><code class="xref py py-meth docutils literal notranslate">__radd__()</code></a>, <a class="reference internal" href="#object.__iadd__" title="object.__iadd__"><code class="xref py py-meth docutils literal notranslate">__iadd__()</code></a>, <a class="reference internal" href="#object.__mul__" title="object.__mul__"><code class="xref py py-meth docutils literal notranslate">__mul__()</code></a>, <a class="reference internal" href="#object.__rmul__" title="object.__rmul__"><code class="xref py py-meth docutils literal notranslate">__rmul__()</code></a> and <a class="reference internal" href="#object.__imul__" title="object.__imul__"><code class="xref py py-meth docutils literal notranslate">__imul__()</code></a> described below; they should not define other numerical operators. It is recommended that both mappings and sequences implement the <a class="reference internal" href="#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate">__contains__()</code></a> method to allow efficient use of the <code class="docutils literal notranslate">in</code> operator; for mappings, <code class="docutils literal notranslate">in</code> should search the mapping’s keys; for sequences, it should search through the values. It is further recommended that both mappings and sequences implement the <a class="reference internal" href="#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a> method to allow efficient iteration through the container; for mappings, <code class="xref py py-meth docutils literal notranslate">__iter__()</code> should iterate through the object’s keys; for sequences, it should iterate through the values. <dl class="py method"> <dt class="sig sig-object py" id="object.__len__"> object.__len__(self)<a class="headerlink" href="#object.__len__" title="Link to this definition">¶</a></dt> <dd>Called to implement the built-in function <a class="reference internal" href="../library/functions.html#len" title="len"><code class="xref py py-func docutils literal notranslate">len()</code></a>. Should return the length of the object, an integer <code class="docutils literal notranslate">>=</code> 0. Also, an object that doesn’t define a <a class="reference internal" href="#object.__bool__" title="object.__bool__"><code class="xref py py-meth docutils literal notranslate">__bool__()</code></a> method and whose <code class="xref py py-meth docutils literal notranslate">__len__()</code> method returns zero is considered to be false in a Boolean context. <div class="impl-detail compound"> CPython implementation detail: In CPython, the length is required to be at most <a class="reference internal" href="../library/sys.html#sys.maxsize" title="sys.maxsize"><code class="xref py py-data docutils literal notranslate">sys.maxsize</code></a>. If the length is larger than <code class="xref py py-data docutils literal notranslate">sys.maxsize</code> some features (such as <a class="reference internal" href="../library/functions.html#len" title="len"><code class="xref py py-func docutils literal notranslate">len()</code></a>) may raise <a class="reference internal" href="../library/exceptions.html#OverflowError" title="OverflowError"><code class="xref py py-exc docutils literal notranslate">OverflowError</code></a>. To prevent raising <code class="xref py py-exc docutils literal notranslate">OverflowError</code> by truth value testing, an object must define a <a class="reference internal" href="#object.__bool__" title="object.__bool__"><code class="xref py py-meth docutils literal notranslate">__bool__()</code></a> method. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__length_hint__"> object.__length_hint__(self)<a class="headerlink" href="#object.__length_hint__" title="Link to this definition">¶</a></dt> <dd>Called to implement <a class="reference internal" href="../library/operator.html#operator.length_hint" title="operator.length_hint"><code class="xref py py-func docutils literal notranslate">operator.length_hint()</code></a>. Should return an estimated length for the object (which may be greater or less than the actual length). The length must be an integer <code class="docutils literal notranslate">>=</code> 0. The return value may also be <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>, which is treated the same as if the <code class="docutils literal notranslate">__length_hint__</code> method didn’t exist at all. This method is purely an optimization and is never required for correctness. <div class="versionadded"> Added in version 3.4. </div> </dd></dl> <div class="admonition note" id="index-101"> Note Slicing is done exclusively with the following three methods. A call like <div class="highlight-python3 notranslate"><div class="highlight"><pre>a[1:2] = b </pre></div> </div> is translated to <div class="highlight-python3 notranslate"><div class="highlight"><pre>a[slice(1, 2, None)] = b </pre></div> </div> and so forth. Missing slice items are always filled in with <code class="docutils literal notranslate">None</code>. </div> <dl class="py method"> <dt class="sig sig-object py" id="object.__getitem__"> object.__getitem__(self, key)<a class="headerlink" href="#object.__getitem__" title="Link to this definition">¶</a></dt> <dd>Called to implement evaluation of <code class="docutils literal notranslate">self[key]</code>. For <a class="reference internal" href="../glossary.html#term-sequence">sequence</a> types, the accepted keys should be integers. Optionally, they may support <a class="reference internal" href="../library/functions.html#slice" title="slice"><code class="xref py py-class docutils literal notranslate">slice</code></a> objects as well. Negative index support is also optional. If key is of an inappropriate type, <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> may be raised; if key is a value outside the set of indexes for the sequence (after any special interpretation of negative values), <a class="reference internal" href="../library/exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate">IndexError</code></a> should be raised. For <a class="reference internal" href="../glossary.html#term-mapping">mapping</a> types, if key is missing (not in the container), <a class="reference internal" href="../library/exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate">KeyError</code></a> should be raised. <div class="admonition note"> Note <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate">for</code></a> loops expect that an <a class="reference internal" href="../library/exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate">IndexError</code></a> will be raised for illegal indexes to allow proper detection of the end of the sequence. </div> <div class="admonition note"> Note When <a class="reference internal" href="expressions.html#subscriptions">subscripting</a> a class, the special class method <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> may be called instead of <code class="docutils literal notranslate">__getitem__()</code>. See <a class="reference internal" href="#classgetitem-versus-getitem">__class_getitem__ versus __getitem__</a> for more details. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__setitem__"> object.__setitem__(self, key, value)<a class="headerlink" href="#object.__setitem__" title="Link to this definition">¶</a></dt> <dd>Called to implement assignment to <code class="docutils literal notranslate">self[key]</code>. Same note as for <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>. This should only be implemented for mappings if the objects support changes to the values for keys, or if new keys can be added, or for sequences if elements can be replaced. The same exceptions should be raised for improper key values as for the <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> method. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__delitem__"> object.__delitem__(self, key)<a class="headerlink" href="#object.__delitem__" title="Link to this definition">¶</a></dt> <dd>Called to implement deletion of <code class="docutils literal notranslate">self[key]</code>. Same note as for <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>. This should only be implemented for mappings if the objects support removal of keys, or for sequences if elements can be removed from the sequence. The same exceptions should be raised for improper key values as for the <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> method. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__missing__"> object.__missing__(self, key)<a class="headerlink" href="#object.__missing__" title="Link to this definition">¶</a></dt> <dd>Called by <a class="reference internal" href="../library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>.<a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> to implement <code class="docutils literal notranslate">self[key]</code> for dict subclasses when key is not in the dictionary. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__iter__"> object.__iter__(self)<a class="headerlink" href="#object.__iter__" title="Link to this definition">¶</a></dt> <dd>This method is called when an <a class="reference internal" href="../glossary.html#term-iterator">iterator</a> is required for a container. This method should return a new iterator object that can iterate over all the objects in the container. For mappings, it should iterate over the keys of the container. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__reversed__"> object.__reversed__(self)<a class="headerlink" href="#object.__reversed__" title="Link to this definition">¶</a></dt> <dd>Called (if present) by the <a class="reference internal" href="../library/functions.html#reversed" title="reversed"><code class="xref py py-func docutils literal notranslate">reversed()</code></a> built-in to implement reverse iteration. It should return a new iterator object that iterates over all the objects in the container in reverse order. If the <a class="reference internal" href="#object.__reversed__" title="object.__reversed__"><code class="xref py py-meth docutils literal notranslate">__reversed__()</code></a> method is not provided, the <a class="reference internal" href="../library/functions.html#reversed" title="reversed"><code class="xref py py-func docutils literal notranslate">reversed()</code></a> built-in will fall back to using the sequence protocol (<a class="reference internal" href="#object.__len__" title="object.__len__"><code class="xref py py-meth docutils literal notranslate">__len__()</code></a> and <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>). Objects that support the sequence protocol should only provide <a class="reference internal" href="#object.__reversed__" title="object.__reversed__"><code class="xref py py-meth docutils literal notranslate">__reversed__()</code></a> if they can provide an implementation that is more efficient than the one provided by <a class="reference internal" href="../library/functions.html#reversed" title="reversed"><code class="xref py py-func docutils literal notranslate">reversed()</code></a>. </dd></dl> The membership test operators (<a class="reference internal" href="expressions.html#in"><code class="xref std std-keyword docutils literal notranslate">in</code></a> and <a class="reference internal" href="expressions.html#not-in"><code class="xref std std-keyword docutils literal notranslate">not in</code></a>) are normally implemented as an iteration through a container. However, container objects can supply the following special method with a more efficient implementation, which also does not require the object be iterable. <dl class="py method"> <dt class="sig sig-object py" id="object.__contains__"> object.__contains__(self, item)<a class="headerlink" href="#object.__contains__" title="Link to this definition">¶</a></dt> <dd>Called to implement membership test operators. Should return true if item is in self, false otherwise. For mapping objects, this should consider the keys of the mapping rather than the values or the key-item pairs. For objects that don’t define <a class="reference internal" href="#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate">__contains__()</code></a>, the membership test first tries iteration via <a class="reference internal" href="#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a>, then the old sequence iteration protocol via <a class="reference internal" href="#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>, see <a class="reference internal" href="expressions.html#membership-test-details">this section in the language reference</a>. </dd></dl> </section> <section id="emulating-numeric-types"> <h3>3.3.8. Emulating numeric types<a class="headerlink" href="#emulating-numeric-types" title="Link to this heading">¶</a></h3> The following methods can be defined to emulate numeric objects. Methods corresponding to operations that are not supported by the particular kind of number implemented (e.g., bitwise operations for non-integral numbers) should be left undefined. <dl class="py method"> <dt class="sig sig-object py" id="object.__add__"> object.__add__(self, other)<a class="headerlink" href="#object.__add__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__sub__"> object.__sub__(self, other)<a class="headerlink" href="#object.__sub__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__mul__"> object.__mul__(self, other)<a class="headerlink" href="#object.__mul__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__matmul__"> object.__matmul__(self, other)<a class="headerlink" href="#object.__matmul__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__truediv__"> object.__truediv__(self, other)<a class="headerlink" href="#object.__truediv__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__floordiv__"> object.__floordiv__(self, other)<a class="headerlink" href="#object.__floordiv__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__mod__"> object.__mod__(self, other)<a class="headerlink" href="#object.__mod__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__divmod__"> object.__divmod__(self, other)<a class="headerlink" href="#object.__divmod__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__pow__"> object.__pow__(self, other[, modulo])<a class="headerlink" href="#object.__pow__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__lshift__"> object.__lshift__(self, other)<a class="headerlink" href="#object.__lshift__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rshift__"> object.__rshift__(self, other)<a class="headerlink" href="#object.__rshift__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__and__"> object.__and__(self, other)<a class="headerlink" href="#object.__and__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__xor__"> object.__xor__(self, other)<a class="headerlink" href="#object.__xor__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__or__"> object.__or__(self, other)<a class="headerlink" href="#object.__or__" title="Link to this definition">¶</a></dt> <dd>These methods are called to implement the binary arithmetic operations (<code class="docutils literal notranslate">+</code>, <code class="docutils literal notranslate">-</code>, <code class="docutils literal notranslate">*</code>, <code class="docutils literal notranslate">@</code>, <code class="docutils literal notranslate">/</code>, <code class="docutils literal notranslate">//</code>, <code class="docutils literal notranslate">%</code>, <a class="reference internal" href="../library/functions.html#divmod" title="divmod"><code class="xref py py-func docutils literal notranslate">divmod()</code></a>, <a class="reference internal" href="../library/functions.html#pow" title="pow"><code class="xref py py-func docutils literal notranslate">pow()</code></a>, <code class="docutils literal notranslate">**</code>, <code class="docutils literal notranslate"><<</code>, <code class="docutils literal notranslate">>></code>, <code class="docutils literal notranslate">&</code>, <code class="docutils literal notranslate">^</code>, <code class="docutils literal notranslate">|</code>). For instance, to evaluate the expression <code class="docutils literal notranslate">x + y</code>, where x is an instance of a class that has an <a class="reference internal" href="#object.__add__" title="object.__add__"><code class="xref py py-meth docutils literal notranslate">__add__()</code></a> method, <code class="docutils literal notranslate">type(x).__add__(x, y)</code> is called. The <a class="reference internal" href="#object.__divmod__" title="object.__divmod__"><code class="xref py py-meth docutils literal notranslate">__divmod__()</code></a> method should be the equivalent to using <a class="reference internal" href="#object.__floordiv__" title="object.__floordiv__"><code class="xref py py-meth docutils literal notranslate">__floordiv__()</code></a> and <a class="reference internal" href="#object.__mod__" title="object.__mod__"><code class="xref py py-meth docutils literal notranslate">__mod__()</code></a>; it should not be related to <a class="reference internal" href="#object.__truediv__" title="object.__truediv__"><code class="xref py py-meth docutils literal notranslate">__truediv__()</code></a>. Note that <a class="reference internal" href="#object.__pow__" title="object.__pow__"><code class="xref py py-meth docutils literal notranslate">__pow__()</code></a> should be defined to accept an optional third argument if the ternary version of the built-in <a class="reference internal" href="../library/functions.html#pow" title="pow"><code class="xref py py-func docutils literal notranslate">pow()</code></a> function is to be supported. If one of those methods does not support the operation with the supplied arguments, it should return <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__radd__"> object.__radd__(self, other)<a class="headerlink" href="#object.__radd__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rsub__"> object.__rsub__(self, other)<a class="headerlink" href="#object.__rsub__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rmul__"> object.__rmul__(self, other)<a class="headerlink" href="#object.__rmul__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rmatmul__"> object.__rmatmul__(self, other)<a class="headerlink" href="#object.__rmatmul__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rtruediv__"> object.__rtruediv__(self, other)<a class="headerlink" href="#object.__rtruediv__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rfloordiv__"> object.__rfloordiv__(self, other)<a class="headerlink" href="#object.__rfloordiv__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rmod__"> object.__rmod__(self, other)<a class="headerlink" href="#object.__rmod__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rdivmod__"> object.__rdivmod__(self, other)<a class="headerlink" href="#object.__rdivmod__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rpow__"> object.__rpow__(self, other[, modulo])<a class="headerlink" href="#object.__rpow__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rlshift__"> object.__rlshift__(self, other)<a class="headerlink" href="#object.__rlshift__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rrshift__"> object.__rrshift__(self, other)<a class="headerlink" href="#object.__rrshift__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rand__"> object.__rand__(self, other)<a class="headerlink" href="#object.__rand__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__rxor__"> object.__rxor__(self, other)<a class="headerlink" href="#object.__rxor__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ror__"> object.__ror__(self, other)<a class="headerlink" href="#object.__ror__" title="Link to this definition">¶</a></dt> <dd>These methods are called to implement the binary arithmetic operations (<code class="docutils literal notranslate">+</code>, <code class="docutils literal notranslate">-</code>, <code class="docutils literal notranslate">*</code>, <code class="docutils literal notranslate">@</code>, <code class="docutils literal notranslate">/</code>, <code class="docutils literal notranslate">//</code>, <code class="docutils literal notranslate">%</code>, <a class="reference internal" href="../library/functions.html#divmod" title="divmod"><code class="xref py py-func docutils literal notranslate">divmod()</code></a>, <a class="reference internal" href="../library/functions.html#pow" title="pow"><code class="xref py py-func docutils literal notranslate">pow()</code></a>, <code class="docutils literal notranslate">**</code>, <code class="docutils literal notranslate"><<</code>, <code class="docutils literal notranslate">>></code>, <code class="docutils literal notranslate">&</code>, <code class="docutils literal notranslate">^</code>, <code class="docutils literal notranslate">|</code>) with reflected (swapped) operands. These functions are only called if the left operand does not support the corresponding operation <a class="footnote-reference brackets" href="#id21" id="id16" role="doc-noteref">[3]</a> and the operands are of different types. <a class="footnote-reference brackets" href="#id22" id="id17" role="doc-noteref">[4]</a> For instance, to evaluate the expression <code class="docutils literal notranslate">x - y</code>, where y is an instance of a class that has an <a class="reference internal" href="#object.__rsub__" title="object.__rsub__"><code class="xref py py-meth docutils literal notranslate">__rsub__()</code></a> method, <code class="docutils literal notranslate">type(y).__rsub__(y, x)</code> is called if <code class="docutils literal notranslate">type(x).__sub__(x, y)</code> returns <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>. Note that ternary <a class="reference internal" href="../library/functions.html#pow" title="pow"><code class="xref py py-func docutils literal notranslate">pow()</code></a> will not try calling <a class="reference internal" href="#object.__rpow__" title="object.__rpow__"><code class="xref py py-meth docutils literal notranslate">__rpow__()</code></a> (the coercion rules would become too complicated). <div class="admonition note"> Note If the right operand’s type is a subclass of the left operand’s type and that subclass provides a different implementation of the reflected method for the operation, this method will be called before the left operand’s non-reflected method. This behavior allows subclasses to override their ancestors’ operations. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__iadd__"> object.__iadd__(self, other)<a class="headerlink" href="#object.__iadd__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__isub__"> object.__isub__(self, other)<a class="headerlink" href="#object.__isub__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__imul__"> object.__imul__(self, other)<a class="headerlink" href="#object.__imul__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__imatmul__"> object.__imatmul__(self, other)<a class="headerlink" href="#object.__imatmul__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__itruediv__"> object.__itruediv__(self, other)<a class="headerlink" href="#object.__itruediv__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ifloordiv__"> object.__ifloordiv__(self, other)<a class="headerlink" href="#object.__ifloordiv__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__imod__"> object.__imod__(self, other)<a class="headerlink" href="#object.__imod__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ipow__"> object.__ipow__(self, other[, modulo])<a class="headerlink" href="#object.__ipow__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ilshift__"> object.__ilshift__(self, other)<a class="headerlink" href="#object.__ilshift__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__irshift__"> object.__irshift__(self, other)<a class="headerlink" href="#object.__irshift__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__iand__"> object.__iand__(self, other)<a class="headerlink" href="#object.__iand__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ixor__"> object.__ixor__(self, other)<a class="headerlink" href="#object.__ixor__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ior__"> object.__ior__(self, other)<a class="headerlink" href="#object.__ior__" title="Link to this definition">¶</a></dt> <dd>These methods are called to implement the augmented arithmetic assignments (<code class="docutils literal notranslate">+=</code>, <code class="docutils literal notranslate">-=</code>, <code class="docutils literal notranslate">*=</code>, <code class="docutils literal notranslate">@=</code>, <code class="docutils literal notranslate">/=</code>, <code class="docutils literal notranslate">//=</code>, <code class="docutils literal notranslate">%=</code>, <code class="docutils literal notranslate">**=</code>, <code class="docutils literal notranslate"><<=</code>, <code class="docutils literal notranslate">>>=</code>, <code class="docutils literal notranslate">&=</code>, <code class="docutils literal notranslate">^=</code>, <code class="docutils literal notranslate">|=</code>). These methods should attempt to do the operation in-place (modifying self) and return the result (which could be, but does not have to be, self). If a specific method is not defined, or if that method returns <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>, the augmented assignment falls back to the normal methods. For instance, if x is an instance of a class with an <a class="reference internal" href="#object.__iadd__" title="object.__iadd__"><code class="xref py py-meth docutils literal notranslate">__iadd__()</code></a> method, <code class="docutils literal notranslate">x += y</code> is equivalent to <code class="docutils literal notranslate">x = x.__iadd__(y)</code> . If <a class="reference internal" href="#object.__iadd__" title="object.__iadd__"><code class="xref py py-meth docutils literal notranslate">__iadd__()</code></a> does not exist, or if <code class="docutils literal notranslate">x.__iadd__(y)</code> returns <code class="xref py py-data docutils literal notranslate">NotImplemented</code>, <code class="docutils literal notranslate">x.__add__(y)</code> and <code class="docutils literal notranslate">y.__radd__(x)</code> are considered, as with the evaluation of <code class="docutils literal notranslate">x + y</code>. In certain situations, augmented assignment can result in unexpected errors (see <a class="reference internal" href="../faq/programming.html#faq-augmented-assignment-tuple-error">Why does a_tuple[i] += [‘item’] raise an exception when the addition works?</a>), but this behavior is in fact part of the data model. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__neg__"> object.__neg__(self)<a class="headerlink" href="#object.__neg__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__pos__"> object.__pos__(self)<a class="headerlink" href="#object.__pos__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__abs__"> object.__abs__(self)<a class="headerlink" href="#object.__abs__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__invert__"> object.__invert__(self)<a class="headerlink" href="#object.__invert__" title="Link to this definition">¶</a></dt> <dd>Called to implement the unary arithmetic operations (<code class="docutils literal notranslate">-</code>, <code class="docutils literal notranslate">+</code>, <a class="reference internal" href="../library/functions.html#abs" title="abs"><code class="xref py py-func docutils literal notranslate">abs()</code></a> and <code class="docutils literal notranslate">~</code>). </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__complex__"> object.__complex__(self)<a class="headerlink" href="#object.__complex__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__int__"> object.__int__(self)<a class="headerlink" href="#object.__int__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__float__"> object.__float__(self)<a class="headerlink" href="#object.__float__" title="Link to this definition">¶</a></dt> <dd>Called to implement the built-in functions <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-func docutils literal notranslate">complex()</code></a>, <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate">int()</code></a> and <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-func docutils literal notranslate">float()</code></a>. Should return a value of the appropriate type. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__index__"> object.__index__(self)<a class="headerlink" href="#object.__index__" title="Link to this definition">¶</a></dt> <dd>Called to implement <a class="reference internal" href="../library/operator.html#operator.index" title="operator.index"><code class="xref py py-func docutils literal notranslate">operator.index()</code></a>, and whenever Python needs to losslessly convert the numeric object to an integer object (such as in slicing, or in the built-in <a class="reference internal" href="../library/functions.html#bin" title="bin"><code class="xref py py-func docutils literal notranslate">bin()</code></a>, <a class="reference internal" href="../library/functions.html#hex" title="hex"><code class="xref py py-func docutils literal notranslate">hex()</code></a> and <a class="reference internal" href="../library/functions.html#oct" title="oct"><code class="xref py py-func docutils literal notranslate">oct()</code></a> functions). Presence of this method indicates that the numeric object is an integer type. Must return an integer. If <a class="reference internal" href="#object.__int__" title="object.__int__"><code class="xref py py-meth docutils literal notranslate">__int__()</code></a>, <a class="reference internal" href="#object.__float__" title="object.__float__"><code class="xref py py-meth docutils literal notranslate">__float__()</code></a> and <a class="reference internal" href="#object.__complex__" title="object.__complex__"><code class="xref py py-meth docutils literal notranslate">__complex__()</code></a> are not defined then corresponding built-in functions <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate">int()</code></a>, <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-func docutils literal notranslate">float()</code></a> and <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-func docutils literal notranslate">complex()</code></a> fall back to <a class="reference internal" href="#object.__index__" title="object.__index__"><code class="xref py py-meth docutils literal notranslate">__index__()</code></a>. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__round__"> object.__round__(self[, ndigits])<a class="headerlink" href="#object.__round__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__trunc__"> object.__trunc__(self)<a class="headerlink" href="#object.__trunc__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__floor__"> object.__floor__(self)<a class="headerlink" href="#object.__floor__" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="object.__ceil__"> object.__ceil__(self)<a class="headerlink" href="#object.__ceil__" title="Link to this definition">¶</a></dt> <dd>Called to implement the built-in function <a class="reference internal" href="../library/functions.html#round" title="round"><code class="xref py py-func docutils literal notranslate">round()</code></a> and <a class="reference internal" href="../library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate">math</code></a> functions <a class="reference internal" href="../library/math.html#math.trunc" title="math.trunc"><code class="xref py py-func docutils literal notranslate">trunc()</code></a>, <a class="reference internal" href="../library/math.html#math.floor" title="math.floor"><code class="xref py py-func docutils literal notranslate">floor()</code></a> and <a class="reference internal" href="../library/math.html#math.ceil" title="math.ceil"><code class="xref py py-func docutils literal notranslate">ceil()</code></a>. Unless ndigits is passed to <code class="xref py py-meth docutils literal notranslate">__round__()</code> all these methods should return the value of the object truncated to an <a class="reference internal" href="../library/numbers.html#numbers.Integral" title="numbers.Integral"><code class="xref py py-class docutils literal notranslate">Integral</code></a> (typically an <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>). The built-in function <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate">int()</code></a> falls back to <a class="reference internal" href="#object.__trunc__" title="object.__trunc__"><code class="xref py py-meth docutils literal notranslate">__trunc__()</code></a> if neither <a class="reference internal" href="#object.__int__" title="object.__int__"><code class="xref py py-meth docutils literal notranslate">__int__()</code></a> nor <a class="reference internal" href="#object.__index__" title="object.__index__"><code class="xref py py-meth docutils literal notranslate">__index__()</code></a> is defined. <div class="versionchanged"> Changed in version 3.11: The delegation of <a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-func docutils literal notranslate">int()</code></a> to <a class="reference internal" href="#object.__trunc__" title="object.__trunc__"><code class="xref py py-meth docutils literal notranslate">__trunc__()</code></a> is deprecated. </div> </dd></dl> </section> <section id="with-statement-context-managers"> <h3>3.3.9. With Statement Context Managers<a class="headerlink" href="#with-statement-context-managers" title="Link to this heading">¶</a></h3> A context manager is an object that defines the runtime context to be established when executing a <a class="reference internal" href="compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement. The context manager handles the entry into, and the exit from, the desired runtime context for the execution of the block of code. Context managers are normally invoked using the <code class="xref std std-keyword docutils literal notranslate">with</code> statement (described in section <a class="reference internal" href="compound_stmts.html#with">The with statement</a>), but can also be used by directly invoking their methods. Typical uses of context managers include saving and restoring various kinds of global state, locking and unlocking resources, closing opened files, etc. For more information on context managers, see <a class="reference internal" href="../library/stdtypes.html#typecontextmanager">Context Manager Types</a>. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not provide the context manager methods. <dl class="py method"> <dt class="sig sig-object py" id="object.__enter__"> object.__enter__(self)<a class="headerlink" href="#object.__enter__" title="Link to this definition">¶</a></dt> <dd>Enter the runtime context related to this object. The <a class="reference internal" href="compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement will bind this method’s return value to the target(s) specified in the <code class="xref std std-keyword docutils literal notranslate">as</code> clause of the statement, if any. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__exit__"> object.__exit__(self, exc_type, exc_value, traceback)<a class="headerlink" href="#object.__exit__" title="Link to this definition">¶</a></dt> <dd>Exit the runtime context related to this object. The parameters describe the exception that caused the context to be exited. If the context was exited without an exception, all three arguments will be <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate">None</code></a>. If an exception is supplied, and the method wishes to suppress the exception (i.e., prevent it from being propagated), it should return a true value. Otherwise, the exception will be processed normally upon exit from this method. Note that <a class="reference internal" href="#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate">__exit__()</code></a> methods should not reraise the passed-in exception; this is the caller’s responsibility. </dd></dl> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0343/">PEP 343</a> - The “with” statement</dt><dd>The specification, background, and examples for the Python <a class="reference internal" href="compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement. </dd> </dl> </div> </section> <section id="customizing-positional-arguments-in-class-pattern-matching"> <h3>3.3.10. Customizing positional arguments in class pattern matching<a class="headerlink" href="#customizing-positional-arguments-in-class-pattern-matching" title="Link to this heading">¶</a></h3> When using a class name in a pattern, positional arguments in the pattern are not allowed by default, i.e. <code class="docutils literal notranslate">case MyClass(x, y)</code> is typically invalid without special support in <code class="docutils literal notranslate">MyClass</code>. To be able to use that kind of pattern, the class needs to define a __match_args__ attribute. <dl class="py data"> <dt class="sig sig-object py" id="object.__match_args__"> object.__match_args__<a class="headerlink" href="#object.__match_args__" title="Link to this definition">¶</a></dt> <dd>This class variable can be assigned a tuple of strings. When this class is used in a class pattern with positional arguments, each positional argument will be converted into a keyword argument, using the corresponding value in __match_args__ as the keyword. The absence of this attribute is equivalent to setting it to <code class="docutils literal notranslate">()</code>. </dd></dl> For example, if <code class="docutils literal notranslate">MyClass.__match_args__</code> is <code class="docutils literal notranslate">("left", "center", "right")</code> that means that <code class="docutils literal notranslate">case MyClass(x, y)</code> is equivalent to <code class="docutils literal notranslate">case MyClass(left=x, center=y)</code>. Note that the number of arguments in the pattern must be smaller than or equal to the number of elements in __match_args__; if it is larger, the pattern match attempt will raise a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>. <div class="versionadded"> Added in version 3.10. </div> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0634/">PEP 634</a> - Structural Pattern Matching</dt><dd>The specification for the Python <code class="docutils literal notranslate">match</code> statement. </dd> </dl> </div> </section> <section id="emulating-buffer-types"> <h3>3.3.11. Emulating buffer types<a class="headerlink" href="#emulating-buffer-types" title="Link to this heading">¶</a></h3> The <a class="reference internal" href="../c-api/buffer.html#bufferobjects">buffer protocol</a> provides a way for Python objects to expose efficient access to a low-level memory array. This protocol is implemented by builtin types such as <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> and <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a>, and third-party libraries may define additional buffer types. While buffer types are usually implemented in C, it is also possible to implement the protocol in Python. <dl class="py method"> <dt class="sig sig-object py" id="object.__buffer__"> object.__buffer__(self, flags)<a class="headerlink" href="#object.__buffer__" title="Link to this definition">¶</a></dt> <dd>Called when a buffer is requested from self (for example, by the <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> constructor). The flags argument is an integer representing the kind of buffer requested, affecting for example whether the returned buffer is read-only or writable. <a class="reference internal" href="../library/inspect.html#inspect.BufferFlags" title="inspect.BufferFlags"><code class="xref py py-class docutils literal notranslate">inspect.BufferFlags</code></a> provides a convenient way to interpret the flags. The method must return a <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> object. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__release_buffer__"> object.__release_buffer__(self, buffer)<a class="headerlink" href="#object.__release_buffer__" title="Link to this definition">¶</a></dt> <dd>Called when a buffer is no longer needed. The buffer argument is a <a class="reference internal" href="../library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> object that was previously returned by <a class="reference internal" href="#object.__buffer__" title="object.__buffer__"><code class="xref py py-meth docutils literal notranslate">__buffer__()</code></a>. The method must release any resources associated with the buffer. This method should return <code class="docutils literal notranslate">None</code>. Buffer objects that do not need to perform any cleanup are not required to implement this method. </dd></dl> <div class="versionadded"> Added in version 3.12. </div> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0688/">PEP 688</a> - Making the buffer protocol accessible in Python</dt><dd>Introduces the Python <code class="docutils literal notranslate">__buffer__</code> and <code class="docutils literal notranslate">__release_buffer__</code> methods. </dd> <dt><a class="reference internal" href="../library/collections.abc.html#collections.abc.Buffer" title="collections.abc.Buffer"><code class="xref py py-class docutils literal notranslate">collections.abc.Buffer</code></a></dt><dd>ABC for buffer types. </dd> </dl> </div> </section> <section id="special-method-lookup"> <h3>3.3.12. Special method lookup<a class="headerlink" href="#special-method-lookup" title="Link to this heading">¶</a></h3> For custom classes, implicit invocations of special methods are only guaranteed to work correctly if defined on an object’s type, not in the object’s instance dictionary. That behaviour is the reason why the following code raises an exception: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class C: ... pass ... >>> c = C() >>> c.__len__ = lambda: 5 >>> len(c) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: object of type 'C' has no len() </pre></div> </div> The rationale behind this behaviour lies with a number of special methods such as <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> and <a class="reference internal" href="#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate">__repr__()</code></a> that are implemented by all objects, including type objects. If the implicit lookup of these methods used the conventional lookup process, they would fail when invoked on the type object itself: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> 1 .__hash__() == hash(1) True >>> int.__hash__() == hash(int) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: descriptor '__hash__' of 'int' object needs an argument </pre></div> </div> Incorrectly attempting to invoke an unbound method of a class in this way is sometimes referred to as ‘metaclass confusion’, and is avoided by bypassing the instance when looking up special methods: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> type(1).__hash__(1) == hash(1) True >>> type(int).__hash__(int) == hash(int) True </pre></div> </div> In addition to bypassing any instance attributes in the interest of correctness, implicit special method lookup generally also bypasses the <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a> method even of the object’s metaclass: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class Meta(type): ... def __getattribute__(*args): ... print("Metaclass getattribute invoked") ... return type.__getattribute__(*args) ... >>> class C(object, metaclass=Meta): ... def __len__(self): ... return 10 ... def __getattribute__(*args): ... print("Class getattribute invoked") ... return object.__getattribute__(*args) ... >>> c = C() >>> c.__len__() # Explicit lookup via instance Class getattribute invoked 10 >>> type(c).__len__(c) # Explicit lookup via type Metaclass getattribute invoked 10 >>> len(c) # Implicit lookup 10 </pre></div> </div> Bypassing the <a class="reference internal" href="#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a> machinery in this fashion provides significant scope for speed optimisations within the interpreter, at the cost of some flexibility in the handling of special methods (the special method must be set on the class object itself in order to be consistently invoked by the interpreter). </section> </section> <section id="coroutines"> <h2>3.4. Coroutines<a class="headerlink" href="#coroutines" title="Link to this heading">¶</a></h2> <section id="awaitable-objects"> <h3>3.4.1. Awaitable Objects<a class="headerlink" href="#awaitable-objects" title="Link to this heading">¶</a></h3> An <a class="reference internal" href="../glossary.html#term-awaitable">awaitable</a> object generally implements an <a class="reference internal" href="#object.__await__" title="object.__await__"><code class="xref py py-meth docutils literal notranslate">__await__()</code></a> method. <a class="reference internal" href="../glossary.html#term-coroutine">Coroutine objects</a> returned from <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate">async def</code></a> functions are awaitable. <div class="admonition note"> Note The <a class="reference internal" href="../glossary.html#term-generator-iterator">generator iterator</a> objects returned from generators decorated with <a class="reference internal" href="../library/types.html#types.coroutine" title="types.coroutine"><code class="xref py py-func docutils literal notranslate">types.coroutine()</code></a> are also awaitable, but they do not implement <a class="reference internal" href="#object.__await__" title="object.__await__"><code class="xref py py-meth docutils literal notranslate">__await__()</code></a>. </div> <dl class="py method"> <dt class="sig sig-object py" id="object.__await__"> object.__await__(self)<a class="headerlink" href="#object.__await__" title="Link to this definition">¶</a></dt> <dd>Must return an <a class="reference internal" href="../glossary.html#term-iterator">iterator</a>. Should be used to implement <a class="reference internal" href="../glossary.html#term-awaitable">awaitable</a> objects. For instance, <a class="reference internal" href="../library/asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate">asyncio.Future</code></a> implements this method to be compatible with the <a class="reference internal" href="expressions.html#await"><code class="xref std std-keyword docutils literal notranslate">await</code></a> expression. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself is not awaitable and does not provide this method. <div class="admonition note"> Note The language doesn’t place any restriction on the type or value of the objects yielded by the iterator returned by <code class="docutils literal notranslate">__await__</code>, as this is specific to the implementation of the asynchronous execution framework (e.g. <a class="reference internal" href="../library/asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate">asyncio</code></a>) that will be managing the <a class="reference internal" href="../glossary.html#term-awaitable">awaitable</a> object. </div> </dd></dl> <div class="versionadded"> Added in version 3.5. </div> <div class="admonition seealso"> See also <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a> for additional information about awaitable objects. </div> </section> <section id="coroutine-objects"> <h3>3.4.2. Coroutine Objects<a class="headerlink" href="#coroutine-objects" title="Link to this heading">¶</a></h3> <a class="reference internal" href="../glossary.html#term-coroutine">Coroutine objects</a> are <a class="reference internal" href="../glossary.html#term-awaitable">awaitable</a> objects. A coroutine’s execution can be controlled by calling <a class="reference internal" href="#object.__await__" title="object.__await__"><code class="xref py py-meth docutils literal notranslate">__await__()</code></a> and iterating over the result. When the coroutine has finished executing and returns, the iterator raises <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a>, and the exception’s <a class="reference internal" href="../library/exceptions.html#StopIteration.value" title="StopIteration.value"><code class="xref py py-attr docutils literal notranslate">value</code></a> attribute holds the return value. If the coroutine raises an exception, it is propagated by the iterator. Coroutines should not directly raise unhandled <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a> exceptions. Coroutines also have the methods listed below, which are analogous to those of generators (see <a class="reference internal" href="expressions.html#generator-methods">Generator-iterator methods</a>). However, unlike generators, coroutines do not directly support iteration. <div class="versionchanged"> Changed in version 3.5.2: It is a <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate">RuntimeError</code></a> to await on a coroutine more than once. </div> <dl class="py method"> <dt class="sig sig-object py" id="coroutine.send"> coroutine.send(value)<a class="headerlink" href="#coroutine.send" title="Link to this definition">¶</a></dt> <dd>Starts or resumes execution of the coroutine. If value is <code class="docutils literal notranslate">None</code>, this is equivalent to advancing the iterator returned by <a class="reference internal" href="#object.__await__" title="object.__await__"><code class="xref py py-meth docutils literal notranslate">__await__()</code></a>. If value is not <code class="docutils literal notranslate">None</code>, this method delegates to the <a class="reference internal" href="expressions.html#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate">send()</code></a> method of the iterator that caused the coroutine to suspend. The result (return value, <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a>, or other exception) is the same as when iterating over the <code class="xref py py-meth docutils literal notranslate">__await__()</code> return value, described above. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="coroutine.throw"> coroutine.throw(value)<a class="headerlink" href="#coroutine.throw" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py"> coroutine.throw(type[, value[, traceback]])</dt> <dd>Raises the specified exception in the coroutine. This method delegates to the <a class="reference internal" href="expressions.html#generator.throw" title="generator.throw"><code class="xref py py-meth docutils literal notranslate">throw()</code></a> method of the iterator that caused the coroutine to suspend, if it has such a method. Otherwise, the exception is raised at the suspension point. The result (return value, <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a>, or other exception) is the same as when iterating over the <a class="reference internal" href="#object.__await__" title="object.__await__"><code class="xref py py-meth docutils literal notranslate">__await__()</code></a> return value, described above. If the exception is not caught in the coroutine, it propagates back to the caller. <div class="versionchanged"> Changed in version 3.12: The second signature (type[, value[, traceback]]) is deprecated and may be removed in a future version of Python. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="coroutine.close"> coroutine.close()<a class="headerlink" href="#coroutine.close" title="Link to this definition">¶</a></dt> <dd>Causes the coroutine to clean itself up and exit. If the coroutine is suspended, this method first delegates to the <a class="reference internal" href="expressions.html#generator.close" title="generator.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a> method of the iterator that caused the coroutine to suspend, if it has such a method. Then it raises <a class="reference internal" href="../library/exceptions.html#GeneratorExit" title="GeneratorExit"><code class="xref py py-exc docutils literal notranslate">GeneratorExit</code></a> at the suspension point, causing the coroutine to immediately clean itself up. Finally, the coroutine is marked as having finished executing, even if it was never started. Coroutine objects are automatically closed using the above process when they are about to be destroyed. </dd></dl> </section> <section id="asynchronous-iterators"> <h3>3.4.3. Asynchronous Iterators<a class="headerlink" href="#asynchronous-iterators" title="Link to this heading">¶</a></h3> An asynchronous iterator can call asynchronous code in its <code class="docutils literal notranslate">__anext__</code> method. Asynchronous iterators can be used in an <a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a> statement. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not provide these methods. <dl class="py method"> <dt class="sig sig-object py" id="object.__aiter__"> object.__aiter__(self)<a class="headerlink" href="#object.__aiter__" title="Link to this definition">¶</a></dt> <dd>Must return an asynchronous iterator object. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__anext__"> object.__anext__(self)<a class="headerlink" href="#object.__anext__" title="Link to this definition">¶</a></dt> <dd>Must return an awaitable resulting in a next value of the iterator. Should raise a <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate">StopAsyncIteration</code></a> error when the iteration is over. </dd></dl> An example of an asynchronous iterable object: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Reader: async def readline(self): ... def __aiter__(self): return self async def __anext__(self): val = await self.readline() if val == b'': raise StopAsyncIteration return val </pre></div> </div> <div class="versionadded"> Added in version 3.5. </div> <div class="versionchanged"> Changed in version 3.7: Prior to Python 3.7, <a class="reference internal" href="#object.__aiter__" title="object.__aiter__"><code class="xref py py-meth docutils literal notranslate">__aiter__()</code></a> could return an awaitable that would resolve to an <a class="reference internal" href="../glossary.html#term-asynchronous-iterator">asynchronous iterator</a>. Starting with Python 3.7, <a class="reference internal" href="#object.__aiter__" title="object.__aiter__"><code class="xref py py-meth docutils literal notranslate">__aiter__()</code></a> must return an asynchronous iterator object. Returning anything else will result in a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> error. </div> </section> <section id="asynchronous-context-managers"> <h3>3.4.4. Asynchronous Context Managers<a class="headerlink" href="#asynchronous-context-managers" title="Link to this heading">¶</a></h3> An asynchronous context manager is a context manager that is able to suspend execution in its <code class="docutils literal notranslate">__aenter__</code> and <code class="docutils literal notranslate">__aexit__</code> methods. Asynchronous context managers can be used in an <a class="reference internal" href="compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate">async with</code></a> statement. The <a class="reference internal" href="../library/functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> class itself does not provide these methods. <dl class="py method"> <dt class="sig sig-object py" id="object.__aenter__"> object.__aenter__(self)<a class="headerlink" href="#object.__aenter__" title="Link to this definition">¶</a></dt> <dd>Semantically similar to <a class="reference internal" href="#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate">__enter__()</code></a>, the only difference being that it must return an awaitable. </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="object.__aexit__"> object.__aexit__(self, exc_type, exc_value, traceback)<a class="headerlink" href="#object.__aexit__" title="Link to this definition">¶</a></dt> <dd>Semantically similar to <a class="reference internal" href="#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate">__exit__()</code></a>, the only difference being that it must return an awaitable. </dd></dl> An example of an asynchronous context manager class: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class AsyncContextManager: async def __aenter__(self): await log('entering context') async def __aexit__(self, exc_type, exc, tb): await log('exiting context') </pre></div> </div> <div class="versionadded"> Added in version 3.5. </div> Footnotes <aside class="footnote-list brackets"> <aside class="footnote brackets" id="id19" role="doc-footnote"> [<a role="doc-backlink" href="#id1">1</a>] It is possible in some cases to change an object’s type, under certain controlled conditions. It generally isn’t a good idea though, since it can lead to some very strange behaviour if it is handled incorrectly. </aside> <aside class="footnote brackets" id="id20" role="doc-footnote"> [<a role="doc-backlink" href="#id12">2</a>] The <a class="reference internal" href="#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a>, <a class="reference internal" href="#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a>, <a class="reference internal" href="#object.__reversed__" title="object.__reversed__"><code class="xref py py-meth docutils literal notranslate">__reversed__()</code></a>, <a class="reference internal" href="#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate">__contains__()</code></a>, <a class="reference internal" href="#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> and <a class="reference internal" href="../library/os.html#os.PathLike.__fspath__" title="os.PathLike.__fspath__"><code class="xref py py-meth docutils literal notranslate">__fspath__()</code></a> methods have special handling for this. Others will still raise a <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>, but may do so by relying on the behavior that <code class="docutils literal notranslate">None</code> is not callable. </aside> <aside class="footnote brackets" id="id21" role="doc-footnote"> [<a role="doc-backlink" href="#id16">3</a>] “Does not support” here means that the class has no such method, or the method returns <a class="reference internal" href="../library/constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate">NotImplemented</code></a>. Do not set the method to <code class="docutils literal notranslate">None</code> if you want to force fallback to the right operand’s reflected method—that will instead have the opposite effect of explicitly blocking such fallback. </aside> <aside class="footnote brackets" id="id22" role="doc-footnote"> [<a role="doc-backlink" href="#id17">4</a>] For operands of the same type, it is assumed that if the non-reflected method – such as <a class="reference internal" href="#object.__add__" title="object.__add__"><code class="xref py py-meth docutils literal notranslate">__add__()</code></a> – fails then the overall operation is not supported, which is why the reflected method is not called. </aside> </aside> </section> </section> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">3. Data model</a><ul> <li><a class="reference internal" href="#objects-values-and-types">3.1. Objects, values and types</a></li> <li><a class="reference internal" href="#the-standard-type-hierarchy">3.2. The standard type hierarchy</a><ul> <li><a class="reference internal" href="#none">3.2.1. None</a></li> <li><a class="reference internal" href="#notimplemented">3.2.2. NotImplemented</a></li> <li><a class="reference internal" href="#ellipsis">3.2.3. Ellipsis</a></li> <li><a class="reference internal" href="#numbers-number">3.2.4. <code class="xref py py-class docutils literal notranslate">numbers.Number</code></a><ul> <li><a class="reference internal" href="#numbers-integral">3.2.4.1. <code class="xref py py-class docutils literal notranslate">numbers.Integral</code></a></li> <li><a class="reference internal" href="#numbers-real-float">3.2.4.2. <code class="xref py py-class docutils literal notranslate">numbers.Real</code> (<code class="xref py py-class docutils literal notranslate">float</code>)</a></li> <li><a class="reference internal" href="#numbers-complex-complex">3.2.4.3. <code class="xref py py-class docutils literal notranslate">numbers.Complex</code> (<code class="xref py py-class docutils literal notranslate">complex</code>)</a></li> </ul> </li> <li><a class="reference internal" href="#sequences">3.2.5. Sequences</a><ul> <li><a class="reference internal" href="#immutable-sequences">3.2.5.1. Immutable sequences</a></li> <li><a class="reference internal" href="#mutable-sequences">3.2.5.2. Mutable sequences</a></li> </ul> </li> <li><a class="reference internal" href="#set-types">3.2.6. Set types</a></li> <li><a class="reference internal" href="#mappings">3.2.7. Mappings</a><ul> <li><a class="reference internal" href="#dictionaries">3.2.7.1. Dictionaries</a></li> </ul> </li> <li><a class="reference internal" href="#callable-types">3.2.8. Callable types</a><ul> <li><a class="reference internal" href="#user-defined-functions">3.2.8.1. User-defined functions</a><ul> <li><a class="reference internal" href="#special-read-only-attributes">3.2.8.1.1. Special read-only attributes</a><ul> <li><a class="reference internal" href="#function.__globals__"><code class="docutils literal notranslate">__globals__</code></a></li> <li><a class="reference internal" href="#function.__closure__"><code class="docutils literal notranslate">__closure__</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-writable-attributes">3.2.8.1.2. Special writable attributes</a><ul> <li><a class="reference internal" href="#function.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#function.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#function.__qualname__"><code class="docutils literal notranslate">__qualname__</code></a></li> <li><a class="reference internal" href="#function.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#function.__defaults__"><code class="docutils literal notranslate">__defaults__</code></a></li> <li><a class="reference internal" href="#function.__code__"><code class="docutils literal notranslate">__code__</code></a></li> <li><a class="reference internal" href="#function.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> <li><a class="reference internal" href="#function.__annotations__"><code class="docutils literal notranslate">__annotations__</code></a></li> <li><a class="reference internal" href="#function.__kwdefaults__"><code class="docutils literal notranslate">__kwdefaults__</code></a></li> <li><a class="reference internal" href="#function.__type_params__"><code class="docutils literal notranslate">__type_params__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#instance-methods">3.2.8.2. Instance methods</a><ul> <li><a class="reference internal" href="#method.__self__"><code class="docutils literal notranslate">__self__</code></a></li> <li><a class="reference internal" href="#method.__func__"><code class="docutils literal notranslate">__func__</code></a></li> <li><a class="reference internal" href="#method.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#method.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#method.__module__"><code class="docutils literal notranslate">__module__</code></a></li> </ul> </li> <li><a class="reference internal" href="#generator-functions">3.2.8.3. Generator functions</a></li> <li><a class="reference internal" href="#coroutine-functions">3.2.8.4. Coroutine functions</a></li> <li><a class="reference internal" href="#asynchronous-generator-functions">3.2.8.5. Asynchronous generator functions</a></li> <li><a class="reference internal" href="#built-in-functions">3.2.8.6. Built-in functions</a></li> <li><a class="reference internal" href="#built-in-methods">3.2.8.7. Built-in methods</a></li> <li><a class="reference internal" href="#classes">3.2.8.8. Classes</a></li> <li><a class="reference internal" href="#class-instances">3.2.8.9. Class Instances</a></li> </ul> </li> <li><a class="reference internal" href="#modules">3.2.9. Modules</a><ul> <li><a class="reference internal" href="#import-related-attributes-on-module-objects">3.2.9.1. Import-related attributes on module objects</a><ul> <li><a class="reference internal" href="#module.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#module.__spec__"><code class="docutils literal notranslate">__spec__</code></a></li> <li><a class="reference internal" href="#module.__package__"><code class="docutils literal notranslate">__package__</code></a></li> <li><a class="reference internal" href="#module.__loader__"><code class="docutils literal notranslate">__loader__</code></a></li> <li><a class="reference internal" href="#module.__path__"><code class="docutils literal notranslate">__path__</code></a></li> <li><a class="reference internal" href="#module.__file__"><code class="docutils literal notranslate">__file__</code></a></li> <li><a class="reference internal" href="#module.__cached__"><code class="docutils literal notranslate">__cached__</code></a></li> </ul> </li> <li><a class="reference internal" href="#other-writable-attributes-on-module-objects">3.2.9.2. Other writable attributes on module objects</a><ul> <li><a class="reference internal" href="#module.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#module.__annotations__"><code class="docutils literal notranslate">__annotations__</code></a></li> </ul> </li> <li><a class="reference internal" href="#module-dictionaries">3.2.9.3. Module dictionaries</a><ul> <li><a class="reference internal" href="#module.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#custom-classes">3.2.10. Custom classes</a><ul> <li><a class="reference internal" href="#special-attributes">3.2.10.1. Special attributes</a><ul> <li><a class="reference internal" href="#type.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#type.__qualname__"><code class="docutils literal notranslate">__qualname__</code></a></li> <li><a class="reference internal" href="#type.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#type.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> <li><a class="reference internal" href="#type.__bases__"><code class="docutils literal notranslate">__bases__</code></a></li> <li><a class="reference internal" href="#type.__doc__"><code class="docutils literal notranslate">__doc__</code></a></li> <li><a class="reference internal" href="#type.__annotations__"><code class="docutils literal notranslate">__annotations__</code></a></li> <li><a class="reference internal" href="#type.__type_params__"><code class="docutils literal notranslate">__type_params__</code></a></li> <li><a class="reference internal" href="#type.__static_attributes__"><code class="docutils literal notranslate">__static_attributes__</code></a></li> <li><a class="reference internal" href="#type.__firstlineno__"><code class="docutils literal notranslate">__firstlineno__</code></a></li> <li><a class="reference internal" href="#type.__mro__"><code class="docutils literal notranslate">__mro__</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-methods">3.2.10.2. Special methods</a><ul> <li><a class="reference internal" href="#type.mro"><code class="docutils literal notranslate">mro()</code></a></li> <li><a class="reference internal" href="#type.__subclasses__"><code class="docutils literal notranslate">__subclasses__()</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#id4">3.2.11. Class instances</a><ul> <li><a class="reference internal" href="#id5">3.2.11.1. Special attributes</a><ul> <li><a class="reference internal" href="#object.__class__"><code class="docutils literal notranslate">__class__</code></a></li> <li><a class="reference internal" href="#object.__dict__"><code class="docutils literal notranslate">__dict__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#i-o-objects-also-known-as-file-objects">3.2.12. I/O objects (also known as file objects)</a></li> <li><a class="reference internal" href="#internal-types">3.2.13. Internal types</a><ul> <li><a class="reference internal" href="#code-objects">3.2.13.1. Code objects</a><ul> <li><a class="reference internal" href="#index-60">3.2.13.1.1. Special read-only attributes</a><ul> <li><a class="reference internal" href="#codeobject.co_name"><code class="docutils literal notranslate">co_name</code></a></li> <li><a class="reference internal" href="#codeobject.co_qualname"><code class="docutils literal notranslate">co_qualname</code></a></li> <li><a class="reference internal" href="#codeobject.co_argcount"><code class="docutils literal notranslate">co_argcount</code></a></li> <li><a class="reference internal" href="#codeobject.co_posonlyargcount"><code class="docutils literal notranslate">co_posonlyargcount</code></a></li> <li><a class="reference internal" href="#codeobject.co_kwonlyargcount"><code class="docutils literal notranslate">co_kwonlyargcount</code></a></li> <li><a class="reference internal" href="#codeobject.co_nlocals"><code class="docutils literal notranslate">co_nlocals</code></a></li> <li><a class="reference internal" href="#codeobject.co_varnames"><code class="docutils literal notranslate">co_varnames</code></a></li> <li><a class="reference internal" href="#codeobject.co_cellvars"><code class="docutils literal notranslate">co_cellvars</code></a></li> <li><a class="reference internal" href="#codeobject.co_freevars"><code class="docutils literal notranslate">co_freevars</code></a></li> <li><a class="reference internal" href="#codeobject.co_code"><code class="docutils literal notranslate">co_code</code></a></li> <li><a class="reference internal" href="#codeobject.co_consts"><code class="docutils literal notranslate">co_consts</code></a></li> <li><a class="reference internal" href="#codeobject.co_names"><code class="docutils literal notranslate">co_names</code></a></li> <li><a class="reference internal" href="#codeobject.co_filename"><code class="docutils literal notranslate">co_filename</code></a></li> <li><a class="reference internal" href="#codeobject.co_firstlineno"><code class="docutils literal notranslate">co_firstlineno</code></a></li> <li><a class="reference internal" href="#codeobject.co_lnotab"><code class="docutils literal notranslate">co_lnotab</code></a></li> <li><a class="reference internal" href="#codeobject.co_stacksize"><code class="docutils literal notranslate">co_stacksize</code></a></li> <li><a class="reference internal" href="#codeobject.co_flags"><code class="docutils literal notranslate">co_flags</code></a></li> </ul> </li> <li><a class="reference internal" href="#methods-on-code-objects">3.2.13.1.2. Methods on code objects</a><ul> <li><a class="reference internal" href="#codeobject.co_positions"><code class="docutils literal notranslate">co_positions()</code></a></li> <li><a class="reference internal" href="#codeobject.co_lines"><code class="docutils literal notranslate">co_lines()</code></a></li> <li><a class="reference internal" href="#codeobject.replace"><code class="docutils literal notranslate">replace()</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#frame-objects">3.2.13.2. Frame objects</a><ul> <li><a class="reference internal" href="#index-66">3.2.13.2.1. Special read-only attributes</a><ul> <li><a class="reference internal" href="#frame.f_back"><code class="docutils literal notranslate">f_back</code></a></li> <li><a class="reference internal" href="#frame.f_code"><code class="docutils literal notranslate">f_code</code></a></li> <li><a class="reference internal" href="#frame.f_locals"><code class="docutils literal notranslate">f_locals</code></a></li> <li><a class="reference internal" href="#frame.f_globals"><code class="docutils literal notranslate">f_globals</code></a></li> <li><a class="reference internal" href="#frame.f_builtins"><code class="docutils literal notranslate">f_builtins</code></a></li> <li><a class="reference internal" href="#frame.f_lasti"><code class="docutils literal notranslate">f_lasti</code></a></li> </ul> </li> <li><a class="reference internal" href="#index-67">3.2.13.2.2. Special writable attributes</a><ul> <li><a class="reference internal" href="#frame.f_trace"><code class="docutils literal notranslate">f_trace</code></a></li> <li><a class="reference internal" href="#frame.f_trace_lines"><code class="docutils literal notranslate">f_trace_lines</code></a></li> <li><a class="reference internal" href="#frame.f_trace_opcodes"><code class="docutils literal notranslate">f_trace_opcodes</code></a></li> <li><a class="reference internal" href="#frame.f_lineno"><code class="docutils literal notranslate">f_lineno</code></a></li> </ul> </li> <li><a class="reference internal" href="#frame-object-methods">3.2.13.2.3. Frame object methods</a><ul> <li><a class="reference internal" href="#frame.clear"><code class="docutils literal notranslate">clear()</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#traceback-objects">3.2.13.3. Traceback objects</a><ul> <li><a class="reference internal" href="#traceback.tb_frame"><code class="docutils literal notranslate">tb_frame</code></a></li> <li><a class="reference internal" href="#traceback.tb_lineno"><code class="docutils literal notranslate">tb_lineno</code></a></li> <li><a class="reference internal" href="#traceback.tb_lasti"><code class="docutils literal notranslate">tb_lasti</code></a></li> <li><a class="reference internal" href="#traceback.tb_next"><code class="docutils literal notranslate">tb_next</code></a></li> </ul> </li> <li><a class="reference internal" href="#slice-objects">3.2.13.4. Slice objects</a><ul> <li><a class="reference internal" href="#slice.indices"><code class="docutils literal notranslate">indices()</code></a></li> </ul> </li> <li><a class="reference internal" href="#static-method-objects">3.2.13.5. Static method objects</a></li> <li><a class="reference internal" href="#class-method-objects">3.2.13.6. Class method objects</a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#special-method-names">3.3. Special method names</a><ul> <li><a class="reference internal" href="#basic-customization">3.3.1. Basic customization</a><ul> <li><a class="reference internal" href="#object.__new__"><code class="docutils literal notranslate">__new__()</code></a></li> <li><a class="reference internal" href="#object.__init__"><code class="docutils literal notranslate">__init__()</code></a></li> <li><a class="reference internal" href="#object.__del__"><code class="docutils literal notranslate">__del__()</code></a></li> <li><a class="reference internal" href="#object.__repr__"><code class="docutils literal notranslate">__repr__()</code></a></li> <li><a class="reference internal" href="#object.__str__"><code class="docutils literal notranslate">__str__()</code></a></li> <li><a class="reference internal" href="#object.__bytes__"><code class="docutils literal notranslate">__bytes__()</code></a></li> <li><a class="reference internal" href="#object.__format__"><code class="docutils literal notranslate">__format__()</code></a></li> <li><a class="reference internal" href="#object.__lt__"><code class="docutils literal notranslate">__lt__()</code></a></li> <li><a class="reference internal" href="#object.__le__"><code class="docutils literal notranslate">__le__()</code></a></li> <li><a class="reference internal" href="#object.__eq__"><code class="docutils literal notranslate">__eq__()</code></a></li> <li><a class="reference internal" href="#object.__ne__"><code class="docutils literal notranslate">__ne__()</code></a></li> <li><a class="reference internal" href="#object.__gt__"><code class="docutils literal notranslate">__gt__()</code></a></li> <li><a class="reference internal" href="#object.__ge__"><code class="docutils literal notranslate">__ge__()</code></a></li> <li><a class="reference internal" href="#object.__hash__"><code class="docutils literal notranslate">__hash__()</code></a></li> <li><a class="reference internal" href="#object.__bool__"><code class="docutils literal notranslate">__bool__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#customizing-attribute-access">3.3.2. Customizing attribute access</a><ul> <li><a class="reference internal" href="#object.__getattr__"><code class="docutils literal notranslate">__getattr__()</code></a></li> <li><a class="reference internal" href="#object.__getattribute__"><code class="docutils literal notranslate">__getattribute__()</code></a></li> <li><a class="reference internal" href="#object.__setattr__"><code class="docutils literal notranslate">__setattr__()</code></a></li> <li><a class="reference internal" href="#object.__delattr__"><code class="docutils literal notranslate">__delattr__()</code></a></li> <li><a class="reference internal" href="#object.__dir__"><code class="docutils literal notranslate">__dir__()</code></a></li> <li><a class="reference internal" href="#customizing-module-attribute-access">3.3.2.1. Customizing module attribute access</a></li> <li><a class="reference internal" href="#implementing-descriptors">3.3.2.2. Implementing Descriptors</a><ul> <li><a class="reference internal" href="#object.__get__"><code class="docutils literal notranslate">__get__()</code></a></li> <li><a class="reference internal" href="#object.__set__"><code class="docutils literal notranslate">__set__()</code></a></li> <li><a class="reference internal" href="#object.__delete__"><code class="docutils literal notranslate">__delete__()</code></a></li> <li><a class="reference internal" href="#object.__objclass__"><code class="docutils literal notranslate">__objclass__</code></a></li> </ul> </li> <li><a class="reference internal" href="#invoking-descriptors">3.3.2.3. Invoking Descriptors</a></li> <li><a class="reference internal" href="#slots">3.3.2.4. __slots__</a><ul> <li><a class="reference internal" href="#object.__slots__"><code class="docutils literal notranslate">__slots__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#customizing-class-creation">3.3.3. Customizing class creation</a><ul> <li><a class="reference internal" href="#object.__init_subclass__"><code class="docutils literal notranslate">__init_subclass__()</code></a></li> <li><a class="reference internal" href="#object.__set_name__"><code class="docutils literal notranslate">__set_name__()</code></a></li> <li><a class="reference internal" href="#metaclasses">3.3.3.1. Metaclasses</a></li> <li><a class="reference internal" href="#resolving-mro-entries">3.3.3.2. Resolving MRO entries</a><ul> <li><a class="reference internal" href="#object.__mro_entries__"><code class="docutils literal notranslate">__mro_entries__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#determining-the-appropriate-metaclass">3.3.3.3. Determining the appropriate metaclass</a></li> <li><a class="reference internal" href="#preparing-the-class-namespace">3.3.3.4. Preparing the class namespace</a></li> <li><a class="reference internal" href="#executing-the-class-body">3.3.3.5. Executing the class body</a></li> <li><a class="reference internal" href="#creating-the-class-object">3.3.3.6. Creating the class object</a></li> <li><a class="reference internal" href="#uses-for-metaclasses">3.3.3.7. Uses for metaclasses</a></li> </ul> </li> <li><a class="reference internal" href="#customizing-instance-and-subclass-checks">3.3.4. Customizing instance and subclass checks</a><ul> <li><a class="reference internal" href="#type.__instancecheck__"><code class="docutils literal notranslate">__instancecheck__()</code></a></li> <li><a class="reference internal" href="#type.__subclasscheck__"><code class="docutils literal notranslate">__subclasscheck__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-generic-types">3.3.5. Emulating generic types</a><ul> <li><a class="reference internal" href="#object.__class_getitem__"><code class="docutils literal notranslate">__class_getitem__()</code></a></li> <li><a class="reference internal" href="#the-purpose-of-class-getitem">3.3.5.1. The purpose of __class_getitem__</a></li> <li><a class="reference internal" href="#class-getitem-versus-getitem">3.3.5.2. __class_getitem__ versus __getitem__</a></li> </ul> </li> <li><a class="reference internal" href="#emulating-callable-objects">3.3.6. Emulating callable objects</a><ul> <li><a class="reference internal" href="#object.__call__"><code class="docutils literal notranslate">__call__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-container-types">3.3.7. Emulating container types</a><ul> <li><a class="reference internal" href="#object.__len__"><code class="docutils literal notranslate">__len__()</code></a></li> <li><a class="reference internal" href="#object.__length_hint__"><code class="docutils literal notranslate">__length_hint__()</code></a></li> <li><a class="reference internal" href="#object.__getitem__"><code class="docutils literal notranslate">__getitem__()</code></a></li> <li><a class="reference internal" href="#object.__setitem__"><code class="docutils literal notranslate">__setitem__()</code></a></li> <li><a class="reference internal" href="#object.__delitem__"><code class="docutils literal notranslate">__delitem__()</code></a></li> <li><a class="reference internal" href="#object.__missing__"><code class="docutils literal notranslate">__missing__()</code></a></li> <li><a class="reference internal" href="#object.__iter__"><code class="docutils literal notranslate">__iter__()</code></a></li> <li><a class="reference internal" href="#object.__reversed__"><code class="docutils literal notranslate">__reversed__()</code></a></li> <li><a class="reference internal" href="#object.__contains__"><code class="docutils literal notranslate">__contains__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-numeric-types">3.3.8. Emulating numeric types</a><ul> <li><a class="reference internal" href="#object.__add__"><code class="docutils literal notranslate">__add__()</code></a></li> <li><a class="reference internal" href="#object.__sub__"><code class="docutils literal notranslate">__sub__()</code></a></li> <li><a class="reference internal" href="#object.__mul__"><code class="docutils literal notranslate">__mul__()</code></a></li> <li><a class="reference internal" href="#object.__matmul__"><code class="docutils literal notranslate">__matmul__()</code></a></li> <li><a class="reference internal" href="#object.__truediv__"><code class="docutils literal notranslate">__truediv__()</code></a></li> <li><a class="reference internal" href="#object.__floordiv__"><code class="docutils literal notranslate">__floordiv__()</code></a></li> <li><a class="reference internal" href="#object.__mod__"><code class="docutils literal notranslate">__mod__()</code></a></li> <li><a class="reference internal" href="#object.__divmod__"><code class="docutils literal notranslate">__divmod__()</code></a></li> <li><a class="reference internal" href="#object.__pow__"><code class="docutils literal notranslate">__pow__()</code></a></li> <li><a class="reference internal" href="#object.__lshift__"><code class="docutils literal notranslate">__lshift__()</code></a></li> <li><a class="reference internal" href="#object.__rshift__"><code class="docutils literal notranslate">__rshift__()</code></a></li> <li><a class="reference internal" href="#object.__and__"><code class="docutils literal notranslate">__and__()</code></a></li> <li><a class="reference internal" href="#object.__xor__"><code class="docutils literal notranslate">__xor__()</code></a></li> <li><a class="reference internal" href="#object.__or__"><code class="docutils literal notranslate">__or__()</code></a></li> <li><a class="reference internal" href="#object.__radd__"><code class="docutils literal notranslate">__radd__()</code></a></li> <li><a class="reference internal" href="#object.__rsub__"><code class="docutils literal notranslate">__rsub__()</code></a></li> <li><a class="reference internal" href="#object.__rmul__"><code class="docutils literal notranslate">__rmul__()</code></a></li> <li><a class="reference internal" href="#object.__rmatmul__"><code class="docutils literal notranslate">__rmatmul__()</code></a></li> <li><a class="reference internal" href="#object.__rtruediv__"><code class="docutils literal notranslate">__rtruediv__()</code></a></li> <li><a class="reference internal" href="#object.__rfloordiv__"><code class="docutils literal notranslate">__rfloordiv__()</code></a></li> <li><a class="reference internal" href="#object.__rmod__"><code class="docutils literal notranslate">__rmod__()</code></a></li> <li><a class="reference internal" href="#object.__rdivmod__"><code class="docutils literal notranslate">__rdivmod__()</code></a></li> <li><a class="reference internal" href="#object.__rpow__"><code class="docutils literal notranslate">__rpow__()</code></a></li> <li><a class="reference internal" href="#object.__rlshift__"><code class="docutils literal notranslate">__rlshift__()</code></a></li> <li><a class="reference internal" href="#object.__rrshift__"><code class="docutils literal notranslate">__rrshift__()</code></a></li> <li><a class="reference internal" href="#object.__rand__"><code class="docutils literal notranslate">__rand__()</code></a></li> <li><a class="reference internal" href="#object.__rxor__"><code class="docutils literal notranslate">__rxor__()</code></a></li> <li><a class="reference internal" href="#object.__ror__"><code class="docutils literal notranslate">__ror__()</code></a></li> <li><a class="reference internal" href="#object.__iadd__"><code class="docutils literal notranslate">__iadd__()</code></a></li> <li><a class="reference internal" href="#object.__isub__"><code class="docutils literal notranslate">__isub__()</code></a></li> <li><a class="reference internal" href="#object.__imul__"><code class="docutils literal notranslate">__imul__()</code></a></li> <li><a class="reference internal" href="#object.__imatmul__"><code class="docutils literal notranslate">__imatmul__()</code></a></li> <li><a class="reference internal" href="#object.__itruediv__"><code class="docutils literal notranslate">__itruediv__()</code></a></li> <li><a class="reference internal" href="#object.__ifloordiv__"><code class="docutils literal notranslate">__ifloordiv__()</code></a></li> <li><a class="reference internal" href="#object.__imod__"><code class="docutils literal notranslate">__imod__()</code></a></li> <li><a class="reference internal" href="#object.__ipow__"><code class="docutils literal notranslate">__ipow__()</code></a></li> <li><a class="reference internal" href="#object.__ilshift__"><code class="docutils literal notranslate">__ilshift__()</code></a></li> <li><a class="reference internal" href="#object.__irshift__"><code class="docutils literal notranslate">__irshift__()</code></a></li> <li><a class="reference internal" href="#object.__iand__"><code class="docutils literal notranslate">__iand__()</code></a></li> <li><a class="reference internal" href="#object.__ixor__"><code class="docutils literal notranslate">__ixor__()</code></a></li> <li><a class="reference internal" href="#object.__ior__"><code class="docutils literal notranslate">__ior__()</code></a></li> <li><a class="reference internal" href="#object.__neg__"><code class="docutils literal notranslate">__neg__()</code></a></li> <li><a class="reference internal" href="#object.__pos__"><code class="docutils literal notranslate">__pos__()</code></a></li> <li><a class="reference internal" href="#object.__abs__"><code class="docutils literal notranslate">__abs__()</code></a></li> <li><a class="reference internal" href="#object.__invert__"><code class="docutils literal notranslate">__invert__()</code></a></li> <li><a class="reference internal" href="#object.__complex__"><code class="docutils literal notranslate">__complex__()</code></a></li> <li><a class="reference internal" href="#object.__int__"><code class="docutils literal notranslate">__int__()</code></a></li> <li><a class="reference internal" href="#object.__float__"><code class="docutils literal notranslate">__float__()</code></a></li> <li><a class="reference internal" href="#object.__index__"><code class="docutils literal notranslate">__index__()</code></a></li> <li><a class="reference internal" href="#object.__round__"><code class="docutils literal notranslate">__round__()</code></a></li> <li><a class="reference internal" href="#object.__trunc__"><code class="docutils literal notranslate">__trunc__()</code></a></li> <li><a class="reference internal" href="#object.__floor__"><code class="docutils literal notranslate">__floor__()</code></a></li> <li><a class="reference internal" href="#object.__ceil__"><code class="docutils literal notranslate">__ceil__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#with-statement-context-managers">3.3.9. With Statement Context Managers</a><ul> <li><a class="reference internal" href="#object.__enter__"><code class="docutils literal notranslate">__enter__()</code></a></li> <li><a class="reference internal" href="#object.__exit__"><code class="docutils literal notranslate">__exit__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#customizing-positional-arguments-in-class-pattern-matching">3.3.10. Customizing positional arguments in class pattern matching</a><ul> <li><a class="reference internal" href="#object.__match_args__"><code class="docutils literal notranslate">__match_args__</code></a></li> </ul> </li> <li><a class="reference internal" href="#emulating-buffer-types">3.3.11. Emulating buffer types</a><ul> <li><a class="reference internal" href="#object.__buffer__"><code class="docutils literal notranslate">__buffer__()</code></a></li> <li><a class="reference internal" href="#object.__release_buffer__"><code class="docutils literal notranslate">__release_buffer__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-method-lookup">3.3.12. Special method lookup</a></li> </ul> </li> <li><a class="reference internal" href="#coroutines">3.4. Coroutines</a><ul> <li><a class="reference internal" href="#awaitable-objects">3.4.1. Awaitable Objects</a><ul> <li><a class="reference internal" href="#object.__await__"><code class="docutils literal notranslate">__await__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#coroutine-objects">3.4.2. Coroutine Objects</a><ul> <li><a class="reference internal" href="#coroutine.send"><code class="docutils literal notranslate">send()</code></a></li> <li><a class="reference internal" href="#coroutine.throw"><code class="docutils literal notranslate">throw()</code></a></li> <li><a class="reference internal" href="#coroutine.close"><code class="docutils literal notranslate">close()</code></a></li> </ul> </li> <li><a class="reference internal" href="#asynchronous-iterators">3.4.3. Asynchronous Iterators</a><ul> <li><a class="reference internal" href="#object.__aiter__"><code class="docutils literal notranslate">__aiter__()</code></a></li> <li><a class="reference internal" href="#object.__anext__"><code class="docutils literal notranslate">__anext__()</code></a></li> </ul> </li> <li><a class="reference internal" href="#asynchronous-context-managers">3.4.4. Asynchronous Context Managers</a><ul> <li><a class="reference internal" href="#object.__aenter__"><code class="docutils literal notranslate">__aenter__()</code></a></li> <li><a class="reference internal" href="#object.__aexit__"><code class="docutils literal notranslate">__aexit__()</code></a></li> </ul> </li> </ul> </li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="lexical_analysis.html" title="previous chapter">2. Lexical analysis</a> </div> <div> <h4>Next topic</h4> <a href="executionmodel.html" title="next chapter">4. 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