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value="dark">Dark</option> </select> </label> <div> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate">typing</code> — Support for type hints</a><ul> <li><a class="reference internal" href="#specification-for-the-python-type-system">Specification for the Python Type System</a></li> <li><a class="reference internal" href="#type-aliases">Type aliases</a></li> <li><a class="reference internal" href="#newtype">NewType</a></li> <li><a class="reference internal" href="#annotating-callable-objects">Annotating callable objects</a></li> <li><a class="reference internal" href="#generics">Generics</a></li> <li><a class="reference internal" href="#annotating-tuples">Annotating tuples</a></li> <li><a class="reference internal" href="#the-type-of-class-objects">The type of class objects</a></li> <li><a class="reference internal" href="#annotating-generators-and-coroutines">Annotating generators and coroutines</a></li> <li><a class="reference internal" href="#user-defined-generic-types">User-defined generic types</a></li> <li><a class="reference internal" href="#the-any-type">The <code class="xref py py-data docutils literal notranslate">Any</code> type</a></li> <li><a class="reference internal" href="#nominal-vs-structural-subtyping">Nominal vs structural subtyping</a></li> <li><a class="reference internal" href="#module-contents">Module contents</a><ul> <li><a class="reference internal" href="#special-typing-primitives">Special typing primitives</a><ul> <li><a class="reference internal" href="#special-types">Special types</a><ul> <li><a class="reference internal" href="#typing.Any"><code class="docutils literal notranslate">Any</code></a></li> <li><a class="reference internal" href="#typing.AnyStr"><code class="docutils literal notranslate">AnyStr</code></a></li> <li><a class="reference internal" href="#typing.LiteralString"><code class="docutils literal notranslate">LiteralString</code></a></li> <li><a class="reference internal" href="#typing.Never"><code class="docutils literal notranslate">Never</code></a></li> <li><a class="reference internal" href="#typing.NoReturn"><code class="docutils literal notranslate">NoReturn</code></a></li> <li><a class="reference internal" href="#typing.Self"><code class="docutils literal notranslate">Self</code></a></li> <li><a class="reference internal" href="#typing.TypeAlias"><code class="docutils literal notranslate">TypeAlias</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-forms">Special forms</a><ul> <li><a class="reference internal" href="#typing.Union"><code class="docutils literal notranslate">Union</code></a></li> <li><a class="reference internal" href="#typing.Optional"><code class="docutils literal notranslate">Optional</code></a></li> <li><a class="reference internal" href="#typing.Concatenate"><code class="docutils literal notranslate">Concatenate</code></a></li> <li><a class="reference internal" href="#typing.Literal"><code class="docutils literal notranslate">Literal</code></a></li> <li><a class="reference internal" href="#typing.ClassVar"><code class="docutils literal notranslate">ClassVar</code></a></li> <li><a class="reference internal" href="#typing.Final"><code class="docutils literal notranslate">Final</code></a></li> <li><a class="reference internal" href="#typing.Required"><code class="docutils literal notranslate">Required</code></a></li> <li><a class="reference internal" href="#typing.NotRequired"><code class="docutils literal notranslate">NotRequired</code></a></li> <li><a class="reference internal" href="#typing.ReadOnly"><code class="docutils literal notranslate">ReadOnly</code></a></li> <li><a class="reference internal" href="#typing.Annotated"><code class="docutils literal notranslate">Annotated</code></a></li> <li><a class="reference internal" href="#typing.TypeIs"><code class="docutils literal notranslate">TypeIs</code></a></li> <li><a class="reference internal" href="#typing.TypeGuard"><code class="docutils literal notranslate">TypeGuard</code></a></li> <li><a class="reference internal" href="#typing.Unpack"><code class="docutils literal notranslate">Unpack</code></a></li> </ul> </li> <li><a class="reference internal" href="#building-generic-types-and-type-aliases">Building generic types and type aliases</a><ul> <li><a class="reference internal" href="#typing.Generic"><code class="docutils literal notranslate">Generic</code></a></li> <li><a class="reference internal" href="#typing.TypeVar"><code class="docutils literal notranslate">TypeVar</code></a><ul> <li><a class="reference internal" href="#typing.TypeVar.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__covariant__"><code class="docutils literal notranslate">__covariant__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__contravariant__"><code class="docutils literal notranslate">__contravariant__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__infer_variance__"><code class="docutils literal notranslate">__infer_variance__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__bound__"><code class="docutils literal notranslate">__bound__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__constraints__"><code class="docutils literal notranslate">__constraints__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__default__"><code class="docutils literal notranslate">__default__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.has_default"><code class="docutils literal notranslate">has_default()</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.TypeVarTuple"><code class="docutils literal notranslate">TypeVarTuple</code></a><ul> <li><a class="reference internal" href="#typing.TypeVarTuple.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.TypeVarTuple.__default__"><code class="docutils literal notranslate">__default__</code></a></li> <li><a class="reference internal" href="#typing.TypeVarTuple.has_default"><code class="docutils literal notranslate">has_default()</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.ParamSpec"><code class="docutils literal notranslate">ParamSpec</code></a><ul> <li><a class="reference internal" href="#typing.ParamSpec.args"><code class="docutils literal notranslate">args</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.kwargs"><code class="docutils literal notranslate">kwargs</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.__default__"><code class="docutils literal notranslate">__default__</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.has_default"><code class="docutils literal notranslate">has_default()</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.ParamSpecArgs"><code class="docutils literal notranslate">ParamSpecArgs</code></a></li> <li><a class="reference internal" href="#typing.ParamSpecKwargs"><code class="docutils literal notranslate">ParamSpecKwargs</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType"><code class="docutils literal notranslate">TypeAliasType</code></a><ul> <li><a class="reference internal" href="#typing.TypeAliasType.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType.__type_params__"><code class="docutils literal notranslate">__type_params__</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType.__value__"><code class="docutils literal notranslate">__value__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#other-special-directives">Other special directives</a><ul> <li><a class="reference internal" href="#typing.NamedTuple"><code class="docutils literal notranslate">NamedTuple</code></a></li> <li><a class="reference internal" href="#typing.NewType"><code class="docutils literal notranslate">NewType</code></a><ul> <li><a class="reference internal" href="#typing.NewType.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#typing.NewType.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.NewType.__supertype__"><code class="docutils literal notranslate">__supertype__</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.Protocol"><code class="docutils literal notranslate">Protocol</code></a></li> <li><a class="reference internal" href="#typing.runtime_checkable"><code class="docutils literal notranslate">runtime_checkable()</code></a></li> <li><a class="reference internal" href="#typing.TypedDict"><code class="docutils literal notranslate">TypedDict</code></a><ul> <li><a class="reference internal" href="#typing.TypedDict.__total__"><code class="docutils literal notranslate">__total__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__required_keys__"><code class="docutils literal notranslate">__required_keys__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__optional_keys__"><code class="docutils literal notranslate">__optional_keys__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__readonly_keys__"><code class="docutils literal notranslate">__readonly_keys__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__mutable_keys__"><code class="docutils literal notranslate">__mutable_keys__</code></a></li> </ul> </li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#protocols">Protocols</a><ul> <li><a class="reference internal" href="#typing.SupportsAbs"><code class="docutils literal notranslate">SupportsAbs</code></a></li> <li><a class="reference internal" href="#typing.SupportsBytes"><code class="docutils literal notranslate">SupportsBytes</code></a></li> <li><a class="reference internal" href="#typing.SupportsComplex"><code class="docutils literal notranslate">SupportsComplex</code></a></li> <li><a class="reference internal" href="#typing.SupportsFloat"><code class="docutils literal notranslate">SupportsFloat</code></a></li> <li><a class="reference internal" href="#typing.SupportsIndex"><code class="docutils literal notranslate">SupportsIndex</code></a></li> <li><a class="reference internal" href="#typing.SupportsInt"><code class="docutils literal notranslate">SupportsInt</code></a></li> <li><a class="reference internal" href="#typing.SupportsRound"><code class="docutils literal notranslate">SupportsRound</code></a></li> </ul> </li> <li><a class="reference internal" href="#abcs-for-working-with-io">ABCs for working with IO</a><ul> <li><a class="reference internal" href="#typing.IO"><code class="docutils literal notranslate">IO</code></a></li> <li><a class="reference internal" href="#typing.TextIO"><code class="docutils literal notranslate">TextIO</code></a></li> <li><a class="reference internal" href="#typing.BinaryIO"><code class="docutils literal notranslate">BinaryIO</code></a></li> </ul> </li> <li><a class="reference internal" href="#functions-and-decorators">Functions and decorators</a><ul> <li><a class="reference internal" href="#typing.cast"><code class="docutils literal notranslate">cast()</code></a></li> <li><a class="reference internal" href="#typing.assert_type"><code class="docutils literal notranslate">assert_type()</code></a></li> <li><a class="reference internal" href="#typing.assert_never"><code class="docutils literal notranslate">assert_never()</code></a></li> <li><a class="reference internal" href="#typing.reveal_type"><code class="docutils literal notranslate">reveal_type()</code></a></li> <li><a class="reference internal" href="#typing.dataclass_transform"><code class="docutils literal notranslate">dataclass_transform()</code></a></li> <li><a class="reference internal" href="#typing.overload"><code class="docutils literal notranslate">overload()</code></a></li> <li><a class="reference internal" href="#typing.get_overloads"><code class="docutils literal notranslate">get_overloads()</code></a></li> <li><a class="reference internal" href="#typing.clear_overloads"><code class="docutils literal notranslate">clear_overloads()</code></a></li> <li><a class="reference internal" href="#typing.final"><code class="docutils literal notranslate">final()</code></a></li> <li><a class="reference internal" href="#typing.no_type_check"><code class="docutils literal notranslate">no_type_check()</code></a></li> <li><a class="reference internal" href="#typing.no_type_check_decorator"><code class="docutils literal notranslate">no_type_check_decorator()</code></a></li> <li><a class="reference internal" href="#typing.override"><code class="docutils literal notranslate">override()</code></a></li> <li><a class="reference internal" href="#typing.type_check_only"><code class="docutils literal notranslate">type_check_only()</code></a></li> </ul> </li> <li><a class="reference internal" href="#introspection-helpers">Introspection helpers</a><ul> <li><a class="reference internal" href="#typing.get_type_hints"><code class="docutils literal notranslate">get_type_hints()</code></a></li> <li><a class="reference internal" href="#typing.get_origin"><code class="docutils literal notranslate">get_origin()</code></a></li> <li><a class="reference internal" href="#typing.get_args"><code class="docutils literal notranslate">get_args()</code></a></li> <li><a class="reference internal" href="#typing.get_protocol_members"><code class="docutils literal notranslate">get_protocol_members()</code></a></li> <li><a class="reference internal" href="#typing.is_protocol"><code class="docutils literal notranslate">is_protocol()</code></a></li> <li><a class="reference internal" href="#typing.is_typeddict"><code class="docutils literal notranslate">is_typeddict()</code></a></li> <li><a class="reference internal" href="#typing.ForwardRef"><code class="docutils literal notranslate">ForwardRef</code></a></li> <li><a class="reference internal" href="#typing.NoDefault"><code class="docutils literal notranslate">NoDefault</code></a></li> </ul> </li> <li><a class="reference internal" href="#constant">Constant</a><ul> <li><a class="reference internal" href="#typing.TYPE_CHECKING"><code class="docutils literal notranslate">TYPE_CHECKING</code></a></li> </ul> </li> <li><a class="reference internal" href="#deprecated-aliases">Deprecated aliases</a><ul> <li><a class="reference internal" href="#aliases-to-built-in-types">Aliases to built-in types</a><ul> <li><a class="reference internal" href="#typing.Dict"><code class="docutils literal notranslate">Dict</code></a></li> <li><a class="reference internal" href="#typing.List"><code class="docutils literal notranslate">List</code></a></li> <li><a class="reference internal" href="#typing.Set"><code class="docutils literal notranslate">Set</code></a></li> <li><a class="reference internal" href="#typing.FrozenSet"><code class="docutils literal notranslate">FrozenSet</code></a></li> <li><a class="reference internal" href="#typing.Tuple"><code class="docutils literal notranslate">Tuple</code></a></li> <li><a class="reference internal" href="#typing.Type"><code class="docutils literal notranslate">Type</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-types-in-collections">Aliases to types in <code class="xref py py-mod docutils literal notranslate">collections</code></a><ul> <li><a class="reference internal" href="#typing.DefaultDict"><code class="docutils literal notranslate">DefaultDict</code></a></li> <li><a class="reference internal" href="#typing.OrderedDict"><code class="docutils literal notranslate">OrderedDict</code></a></li> <li><a class="reference internal" href="#typing.ChainMap"><code class="docutils literal notranslate">ChainMap</code></a></li> <li><a class="reference internal" href="#typing.Counter"><code class="docutils literal notranslate">Counter</code></a></li> <li><a class="reference internal" href="#typing.Deque"><code class="docutils literal notranslate">Deque</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-other-concrete-types">Aliases to other concrete types</a><ul> <li><a class="reference internal" href="#typing.Pattern"><code class="docutils literal notranslate">Pattern</code></a></li> <li><a class="reference internal" href="#typing.Match"><code class="docutils literal notranslate">Match</code></a></li> <li><a class="reference internal" href="#typing.Text"><code class="docutils literal notranslate">Text</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-container-abcs-in-collections-abc">Aliases to container ABCs in <code class="xref py py-mod docutils literal notranslate">collections.abc</code></a><ul> <li><a class="reference internal" href="#typing.AbstractSet"><code class="docutils literal notranslate">AbstractSet</code></a></li> <li><a class="reference internal" href="#typing.ByteString"><code class="docutils literal notranslate">ByteString</code></a></li> <li><a class="reference internal" href="#typing.Collection"><code class="docutils literal notranslate">Collection</code></a></li> <li><a class="reference internal" href="#typing.Container"><code class="docutils literal notranslate">Container</code></a></li> <li><a class="reference internal" href="#typing.ItemsView"><code class="docutils literal notranslate">ItemsView</code></a></li> <li><a class="reference internal" href="#typing.KeysView"><code class="docutils literal notranslate">KeysView</code></a></li> <li><a class="reference internal" href="#typing.Mapping"><code class="docutils literal notranslate">Mapping</code></a></li> <li><a class="reference internal" href="#typing.MappingView"><code class="docutils literal notranslate">MappingView</code></a></li> <li><a class="reference internal" href="#typing.MutableMapping"><code class="docutils literal notranslate">MutableMapping</code></a></li> <li><a class="reference internal" href="#typing.MutableSequence"><code class="docutils literal notranslate">MutableSequence</code></a></li> <li><a class="reference internal" href="#typing.MutableSet"><code class="docutils literal notranslate">MutableSet</code></a></li> <li><a class="reference internal" href="#typing.Sequence"><code class="docutils literal notranslate">Sequence</code></a></li> <li><a class="reference internal" href="#typing.ValuesView"><code class="docutils literal notranslate">ValuesView</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-asynchronous-abcs-in-collections-abc">Aliases to asynchronous ABCs in <code class="xref py py-mod docutils literal notranslate">collections.abc</code></a><ul> <li><a class="reference internal" href="#typing.Coroutine"><code class="docutils literal notranslate">Coroutine</code></a></li> <li><a class="reference internal" href="#typing.AsyncGenerator"><code class="docutils literal notranslate">AsyncGenerator</code></a></li> <li><a class="reference internal" href="#typing.AsyncIterable"><code class="docutils literal notranslate">AsyncIterable</code></a></li> <li><a class="reference internal" href="#typing.AsyncIterator"><code class="docutils literal notranslate">AsyncIterator</code></a></li> <li><a class="reference internal" href="#typing.Awaitable"><code class="docutils literal notranslate">Awaitable</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-other-abcs-in-collections-abc">Aliases to other ABCs in <code class="xref py py-mod docutils literal notranslate">collections.abc</code></a><ul> <li><a class="reference internal" href="#typing.Iterable"><code class="docutils literal notranslate">Iterable</code></a></li> <li><a class="reference internal" href="#typing.Iterator"><code class="docutils literal notranslate">Iterator</code></a></li> <li><a class="reference internal" href="#typing.Callable"><code class="docutils literal notranslate">Callable</code></a></li> <li><a class="reference internal" href="#typing.Generator"><code class="docutils literal notranslate">Generator</code></a></li> <li><a class="reference internal" href="#typing.Hashable"><code class="docutils literal notranslate">Hashable</code></a></li> <li><a class="reference internal" href="#typing.Reversible"><code class="docutils literal notranslate">Reversible</code></a></li> <li><a class="reference internal" href="#typing.Sized"><code class="docutils literal notranslate">Sized</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-contextlib-abcs">Aliases to <code class="xref py py-mod docutils literal notranslate">contextlib</code> ABCs</a><ul> <li><a class="reference internal" href="#typing.ContextManager"><code class="docutils literal notranslate">ContextManager</code></a></li> <li><a class="reference internal" href="#typing.AsyncContextManager"><code class="docutils literal notranslate">AsyncContextManager</code></a></li> </ul> </li> </ul> </li> </ul> </li> <li><a class="reference internal" 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Module Index" >modules</a> |</li> <li class="right" > <a href="pydoc.html" title="pydoc — Documentation generator and online help system" accesskey="N">next</a> |</li> <li class="right" > <a href="development.html" title="Development Tools" 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" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="development.html" accesskey="U">Development Tools</a> »</li> <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate">typing</code> — Support for type hints</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="typing-support-for-type-hints"> <h1><a class="reference internal" href="#module-typing" title="typing: Support for type hints (see :pep:`484`)."><code class="xref py py-mod docutils literal notranslate">typing</code></a> — Support for type hints<a class="headerlink" href="#typing-support-for-type-hints" title="Link to this heading">¶</a></h1> <div class="versionadded" id="module-typing"> Added in version 3.5. </div> Source code: <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.13/Lib/typing.py">Lib/typing.py</a> <div class="admonition note"> Note The Python runtime does not enforce function and variable type annotations. They can be used by third party tools such as <a class="reference internal" href="../glossary.html#term-static-type-checker">type checkers</a>, IDEs, linters, etc. </div> <hr class="docutils" /> This module provides runtime support for type hints. Consider the function below: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def surface_area_of_cube(edge_length: float) -> str: return f"The surface area of the cube is {6 * edge_length ** 2}." </pre></div> </div> The function <code class="docutils literal notranslate">surface_area_of_cube</code> takes an argument expected to be an instance of <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a>, as indicated by the <a class="reference internal" href="../glossary.html#term-type-hint">type hint</a> <code class="docutils literal notranslate">edge_length: float</code>. The function is expected to return an instance of <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, as indicated by the <code class="docutils literal notranslate">-> str</code> hint. While type hints can be simple classes like <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a> or <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, they can also be more complex. The <a class="reference internal" href="#module-typing" title="typing: Support for type hints (see :pep:`484`)."><code class="xref py py-mod docutils literal notranslate">typing</code></a> module provides a vocabulary of more advanced type hints. New features are frequently added to the <code class="docutils literal notranslate">typing</code> module. The <a class="extlink-pypi reference external" href="https://pypi.org/project/typing_extensions/">typing_extensions</a> package provides backports of these new features to older versions of Python. <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="reference external" href="https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html">“Typing cheat sheet”</a></dt><dd>A quick overview of type hints (hosted at the mypy docs) </dd> <dt>“Type System Reference” section of <a class="reference external" href="https://mypy.readthedocs.io/en/stable/index.html">the mypy docs</a></dt><dd>The Python typing system is standardised via PEPs, so this reference should broadly apply to most Python type checkers. (Some parts may still be specific to mypy.) </dd> <dt><a class="reference external" href="https://typing.readthedocs.io/en/latest/">“Static Typing with Python”</a></dt><dd>Type-checker-agnostic documentation written by the community detailing type system features, useful typing related tools and typing best practices. </dd> </dl> </div> <section id="specification-for-the-python-type-system"> <h2>Specification for the Python Type System<a class="headerlink" href="#specification-for-the-python-type-system" title="Link to this heading">¶</a></h2> The canonical, up-to-date specification of the Python type system can be found at <a class="reference external" href="https://typing.readthedocs.io/en/latest/spec/index.html">“Specification for the Python type system”</a>. </section> <section id="type-aliases"> <h2>Type aliases<a class="headerlink" href="#type-aliases" title="Link to this heading">¶</a></h2> A type alias is defined using the <a class="reference internal" href="../reference/simple_stmts.html#type"><code class="xref std std-keyword docutils literal notranslate">type</code></a> statement, which creates an instance of <a class="reference internal" href="#typing.TypeAliasType" title="typing.TypeAliasType"><code class="xref py py-class docutils literal notranslate">TypeAliasType</code></a>. In this example, <code class="docutils literal notranslate">Vector</code> and <code class="docutils literal notranslate">list[float]</code> will be treated equivalently by static type checkers: <div class="highlight-python3 notranslate"><div class="highlight"><pre>type Vector = list[float] def scale(scalar: float, vector: Vector) -> Vector: return [scalar * num for num in vector] # passes type checking; a list of floats qualifies as a Vector. new_vector = scale(2.0, [1.0, -4.2, 5.4]) </pre></div> </div> Type aliases are useful for simplifying complex type signatures. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Sequence type ConnectionOptions = dict[str, str] type Address = tuple[str, int] type Server = tuple[Address, ConnectionOptions] def broadcast_message(message: str, servers: Sequence[Server]) -> None: ... # The static type checker will treat the previous type signature as # being exactly equivalent to this one. def broadcast_message( message: str, servers: Sequence[tuple[tuple[str, int], dict[str, str]]] ) -> None: ... </pre></div> </div> The <a class="reference internal" href="../reference/simple_stmts.html#type"><code class="xref std std-keyword docutils literal notranslate">type</code></a> statement is new in Python 3.12. For backwards compatibility, type aliases can also be created through simple assignment: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Vector = list[float] </pre></div> </div> Or marked with <a class="reference internal" href="#typing.TypeAlias" title="typing.TypeAlias"><code class="xref py py-data docutils literal notranslate">TypeAlias</code></a> to make it explicit that this is a type alias, not a normal variable assignment: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypeAlias Vector: TypeAlias = list[float] </pre></div> </div> </section> <section id="newtype"> <h2>NewType<a class="headerlink" href="#newtype" title="Link to this heading">¶</a></h2> Use the <a class="reference internal" href="#typing.NewType" title="typing.NewType"><code class="xref py py-class docutils literal notranslate">NewType</code></a> helper to create distinct types: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import NewType UserId = NewType('UserId', int) some_id = UserId(524313) </pre></div> </div> The static type checker will treat the new type as if it were a subclass of the original type. This is useful in helping catch logical errors: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def get_user_name(user_id: UserId) -> str: ... # passes type checking user_a = get_user_name(UserId(42351)) # fails type checking; an int is not a UserId user_b = get_user_name(-1) </pre></div> </div> You may still perform all <code class="docutils literal notranslate">int</code> operations on a variable of type <code class="docutils literal notranslate">UserId</code>, but the result will always be of type <code class="docutils literal notranslate">int</code>. This lets you pass in a <code class="docutils literal notranslate">UserId</code> wherever an <code class="docutils literal notranslate">int</code> might be expected, but will prevent you from accidentally creating a <code class="docutils literal notranslate">UserId</code> in an invalid way: <div class="highlight-python3 notranslate"><div class="highlight"><pre># 'output' is of type 'int', not 'UserId' output = UserId(23413) + UserId(54341) </pre></div> </div> Note that these checks are enforced only by the static type checker. At runtime, the statement <code class="docutils literal notranslate">Derived = NewType('Derived', Base)</code> will make <code class="docutils literal notranslate">Derived</code> a callable that immediately returns whatever parameter you pass it. That means the expression <code class="docutils literal notranslate">Derived(some_value)</code> does not create a new class or introduce much overhead beyond that of a regular function call. More precisely, the expression <code class="docutils literal notranslate">some_value is Derived(some_value)</code> is always true at runtime. It is invalid to create a subtype of <code class="docutils literal notranslate">Derived</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import NewType UserId = NewType('UserId', int) # Fails at runtime and does not pass type checking class AdminUserId(UserId): pass </pre></div> </div> However, it is possible to create a <a class="reference internal" href="#typing.NewType" title="typing.NewType"><code class="xref py py-class docutils literal notranslate">NewType</code></a> based on a ‘derived’ <code class="docutils literal notranslate">NewType</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import NewType UserId = NewType('UserId', int) ProUserId = NewType('ProUserId', UserId) </pre></div> </div> and typechecking for <code class="docutils literal notranslate">ProUserId</code> will work as expected. See <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> for more details. <div class="admonition note"> Note Recall that the use of a type alias declares two types to be equivalent to one another. Doing <code class="docutils literal notranslate">type Alias = Original</code> will make the static type checker treat <code class="docutils literal notranslate">Alias</code> as being exactly equivalent to <code class="docutils literal notranslate">Original</code> in all cases. This is useful when you want to simplify complex type signatures. In contrast, <code class="docutils literal notranslate">NewType</code> declares one type to be a subtype of another. Doing <code class="docutils literal notranslate">Derived = NewType('Derived', Original)</code> will make the static type checker treat <code class="docutils literal notranslate">Derived</code> as a subclass of <code class="docutils literal notranslate">Original</code>, which means a value of type <code class="docutils literal notranslate">Original</code> cannot be used in places where a value of type <code class="docutils literal notranslate">Derived</code> is expected. This is useful when you want to prevent logic errors with minimal runtime cost. </div> <div class="versionadded"> Added in version 3.5.2. </div> <div class="versionchanged"> Changed in version 3.10: <code class="docutils literal notranslate">NewType</code> is now a class rather than a function. As a result, there is some additional runtime cost when calling <code class="docutils literal notranslate">NewType</code> over a regular function. </div> <div class="versionchanged"> Changed in version 3.11: The performance of calling <code class="docutils literal notranslate">NewType</code> has been restored to its level in Python 3.9. </div> </section> <section id="annotating-callable-objects"> <h2>Annotating callable objects<a class="headerlink" href="#annotating-callable-objects" title="Link to this heading">¶</a></h2> Functions – or other <a class="reference internal" href="../glossary.html#term-callable">callable</a> objects – can be annotated using <a class="reference internal" href="collections.abc.html#collections.abc.Callable" title="collections.abc.Callable"><code class="xref py py-class docutils literal notranslate">collections.abc.Callable</code></a> or deprecated <a class="reference internal" href="#typing.Callable" title="typing.Callable"><code class="xref py py-data docutils literal notranslate">typing.Callable</code></a>. <code class="docutils literal notranslate">Callable[[int], str]</code> signifies a function that takes a single parameter of type <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> and returns a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>. For example: <div class="highlight-python notranslate"><div class="highlight"><pre>from collections.abc import Callable, Awaitable def feeder(get_next_item: Callable[[], str]) -> None: ... # Body def async_query(on_success: Callable[[int], None], on_error: Callable[[int, Exception], None]) -> None: ... # Body async def on_update(value: str) -> None: ... # Body callback: Callable[[str], Awaitable[None]] = on_update </pre></div> </div> The subscription syntax must always be used with exactly two values: the argument list and the return type. The argument list must be a list of types, a <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a>, <a class="reference internal" href="#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-data docutils literal notranslate">Concatenate</code></a>, or an ellipsis. The return type must be a single type. If a literal ellipsis <code class="docutils literal notranslate">...</code> is given as the argument list, it indicates that a callable with any arbitrary parameter list would be acceptable: <div class="highlight-python notranslate"><div class="highlight"><pre>def concat(x: str, y: str) -> str: return x + y x: Callable[..., str] x = str # OK x = concat # Also OK </pre></div> </div> <code class="docutils literal notranslate">Callable</code> cannot express complex signatures such as functions that take a variadic number of arguments, <a class="reference internal" href="#overload">overloaded functions</a>, or functions that have keyword-only parameters. However, these signatures can be expressed by defining a <a class="reference internal" href="#typing.Protocol" title="typing.Protocol"><code class="xref py py-class docutils literal notranslate">Protocol</code></a> class with a <a class="reference internal" href="../reference/datamodel.html#object.__call__" title="object.__call__"><code class="xref py py-meth docutils literal notranslate">__call__()</code></a> method: <div class="highlight-python notranslate"><div class="highlight"><pre>from collections.abc import Iterable from typing import Protocol class Combiner(Protocol): def __call__(self, *vals: bytes, maxlen: int | None = None) -> list[bytes]: ... def batch_proc(data: Iterable[bytes], cb_results: Combiner) -> bytes: for item in data: ... def good_cb(*vals: bytes, maxlen: int | None = None) -> list[bytes]: ... def bad_cb(*vals: bytes, maxitems: int | None) -> list[bytes]: ... batch_proc([], good_cb) # OK batch_proc([], bad_cb) # Error! Argument 2 has incompatible type because of # different name and kind in the callback </pre></div> </div> Callables which take other callables as arguments may indicate that their parameter types are dependent on each other using <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a>. Additionally, if that callable adds or removes arguments from other callables, the <a class="reference internal" href="#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-data docutils literal notranslate">Concatenate</code></a> operator may be used. They take the form <code class="docutils literal notranslate">Callable[ParamSpecVariable, ReturnType]</code> and <code class="docutils literal notranslate">Callable[Concatenate[Arg1Type, Arg2Type, ..., ParamSpecVariable], ReturnType]</code> respectively. <div class="versionchanged"> Changed in version 3.10: <code class="docutils literal notranslate">Callable</code> now supports <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> and <a class="reference internal" href="#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-data docutils literal notranslate">Concatenate</code></a>. See <a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a> for more details. </div> <div class="admonition seealso"> See also The documentation for <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> and <a class="reference internal" href="#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-class docutils literal notranslate">Concatenate</code></a> provides examples of usage in <code class="docutils literal notranslate">Callable</code>. </div> </section> <section id="generics"> <h2>Generics<a class="headerlink" href="#generics" title="Link to this heading">¶</a></h2> Since type information about objects kept in containers cannot be statically inferred in a generic way, many container classes in the standard library support subscription to denote the expected types of container elements. <div class="highlight-python notranslate"><div class="highlight"><pre>from collections.abc import Mapping, Sequence class Employee: ... # Sequence[Employee] indicates that all elements in the sequence # must be instances of "Employee". # Mapping[str, str] indicates that all keys and all values in the mapping # must be strings. def notify_by_email(employees: Sequence[Employee], overrides: Mapping[str, str]) -> None: ... </pre></div> </div> Generic functions and classes can be parameterized by using <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter syntax</a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Sequence def first[T](l: Sequence[T]) -> T: # Function is generic over the TypeVar "T" return l[0] </pre></div> </div> Or by using the <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal notranslate">TypeVar</code></a> factory directly: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Sequence from typing import TypeVar U = TypeVar('U') # Declare type variable "U" def second(l: Sequence[U]) -> U: # Function is generic over the TypeVar "U" return l[1] </pre></div> </div> <div class="versionchanged"> Changed in version 3.12: Syntactic support for generics is new in Python 3.12. </div> </section> <section id="annotating-tuples"> <h2>Annotating tuples<a class="headerlink" href="#annotating-tuples" title="Link to this heading">¶</a></h2> For most containers in Python, the typing system assumes that all elements in the container will be of the same type. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Mapping # Type checker will infer that all elements in ``x`` are meant to be ints x: list[int] = [] # Type checker error: ``list`` only accepts a single type argument: y: list[int, str] = [1, 'foo'] # Type checker will infer that all keys in ``z`` are meant to be strings, # and that all values in ``z`` are meant to be either strings or ints z: Mapping[str, str | int] = {} </pre></div> </div> <a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a> only accepts one type argument, so a type checker would emit an error on the <code class="docutils literal notranslate">y</code> assignment above. Similarly, <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate">Mapping</code></a> only accepts two type arguments: the first indicates the type of the keys, and the second indicates the type of the values. Unlike most other Python containers, however, it is common in idiomatic Python code for tuples to have elements which are not all of the same type. For this reason, tuples are special-cased in Python’s typing system. <a class="reference internal" href="stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> accepts any number of type arguments: <div class="highlight-python3 notranslate"><div class="highlight"><pre># OK: ``x`` is assigned to a tuple of length 1 where the sole element is an int x: tuple[int] = (5,) # OK: ``y`` is assigned to a tuple of length 2; # element 1 is an int, element 2 is a str y: tuple[int, str] = (5, "foo") # Error: the type annotation indicates a tuple of length 1, # but ``z`` has been assigned to a tuple of length 3 z: tuple[int] = (1, 2, 3) </pre></div> </div> To denote a tuple which could be of any length, and in which all elements are of the same type <code class="docutils literal notranslate">T</code>, use <code class="docutils literal notranslate">tuple[T, ...]</code>. To denote an empty tuple, use <code class="docutils literal notranslate">tuple[()]</code>. Using plain <code class="docutils literal notranslate">tuple</code> as an annotation is equivalent to using <code class="docutils literal notranslate">tuple[Any, ...]</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>x: tuple[int, ...] = (1, 2) # These reassignments are OK: ``tuple[int, ...]`` indicates x can be of any length x = (1, 2, 3) x = () # This reassignment is an error: all elements in ``x`` must be ints x = ("foo", "bar") # ``y`` can only ever be assigned to an empty tuple y: tuple[()] = () z: tuple = ("foo", "bar") # These reassignments are OK: plain ``tuple`` is equivalent to ``tuple[Any, ...]`` z = (1, 2, 3) z = () </pre></div> </div> </section> <section id="the-type-of-class-objects"> <h2>The type of class objects<a class="headerlink" href="#the-type-of-class-objects" title="Link to this heading">¶</a></h2> A variable annotated with <code class="docutils literal notranslate">C</code> may accept a value of type <code class="docutils literal notranslate">C</code>. In contrast, a variable annotated with <code class="docutils literal notranslate">type[C]</code> (or deprecated <a class="reference internal" href="#typing.Type" title="typing.Type"><code class="xref py py-class docutils literal notranslate">typing.Type[C]</code></a>) may accept values that are classes themselves – specifically, it will accept the class object of <code class="docutils literal notranslate">C</code>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>a = 3 # Has type ``int`` b = int # Has type ``type[int]`` c = type(a) # Also has type ``type[int]`` </pre></div> </div> Note that <code class="docutils literal notranslate">type[C]</code> is covariant: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class User: ... class ProUser(User): ... class TeamUser(User): ... def make_new_user(user_class: type[User]) -> User: # ... return user_class() make_new_user(User) # OK make_new_user(ProUser) # Also OK: ``type[ProUser]`` is a subtype of ``type[User]`` make_new_user(TeamUser) # Still fine make_new_user(User()) # Error: expected ``type[User]`` but got ``User`` make_new_user(int) # Error: ``type[int]`` is not a subtype of ``type[User]`` </pre></div> </div> The only legal parameters for <a class="reference internal" href="functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a> are classes, <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>, <a class="reference internal" href="#generics">type variables</a>, and unions of any of these types. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def new_non_team_user(user_class: type[BasicUser | ProUser]): ... new_non_team_user(BasicUser) # OK new_non_team_user(ProUser) # OK new_non_team_user(TeamUser) # Error: ``type[TeamUser]`` is not a subtype # of ``type[BasicUser | ProUser]`` new_non_team_user(User) # Also an error </pre></div> </div> <code class="docutils literal notranslate">type[Any]</code> is equivalent to <a class="reference internal" href="functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a>, which is the root of Python’s <a class="reference internal" href="../reference/datamodel.html#metaclasses">metaclass hierarchy</a>. </section> <section id="annotating-generators-and-coroutines"> <h2>Annotating generators and coroutines<a class="headerlink" href="#annotating-generators-and-coroutines" title="Link to this heading">¶</a></h2> A generator can be annotated using the generic type <a class="reference internal" href="collections.abc.html#collections.abc.Generator" title="collections.abc.Generator"><code class="xref py py-class docutils literal notranslate">Generator[YieldType, SendType, ReturnType]</code></a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def echo_round() -> Generator[int, float, str]: sent = yield 0 while sent >= 0: sent = yield round(sent) return 'Done' </pre></div> </div> Note that unlike many other generic classes in the standard library, the <code class="docutils literal notranslate">SendType</code> of <a class="reference internal" href="collections.abc.html#collections.abc.Generator" title="collections.abc.Generator"><code class="xref py py-class docutils literal notranslate">Generator</code></a> behaves contravariantly, not covariantly or invariantly. The <code class="docutils literal notranslate">SendType</code> and <code class="docutils literal notranslate">ReturnType</code> parameters default to <code class="xref py py-const docutils literal notranslate">None</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def infinite_stream(start: int) -> Generator[int]: while True: yield start start += 1 </pre></div> </div> It is also possible to set these types explicitly: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def infinite_stream(start: int) -> Generator[int, None, None]: while True: yield start start += 1 </pre></div> </div> Simple generators that only ever yield values can also be annotated as having a return type of either <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal notranslate">Iterable[YieldType]</code></a> or <a class="reference internal" href="collections.abc.html#collections.abc.Iterator" title="collections.abc.Iterator"><code class="xref py py-class docutils literal notranslate">Iterator[YieldType]</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def infinite_stream(start: int) -> Iterator[int]: while True: yield start start += 1 </pre></div> </div> Async generators are handled in a similar fashion, but don’t expect a <code class="docutils literal notranslate">ReturnType</code> type argument (<a class="reference internal" href="collections.abc.html#collections.abc.AsyncGenerator" title="collections.abc.AsyncGenerator"><code class="xref py py-class docutils literal notranslate">AsyncGenerator[YieldType, SendType]</code></a>). The <code class="docutils literal notranslate">SendType</code> argument defaults to <code class="xref py py-const docutils literal notranslate">None</code>, so the following definitions are equivalent: <div class="highlight-python3 notranslate"><div class="highlight"><pre>async def infinite_stream(start: int) -> AsyncGenerator[int]: while True: yield start start = await increment(start) async def infinite_stream(start: int) -> AsyncGenerator[int, None]: while True: yield start start = await increment(start) </pre></div> </div> As in the synchronous case, <a class="reference internal" href="collections.abc.html#collections.abc.AsyncIterable" title="collections.abc.AsyncIterable"><code class="xref py py-class docutils literal notranslate">AsyncIterable[YieldType]</code></a> and <a class="reference internal" href="collections.abc.html#collections.abc.AsyncIterator" title="collections.abc.AsyncIterator"><code class="xref py py-class docutils literal notranslate">AsyncIterator[YieldType]</code></a> are available as well: <div class="highlight-python3 notranslate"><div class="highlight"><pre>async def infinite_stream(start: int) -> AsyncIterator[int]: while True: yield start start = await increment(start) </pre></div> </div> Coroutines can be annotated using <a class="reference internal" href="collections.abc.html#collections.abc.Coroutine" title="collections.abc.Coroutine"><code class="xref py py-class docutils literal notranslate">Coroutine[YieldType, SendType, ReturnType]</code></a>. Generic arguments correspond to those of <a class="reference internal" href="collections.abc.html#collections.abc.Generator" title="collections.abc.Generator"><code class="xref py py-class docutils literal notranslate">Generator</code></a>, for example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Coroutine c: Coroutine[list[str], str, int] # Some coroutine defined elsewhere x = c.send('hi') # Inferred type of 'x' is list[str] async def bar() -> None: y = await c # Inferred type of 'y' is int </pre></div> </div> </section> <section id="user-defined-generic-types"> <h2>User-defined generic types<a class="headerlink" href="#user-defined-generic-types" title="Link to this heading">¶</a></h2> A user-defined class can be defined as a generic class. <div class="highlight-python3 notranslate"><div class="highlight"><pre>from logging import Logger class LoggedVar[T]: def __init__(self, value: T, name: str, logger: Logger) -> None: self.name = name self.logger = logger self.value = value def set(self, new: T) -> None: self.log('Set ' + repr(self.value)) self.value = new def get(self) -> T: self.log('Get ' + repr(self.value)) return self.value def log(self, message: str) -> None: self.logger.info('%s: %s', self.name, message) </pre></div> </div> This syntax indicates that the class <code class="docutils literal notranslate">LoggedVar</code> is parameterised around a single <a class="reference internal" href="#typevar">type variable</a> <code class="docutils literal notranslate">T</code> . This also makes <code class="docutils literal notranslate">T</code> valid as a type within the class body. Generic classes implicitly inherit from <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a>. For compatibility with Python 3.11 and lower, it is also possible to inherit explicitly from <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> to indicate a generic class: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypeVar, Generic T = TypeVar('T') class LoggedVar(Generic[T]): ... </pre></div> </div> Generic classes have <a class="reference internal" href="../reference/datamodel.html#object.__class_getitem__" title="object.__class_getitem__"><code class="xref py py-meth docutils literal notranslate">__class_getitem__()</code></a> methods, meaning they can be parameterised at runtime (e.g. <code class="docutils literal notranslate">LoggedVar[int]</code> below): <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Iterable def zero_all_vars(vars: Iterable[LoggedVar[int]]) -> None: for var in vars: var.set(0) </pre></div> </div> A generic type can have any number of type variables. All varieties of <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal notranslate">TypeVar</code></a> are permissible as parameters for a generic type: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypeVar, Generic, Sequence class WeirdTrio[T, B: Sequence[bytes], S: (int, str)]: ... OldT = TypeVar('OldT', contravariant=True) OldB = TypeVar('OldB', bound=Sequence[bytes], covariant=True) OldS = TypeVar('OldS', int, str) class OldWeirdTrio(Generic[OldT, OldB, OldS]): ... </pre></div> </div> Each type variable argument to <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> must be distinct. This is thus invalid: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypeVar, Generic ... class Pair[M, M]: # SyntaxError ... T = TypeVar('T') class Pair(Generic[T, T]): # INVALID ... </pre></div> </div> Generic classes can also inherit from other classes: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Sized class LinkedList[T](Sized): ... </pre></div> </div> When inheriting from generic classes, some type parameters could be fixed: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Mapping class MyDict[T](Mapping[str, T]): ... </pre></div> </div> In this case <code class="docutils literal notranslate">MyDict</code> has a single parameter, <code class="docutils literal notranslate">T</code>. Using a generic class without specifying type parameters assumes <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> for each position. In the following example, <code class="docutils literal notranslate">MyIterable</code> is not generic but implicitly inherits from <code class="docutils literal notranslate">Iterable[Any]</code>: <div class="highlight-python notranslate"><div class="highlight"><pre>from collections.abc import Iterable class MyIterable(Iterable): # Same as Iterable[Any] ... </pre></div> </div> User-defined generic type aliases are also supported. Examples: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Iterable type Response[S] = Iterable[S] | int # Return type here is same as Iterable[str] | int def response(query: str) -> Response[str]: ... type Vec[T] = Iterable[tuple[T, T]] def inproduct[T: (int, float, complex)](v: Vec[T]) -> T: # Same as Iterable[tuple[T, T]] return sum(x*y for x, y in v) </pre></div> </div> For backward compatibility, generic type aliases can also be created through a simple assignment: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Iterable from typing import TypeVar S = TypeVar("S") Response = Iterable[S] | int </pre></div> </div> <div class="versionchanged"> Changed in version 3.7: <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> no longer has a custom metaclass. </div> <div class="versionchanged"> Changed in version 3.12: Syntactic support for generics and type aliases is new in version 3.12. Previously, generic classes had to explicitly inherit from <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> or contain a type variable in one of their bases. </div> User-defined generics for parameter expressions are also supported via parameter specification variables in the form <code class="docutils literal notranslate">[**P]</code>. The behavior is consistent with type variables’ described above as parameter specification variables are treated by the typing module as a specialized type variable. The one exception to this is that a list of types can be used to substitute a <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class Z[T, **P]: ... # T is a TypeVar; P is a ParamSpec ... >>> Z[int, [dict, float]] __main__.Z[int, [dict, float]] </pre></div> </div> Classes generic over a <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> can also be created using explicit inheritance from <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a>. In this case, <code class="docutils literal notranslate">**</code> is not used: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import ParamSpec, Generic P = ParamSpec('P') class Z(Generic[P]): ... </pre></div> </div> Another difference between <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal notranslate">TypeVar</code></a> and <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> is that a generic with only one parameter specification variable will accept parameter lists in the forms <code class="docutils literal notranslate">X[[Type1, Type2, ...]]</code> and also <code class="docutils literal notranslate">X[Type1, Type2, ...]</code> for aesthetic reasons. Internally, the latter is converted to the former, so the following are equivalent: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class X[**P]: ... ... >>> X[int, str] __main__.X[[int, str]] >>> X[[int, str]] __main__.X[[int, str]] </pre></div> </div> Note that generics with <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> may not have correct <code class="docutils literal notranslate">__parameters__</code> after substitution in some cases because they are intended primarily for static type checking. <div class="versionchanged"> Changed in version 3.10: <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> can now be parameterized over parameter expressions. See <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> and <a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a> for more details. </div> A user-defined generic class can have ABCs as base classes without a metaclass conflict. Generic metaclasses are not supported. The outcome of parameterizing generics is cached, and most types in the typing module are <a class="reference internal" href="../glossary.html#term-hashable">hashable</a> and comparable for equality. </section> <section id="the-any-type"> <h2>The <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> type<a class="headerlink" href="#the-any-type" title="Link to this heading">¶</a></h2> A special kind of type is <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>. A static type checker will treat every type as being compatible with <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> and <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> as being compatible with every type. This means that it is possible to perform any operation or method call on a value of type <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> and assign it to any variable: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import Any a: Any = None a = [] # OK a = 2 # OK s: str = '' s = a # OK def foo(item: Any) -> int: # Passes type checking; 'item' could be any type, # and that type might have a 'bar' method item.bar() ... </pre></div> </div> Notice that no type checking is performed when assigning a value of type <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> to a more precise type. For example, the static type checker did not report an error when assigning <code class="docutils literal notranslate">a</code> to <code class="docutils literal notranslate">s</code> even though <code class="docutils literal notranslate">s</code> was declared to be of type <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> and receives an <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> value at runtime! Furthermore, all functions without a return type or parameter types will implicitly default to using <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def legacy_parser(text): ... return data # A static type checker will treat the above # as having the same signature as: def legacy_parser(text: Any) -> Any: ... return data </pre></div> </div> This behavior allows <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> to be used as an escape hatch when you need to mix dynamically and statically typed code. Contrast the behavior of <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> with the behavior of <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a>. Similar to <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>, every type is a subtype of <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a>. However, unlike <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>, the reverse is not true: <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> is not a subtype of every other type. That means when the type of a value is <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a>, a type checker will reject almost all operations on it, and assigning it to a variable (or using it as a return value) of a more specialized type is a type error. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def hash_a(item: object) -> int: # Fails type checking; an object does not have a 'magic' method. item.magic() ... def hash_b(item: Any) -> int: # Passes type checking item.magic() ... # Passes type checking, since ints and strs are subclasses of object hash_a(42) hash_a("foo") # Passes type checking, since Any is compatible with all types hash_b(42) hash_b("foo") </pre></div> </div> Use <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> to indicate that a value could be any type in a typesafe manner. Use <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> to indicate that a value is dynamically typed. </section> <section id="nominal-vs-structural-subtyping"> <h2>Nominal vs structural subtyping<a class="headerlink" href="#nominal-vs-structural-subtyping" title="Link to this heading">¶</a></h2> Initially <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> defined the Python static type system as using nominal subtyping. This means that a class <code class="docutils literal notranslate">A</code> is allowed where a class <code class="docutils literal notranslate">B</code> is expected if and only if <code class="docutils literal notranslate">A</code> is a subclass of <code class="docutils literal notranslate">B</code>. This requirement previously also applied to abstract base classes, such as <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal notranslate">Iterable</code></a>. The problem with this approach is that a class had to be explicitly marked to support them, which is unpythonic and unlike what one would normally do in idiomatic dynamically typed Python code. For example, this conforms to <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Sized, Iterable, Iterator class Bucket(Sized, Iterable[int]): ... def __len__(self) -> int: ... def __iter__(self) -> Iterator[int]: ... </pre></div> </div> <a class="pep reference external" href="https://peps.python.org/pep-0544/">PEP 544</a> allows to solve this problem by allowing users to write the above code without explicit base classes in the class definition, allowing <code class="docutils literal notranslate">Bucket</code> to be implicitly considered a subtype of both <code class="docutils literal notranslate">Sized</code> and <code class="docutils literal notranslate">Iterable[int]</code> by static type checkers. This is known as structural subtyping (or static duck-typing): <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Iterator, Iterable class Bucket: # Note: no base classes ... def __len__(self) -> int: ... def __iter__(self) -> Iterator[int]: ... def collect(items: Iterable[int]) -> int: ... result = collect(Bucket()) # Passes type check </pre></div> </div> Moreover, by subclassing a special class <a class="reference internal" href="#typing.Protocol" title="typing.Protocol"><code class="xref py py-class docutils literal notranslate">Protocol</code></a>, a user can define new custom protocols to fully enjoy structural subtyping (see examples below). </section> <section id="module-contents"> <h2>Module contents<a class="headerlink" href="#module-contents" title="Link to this heading">¶</a></h2> The <code class="docutils literal notranslate">typing</code> module defines the following classes, functions and decorators. <section id="special-typing-primitives"> <h3>Special typing primitives<a class="headerlink" href="#special-typing-primitives" title="Link to this heading">¶</a></h3> <section id="special-types"> <h4>Special types<a class="headerlink" href="#special-types" title="Link to this heading">¶</a></h4> These can be used as types in annotations. They do not support subscription using <code class="docutils literal notranslate">[]</code>. <dl class="py data"> <dt class="sig sig-object py" id="typing.Any"> typing.Any<a class="headerlink" href="#typing.Any" title="Link to this definition">¶</a></dt> <dd>Special type indicating an unconstrained type. <ul class="simple"> <li>Every type is compatible with <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>.</li> <li><a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> is compatible with every type.</li> </ul> <div class="versionchanged"> Changed in version 3.11: <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a> can now be used as a base class. This can be useful for avoiding type checker errors with classes that can duck type anywhere or are highly dynamic. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.AnyStr"> typing.AnyStr<a class="headerlink" href="#typing.AnyStr" title="Link to this definition">¶</a></dt> <dd>A <a class="reference internal" href="#typing-constrained-typevar">constrained type variable</a>. Definition: <div class="highlight-python3 notranslate"><div class="highlight"><pre>AnyStr = TypeVar('AnyStr', str, bytes) </pre></div> </div> <code class="docutils literal notranslate">AnyStr</code> is meant to be used for functions that may accept <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> or <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> arguments but cannot allow the two to mix. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def concat(a: AnyStr, b: AnyStr) -> AnyStr: return a + b concat("foo", "bar") # OK, output has type 'str' concat(b"foo", b"bar") # OK, output has type 'bytes' concat("foo", b"bar") # Error, cannot mix str and bytes </pre></div> </div> Note that, despite its name, <code class="docutils literal notranslate">AnyStr</code> has nothing to do with the <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-class docutils literal notranslate">Any</code></a> type, nor does it mean “any string”. In particular, <code class="docutils literal notranslate">AnyStr</code> and <code class="docutils literal notranslate">str | bytes</code> are different from each other and have different use cases: <div class="highlight-python3 notranslate"><div class="highlight"><pre># Invalid use of AnyStr: # The type variable is used only once in the function signature, # so cannot be "solved" by the type checker def greet_bad(cond: bool) -> AnyStr: return "hi there!" if cond else b"greetings!" # The better way of annotating this function: def greet_proper(cond: bool) -> str | bytes: return "hi there!" if cond else b"greetings!" </pre></div> </div> <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.18: Deprecated in favor of the new <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter syntax</a>. Use <code class="docutils literal notranslate">class A[T: (str, bytes)]: ...</code> instead of importing <code class="docutils literal notranslate">AnyStr</code>. See <a class="pep reference external" href="https://peps.python.org/pep-0695/">PEP 695</a> for more details. In Python 3.16, <code class="docutils literal notranslate">AnyStr</code> will be removed from <code class="docutils literal notranslate">typing.__all__</code>, and deprecation warnings will be emitted at runtime when it is accessed or imported from <code class="docutils literal notranslate">typing</code>. <code class="docutils literal notranslate">AnyStr</code> will be removed from <code class="docutils literal notranslate">typing</code> in Python 3.18. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.LiteralString"> typing.LiteralString<a class="headerlink" href="#typing.LiteralString" title="Link to this definition">¶</a></dt> <dd>Special type that includes only literal strings. Any string literal is compatible with <code class="docutils literal notranslate">LiteralString</code>, as is another <code class="docutils literal notranslate">LiteralString</code>. However, an object typed as just <code class="docutils literal notranslate">str</code> is not. A string created by composing <code class="docutils literal notranslate">LiteralString</code>-typed objects is also acceptable as a <code class="docutils literal notranslate">LiteralString</code>. Example: <div class="highlight-python notranslate"><div class="highlight"><pre>def run_query(sql: LiteralString) -> None: ... def caller(arbitrary_string: str, literal_string: LiteralString) -> None: run_query("SELECT * FROM students") # OK run_query(literal_string) # OK run_query("SELECT * FROM " + literal_string) # OK run_query(arbitrary_string) # type checker error run_query( # type checker error f"SELECT * FROM students WHERE name = {arbitrary_string}" ) </pre></div> </div> <code class="docutils literal notranslate">LiteralString</code> is useful for sensitive APIs where arbitrary user-generated strings could generate problems. For example, the two cases above that generate type checker errors could be vulnerable to an SQL injection attack. See <a class="pep reference external" href="https://peps.python.org/pep-0675/">PEP 675</a> for more details. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Never"> typing.Never<a class="headerlink" href="#typing.Never" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="typing.NoReturn"> typing.NoReturn<a class="headerlink" href="#typing.NoReturn" title="Link to this definition">¶</a></dt> <dd><code class="xref py py-data docutils literal notranslate">Never</code> and <code class="xref py py-data docutils literal notranslate">NoReturn</code> represent the <a class="reference external" href="https://en.wikipedia.org/wiki/Bottom_type">bottom type</a>, a type that has no members. They can be used to indicate that a function never returns, such as <a class="reference internal" href="sys.html#sys.exit" title="sys.exit"><code class="xref py py-func docutils literal notranslate">sys.exit()</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import Never # or NoReturn def stop() -> Never: raise RuntimeError('no way') </pre></div> </div> Or to define a function that should never be called, as there are no valid arguments, such as <a class="reference internal" href="#typing.assert_never" title="typing.assert_never"><code class="xref py py-func docutils literal notranslate">assert_never()</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import Never # or NoReturn def never_call_me(arg: Never) -> None: pass def int_or_str(arg: int | str) -> None: never_call_me(arg) # type checker error match arg: case int(): print("It's an int") case str(): print("It's a str") case _: never_call_me(arg) # OK, arg is of type Never (or NoReturn) </pre></div> </div> <code class="xref py py-data docutils literal notranslate">Never</code> and <code class="xref py py-data docutils literal notranslate">NoReturn</code> have the same meaning in the type system and static type checkers treat both equivalently. <div class="versionadded"> Added in version 3.6.2: Added <a class="reference internal" href="#typing.NoReturn" title="typing.NoReturn"><code class="xref py py-data docutils literal notranslate">NoReturn</code></a>. </div> <div class="versionadded"> Added in version 3.11: Added <a class="reference internal" href="#typing.Never" title="typing.Never"><code class="xref py py-data docutils literal notranslate">Never</code></a>. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Self"> typing.Self<a class="headerlink" href="#typing.Self" title="Link to this definition">¶</a></dt> <dd>Special type to represent the current enclosed class. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import Self, reveal_type class Foo: def return_self(self) -> Self: ... return self class SubclassOfFoo(Foo): pass reveal_type(Foo().return_self()) # Revealed type is "Foo" reveal_type(SubclassOfFoo().return_self()) # Revealed type is "SubclassOfFoo" </pre></div> </div> This annotation is semantically equivalent to the following, albeit in a more succinct fashion: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypeVar Self = TypeVar("Self", bound="Foo") class Foo: def return_self(self: Self) -> Self: ... return self </pre></div> </div> In general, if something returns <code class="docutils literal notranslate">self</code>, as in the above examples, you should use <code class="docutils literal notranslate">Self</code> as the return annotation. If <code class="docutils literal notranslate">Foo.return_self</code> was annotated as returning <code class="docutils literal notranslate">"Foo"</code>, then the type checker would infer the object returned from <code class="docutils literal notranslate">SubclassOfFoo.return_self</code> as being of type <code class="docutils literal notranslate">Foo</code> rather than <code class="docutils literal notranslate">SubclassOfFoo</code>. Other common use cases include: <ul class="simple"> <li><a class="reference internal" href="functions.html#classmethod" title="classmethod"><code class="xref py py-class docutils literal notranslate">classmethod</code></a>s that are used as alternative constructors and return instances of the <code class="docutils literal notranslate">cls</code> parameter.</li> <li>Annotating an <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate">__enter__()</code></a> method which returns self.</li> </ul> You should not use <code class="docutils literal notranslate">Self</code> as the return annotation if the method is not guaranteed to return an instance of a subclass when the class is subclassed: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Eggs: # Self would be an incorrect return annotation here, # as the object returned is always an instance of Eggs, # even in subclasses def returns_eggs(self) -> "Eggs": return Eggs() </pre></div> </div> See <a class="pep reference external" href="https://peps.python.org/pep-0673/">PEP 673</a> for more details. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.TypeAlias"> typing.TypeAlias<a class="headerlink" href="#typing.TypeAlias" title="Link to this definition">¶</a></dt> <dd>Special annotation for explicitly declaring a <a class="reference internal" href="#type-aliases">type alias</a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypeAlias Factors: TypeAlias = list[int] </pre></div> </div> <code class="docutils literal notranslate">TypeAlias</code> is particularly useful on older Python versions for annotating aliases that make use of forward references, as it can be hard for type checkers to distinguish these from normal variable assignments: <div class="highlight-python notranslate"><div class="highlight"><pre>from typing import Generic, TypeAlias, TypeVar T = TypeVar("T") # "Box" does not exist yet, # so we have to use quotes for the forward reference on Python <3.12. # Using ``TypeAlias`` tells the type checker that this is a type alias declaration, # not a variable assignment to a string. BoxOfStrings: TypeAlias = "Box[str]" class Box(Generic[T]): @classmethod def make_box_of_strings(cls) -> BoxOfStrings: ... </pre></div> </div> See <a class="pep reference external" href="https://peps.python.org/pep-0613/">PEP 613</a> for more details. <div class="versionadded"> Added in version 3.10. </div> <div class="deprecated"> Deprecated since version 3.12: <a class="reference internal" href="#typing.TypeAlias" title="typing.TypeAlias"><code class="xref py py-data docutils literal notranslate">TypeAlias</code></a> is deprecated in favor of the <a class="reference internal" href="../reference/simple_stmts.html#type"><code class="xref std std-keyword docutils literal notranslate">type</code></a> statement, which creates instances of <a class="reference internal" href="#typing.TypeAliasType" title="typing.TypeAliasType"><code class="xref py py-class docutils literal notranslate">TypeAliasType</code></a> and which natively supports forward references. Note that while <a class="reference internal" href="#typing.TypeAlias" title="typing.TypeAlias"><code class="xref py py-data docutils literal notranslate">TypeAlias</code></a> and <a class="reference internal" href="#typing.TypeAliasType" title="typing.TypeAliasType"><code class="xref py py-class docutils literal notranslate">TypeAliasType</code></a> serve similar purposes and have similar names, they are distinct and the latter is not the type of the former. Removal of <a class="reference internal" href="#typing.TypeAlias" title="typing.TypeAlias"><code class="xref py py-data docutils literal notranslate">TypeAlias</code></a> is not currently planned, but users are encouraged to migrate to <a class="reference internal" href="../reference/simple_stmts.html#type"><code class="xref std std-keyword docutils literal notranslate">type</code></a> statements. </div> </dd></dl> </section> <section id="special-forms"> <h4>Special forms<a class="headerlink" href="#special-forms" title="Link to this heading">¶</a></h4> These can be used as types in annotations. They all support subscription using <code class="docutils literal notranslate">[]</code>, but each has a unique syntax. <dl class="py data"> <dt class="sig sig-object py" id="typing.Union"> typing.Union<a class="headerlink" href="#typing.Union" title="Link to this definition">¶</a></dt> <dd>Union type; <code class="docutils literal notranslate">Union[X, Y]</code> is equivalent to <code class="docutils literal notranslate">X | Y</code> and means either X or Y. To define a union, use e.g. <code class="docutils literal notranslate">Union[int, str]</code> or the shorthand <code class="docutils literal notranslate">int | str</code>. Using that shorthand is recommended. Details: <ul> <li>The arguments must be types and there must be at least one.</li> <li>Unions of unions are flattened, e.g.: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Union[Union[int, str], float] == Union[int, str, float] </pre></div> </div> </li> <li>Unions of a single argument vanish, e.g.: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Union[int] == int # The constructor actually returns int </pre></div> </div> </li> <li>Redundant arguments are skipped, e.g.: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Union[int, str, int] == Union[int, str] == int | str </pre></div> </div> </li> <li>When comparing unions, the argument order is ignored, e.g.: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Union[int, str] == Union[str, int] </pre></div> </div> </li> <li>You cannot subclass or instantiate a <code class="docutils literal notranslate">Union</code>.</li> <li>You cannot write <code class="docutils literal notranslate">Union[X][Y]</code>.</li> </ul> <div class="versionchanged"> Changed in version 3.7: Don’t remove explicit subclasses from unions at runtime. </div> <div class="versionchanged"> Changed in version 3.10: Unions can now be written as <code class="docutils literal notranslate">X | Y</code>. See <a class="reference internal" href="stdtypes.html#types-union">union type expressions</a>. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Optional"> typing.Optional<a class="headerlink" href="#typing.Optional" title="Link to this definition">¶</a></dt> <dd><code class="docutils literal notranslate">Optional[X]</code> is equivalent to <code class="docutils literal notranslate">X | None</code> (or <code class="docutils literal notranslate">Union[X, None]</code>). Note that this is not the same concept as an optional argument, which is one that has a default. An optional argument with a default does not require the <code class="docutils literal notranslate">Optional</code> qualifier on its type annotation just because it is optional. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def foo(arg: int = 0) -> None: ... </pre></div> </div> On the other hand, if an explicit value of <code class="docutils literal notranslate">None</code> is allowed, the use of <code class="docutils literal notranslate">Optional</code> is appropriate, whether the argument is optional or not. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def foo(arg: Optional[int] = None) -> None: ... </pre></div> </div> <div class="versionchanged"> Changed in version 3.10: Optional can now be written as <code class="docutils literal notranslate">X | None</code>. See <a class="reference internal" href="stdtypes.html#types-union">union type expressions</a>. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Concatenate"> typing.Concatenate<a class="headerlink" href="#typing.Concatenate" title="Link to this definition">¶</a></dt> <dd>Special form for annotating higher-order functions. <code class="docutils literal notranslate">Concatenate</code> can be used in conjunction with <a class="reference internal" href="#annotating-callables">Callable</a> and <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> to annotate a higher-order callable which adds, removes, or transforms parameters of another callable. Usage is in the form <code class="docutils literal notranslate">Concatenate[Arg1Type, Arg2Type, ..., ParamSpecVariable]</code>. <code class="docutils literal notranslate">Concatenate</code> is currently only valid when used as the first argument to a <a class="reference internal" href="#annotating-callables">Callable</a>. The last parameter to <code class="docutils literal notranslate">Concatenate</code> must be a <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> or ellipsis (<code class="docutils literal notranslate">...</code>). For example, to annotate a decorator <code class="docutils literal notranslate">with_lock</code> which provides a <a class="reference internal" href="threading.html#threading.Lock" title="threading.Lock"><code class="xref py py-class docutils literal notranslate">threading.Lock</code></a> to the decorated function, <code class="docutils literal notranslate">Concatenate</code> can be used to indicate that <code class="docutils literal notranslate">with_lock</code> expects a callable which takes in a <code class="docutils literal notranslate">Lock</code> as the first argument, and returns a callable with a different type signature. In this case, the <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> indicates that the returned callable’s parameter types are dependent on the parameter types of the callable being passed in: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Callable from threading import Lock from typing import Concatenate # Use this lock to ensure that only one thread is executing a function # at any time. my_lock = Lock() def with_lock[**P, R](f: Callable[Concatenate[Lock, P], R]) -> Callable[P, R]: '''A type-safe decorator which provides a lock.''' def inner(*args: P.args, **kwargs: P.kwargs) -> R: # Provide the lock as the first argument. return f(my_lock, *args, **kwargs) return inner @with_lock def sum_threadsafe(lock: Lock, numbers: list[float]) -> float: '''Add a list of numbers together in a thread-safe manner.''' with lock: return sum(numbers) # We don't need to pass in the lock ourselves thanks to the decorator. sum_threadsafe([1.1, 2.2, 3.3]) </pre></div> </div> <div class="versionadded"> Added in version 3.10. </div> <div class="admonition seealso"> See also <ul class="simple"> <li><a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a> – Parameter Specification Variables (the PEP which introduced <code class="docutils literal notranslate">ParamSpec</code> and <code class="docutils literal notranslate">Concatenate</code>)</li> <li><a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a></li> <li><a class="reference internal" href="#annotating-callables">Annotating callable objects</a></li> </ul> </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Literal"> typing.Literal<a class="headerlink" href="#typing.Literal" title="Link to this definition">¶</a></dt> <dd>Special typing form to define “literal types”. <code class="docutils literal notranslate">Literal</code> can be used to indicate to type checkers that the annotated object has a value equivalent to one of the provided literals. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def validate_simple(data: Any) -> Literal[True]: # always returns True ... type Mode = Literal['r', 'rb', 'w', 'wb'] def open_helper(file: str, mode: Mode) -> str: ... open_helper('/some/path', 'r') # Passes type check open_helper('/other/path', 'typo') # Error in type checker </pre></div> </div> <code class="docutils literal notranslate">Literal[...]</code> cannot be subclassed. At runtime, an arbitrary value is allowed as type argument to <code class="docutils literal notranslate">Literal[...]</code>, but type checkers may impose restrictions. See <a class="pep reference external" href="https://peps.python.org/pep-0586/">PEP 586</a> for more details about literal types. <div class="versionadded"> Added in version 3.8. </div> <div class="versionchanged"> Changed in version 3.9.1: <code class="docutils literal notranslate">Literal</code> now de-duplicates parameters. Equality comparisons of <code class="docutils literal notranslate">Literal</code> objects are no longer order dependent. <code class="docutils literal notranslate">Literal</code> objects will now raise a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> exception during equality comparisons if one of their parameters are not <a class="reference internal" href="../glossary.html#term-hashable">hashable</a>. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.ClassVar"> typing.ClassVar<a class="headerlink" href="#typing.ClassVar" title="Link to this definition">¶</a></dt> <dd>Special type construct to mark class variables. As introduced in <a class="pep reference external" href="https://peps.python.org/pep-0526/">PEP 526</a>, a variable annotation wrapped in ClassVar indicates that a given attribute is intended to be used as a class variable and should not be set on instances of that class. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Starship: stats: ClassVar[dict[str, int]] = {} # class variable damage: int = 10 # instance variable </pre></div> </div> <a class="reference internal" href="#typing.ClassVar" title="typing.ClassVar"><code class="xref py py-data docutils literal notranslate">ClassVar</code></a> accepts only types and cannot be further subscribed. <a class="reference internal" href="#typing.ClassVar" title="typing.ClassVar"><code class="xref py py-data docutils literal notranslate">ClassVar</code></a> is not a class itself, and should not be used with <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> or <a class="reference internal" href="functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate">issubclass()</code></a>. <a class="reference internal" href="#typing.ClassVar" title="typing.ClassVar"><code class="xref py py-data docutils literal notranslate">ClassVar</code></a> does not change Python runtime behavior, but it can be used by third-party type checkers. For example, a type checker might flag the following code as an error: <div class="highlight-python3 notranslate"><div class="highlight"><pre>enterprise_d = Starship(3000) enterprise_d.stats = {} # Error, setting class variable on instance Starship.stats = {} # This is OK </pre></div> </div> <div class="versionadded"> Added in version 3.5.3. </div> <div class="versionchanged"> Changed in version 3.13: <a class="reference internal" href="#typing.ClassVar" title="typing.ClassVar"><code class="xref py py-data docutils literal notranslate">ClassVar</code></a> can now be nested in <a class="reference internal" href="#typing.Final" title="typing.Final"><code class="xref py py-data docutils literal notranslate">Final</code></a> and vice versa. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Final"> typing.Final<a class="headerlink" href="#typing.Final" title="Link to this definition">¶</a></dt> <dd>Special typing construct to indicate final names to type checkers. Final names cannot be reassigned in any scope. Final names declared in class scopes cannot be overridden in subclasses. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>MAX_SIZE: Final = 9000 MAX_SIZE += 1 # Error reported by type checker class Connection: TIMEOUT: Final[int] = 10 class FastConnector(Connection): TIMEOUT = 1 # Error reported by type checker </pre></div> </div> There is no runtime checking of these properties. See <a class="pep reference external" href="https://peps.python.org/pep-0591/">PEP 591</a> for more details. <div class="versionadded"> Added in version 3.8. </div> <div class="versionchanged"> Changed in version 3.13: <a class="reference internal" href="#typing.Final" title="typing.Final"><code class="xref py py-data docutils literal notranslate">Final</code></a> can now be nested in <a class="reference internal" href="#typing.ClassVar" title="typing.ClassVar"><code class="xref py py-data docutils literal notranslate">ClassVar</code></a> and vice versa. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Required"> typing.Required<a class="headerlink" href="#typing.Required" title="Link to this definition">¶</a></dt> <dd>Special typing construct to mark a <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a> key as required. This is mainly useful for <code class="docutils literal notranslate">total=False</code> TypedDicts. See <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a> and <a class="pep reference external" href="https://peps.python.org/pep-0655/">PEP 655</a> for more details. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.NotRequired"> typing.NotRequired<a class="headerlink" href="#typing.NotRequired" title="Link to this definition">¶</a></dt> <dd>Special typing construct to mark a <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a> key as potentially missing. See <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a> and <a class="pep reference external" href="https://peps.python.org/pep-0655/">PEP 655</a> for more details. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.ReadOnly"> typing.ReadOnly<a class="headerlink" href="#typing.ReadOnly" title="Link to this definition">¶</a></dt> <dd>A special typing construct to mark an item of a <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a> as read-only. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Movie(TypedDict): title: ReadOnly[str] year: int def mutate_movie(m: Movie) -> None: m["year"] = 1999 # allowed m["title"] = "The Matrix" # typechecker error </pre></div> </div> There is no runtime checking for this property. See <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a> and <a class="pep reference external" href="https://peps.python.org/pep-0705/">PEP 705</a> for more details. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Annotated"> typing.Annotated<a class="headerlink" href="#typing.Annotated" title="Link to this definition">¶</a></dt> <dd>Special typing form to add context-specific metadata to an annotation. Add metadata <code class="docutils literal notranslate">x</code> to a given type <code class="docutils literal notranslate">T</code> by using the annotation <code class="docutils literal notranslate">Annotated[T, x]</code>. Metadata added using <code class="docutils literal notranslate">Annotated</code> can be used by static analysis tools or at runtime. At runtime, the metadata is stored in a <code class="xref py py-attr docutils literal notranslate">__metadata__</code> attribute. If a library or tool encounters an annotation <code class="docutils literal notranslate">Annotated[T, x]</code> and has no special logic for the metadata, it should ignore the metadata and simply treat the annotation as <code class="docutils literal notranslate">T</code>. As such, <code class="docutils literal notranslate">Annotated</code> can be useful for code that wants to use annotations for purposes outside Python’s static typing system. Using <code class="docutils literal notranslate">Annotated[T, x]</code> as an annotation still allows for static typechecking of <code class="docutils literal notranslate">T</code>, as type checkers will simply ignore the metadata <code class="docutils literal notranslate">x</code>. In this way, <code class="docutils literal notranslate">Annotated</code> differs from the <a class="reference internal" href="#typing.no_type_check" title="typing.no_type_check"><code class="xref py py-func docutils literal notranslate">@no_type_check</code></a> decorator, which can also be used for adding annotations outside the scope of the typing system, but completely disables typechecking for a function or class. The responsibility of how to interpret the metadata lies with the tool or library encountering an <code class="docutils literal notranslate">Annotated</code> annotation. A tool or library encountering an <code class="docutils literal notranslate">Annotated</code> type can scan through the metadata elements to determine if they are of interest (e.g., using <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a>). <dl class="describe"> <dt class="sig sig-object"> Annotated[<type>, <metadata>]</dt> <dd></dd></dl> Here is an example of how you might use <code class="docutils literal notranslate">Annotated</code> to add metadata to type annotations if you were doing range analysis: <div class="highlight-python notranslate"><div class="highlight"><pre>@dataclass class ValueRange: lo: int hi: int T1 = Annotated[int, ValueRange(-10, 5)] T2 = Annotated[T1, ValueRange(-20, 3)] </pre></div> </div> Details of the syntax: <ul> <li>The first argument to <code class="docutils literal notranslate">Annotated</code> must be a valid type</li> <li>Multiple metadata elements can be supplied (<code class="docutils literal notranslate">Annotated</code> supports variadic arguments): <div class="highlight-python3 notranslate"><div class="highlight"><pre>@dataclass class ctype: kind: str Annotated[int, ValueRange(3, 10), ctype("char")] </pre></div> </div> It is up to the tool consuming the annotations to decide whether the client is allowed to add multiple metadata elements to one annotation and how to merge those annotations. </li> <li><code class="docutils literal notranslate">Annotated</code> must be subscripted with at least two arguments ( <code class="docutils literal notranslate">Annotated[int]</code> is not valid)</li> <li>The order of the metadata elements is preserved and matters for equality checks: <div class="highlight-python3 notranslate"><div class="highlight"><pre>assert Annotated[int, ValueRange(3, 10), ctype("char")] != Annotated[ int, ctype("char"), ValueRange(3, 10) ] </pre></div> </div> </li> <li>Nested <code class="docutils literal notranslate">Annotated</code> types are flattened. The order of the metadata elements starts with the innermost annotation: <div class="highlight-python3 notranslate"><div class="highlight"><pre>assert Annotated[Annotated[int, ValueRange(3, 10)], ctype("char")] == Annotated[ int, ValueRange(3, 10), ctype("char") ] </pre></div> </div> </li> <li>Duplicated metadata elements are not removed: <div class="highlight-python3 notranslate"><div class="highlight"><pre>assert Annotated[int, ValueRange(3, 10)] != Annotated[ int, ValueRange(3, 10), ValueRange(3, 10) ] </pre></div> </div> </li> <li><code class="docutils literal notranslate">Annotated</code> can be used with nested and generic aliases: <div class="highlight-python notranslate"><div class="highlight"><pre>@dataclass class MaxLen: value: int type Vec[T] = Annotated[list[tuple[T, T]], MaxLen(10)] # When used in a type annotation, a type checker will treat "V" the same as # ``Annotated[list[tuple[int, int]], MaxLen(10)]``: type V = Vec[int] </pre></div> </div> </li> <li><code class="docutils literal notranslate">Annotated</code> cannot be used with an unpacked <a class="reference internal" href="#typing.TypeVarTuple" title="typing.TypeVarTuple"><code class="xref py py-class docutils literal notranslate">TypeVarTuple</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>type Variadic[*Ts] = Annotated[*Ts, Ann1] # NOT valid </pre></div> </div> This would be equivalent to: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Annotated[T1, T2, T3, ..., Ann1] </pre></div> </div> where <code class="docutils literal notranslate">T1</code>, <code class="docutils literal notranslate">T2</code>, etc. are <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal notranslate">TypeVars</code></a>. This would be invalid: only one type should be passed to Annotated. </li> <li>By default, <a class="reference internal" href="#typing.get_type_hints" title="typing.get_type_hints"><code class="xref py py-func docutils literal notranslate">get_type_hints()</code></a> strips the metadata from annotations. Pass <code class="docutils literal notranslate">include_extras=True</code> to have the metadata preserved: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> from typing import Annotated, get_type_hints >>> def func(x: Annotated[int, "metadata"]) -> None: pass ... >>> get_type_hints(func) {'x': <class 'int'>, 'return': <class 'NoneType'>} >>> get_type_hints(func, include_extras=True) {'x': typing.Annotated[int, 'metadata'], 'return': <class 'NoneType'>} </pre></div> </div> </li> <li>At runtime, the metadata associated with an <code class="docutils literal notranslate">Annotated</code> type can be retrieved via the <code class="xref py py-attr docutils literal notranslate">__metadata__</code> attribute: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> from typing import Annotated >>> X = Annotated[int, "very", "important", "metadata"] >>> X typing.Annotated[int, 'very', 'important', 'metadata'] >>> X.__metadata__ ('very', 'important', 'metadata') </pre></div> </div> </li> <li>At runtime, if you want to retrieve the original type wrapped by <code class="docutils literal notranslate">Annotated</code>, use the <code class="xref py py-attr docutils literal notranslate">__origin__</code> attribute: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> from typing import Annotated, get_origin >>> Password = Annotated[str, "secret"] >>> Password.__origin__ <class 'str'> </pre></div> </div> Note that using <a class="reference internal" href="#typing.get_origin" title="typing.get_origin"><code class="xref py py-func docutils literal notranslate">get_origin()</code></a> will return <code class="docutils literal notranslate">Annotated</code> itself: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> get_origin(Password) typing.Annotated </pre></div> </div> </li> </ul> <div class="admonition seealso"> See also <dl class="simple"> <dt><a class="pep reference external" href="https://peps.python.org/pep-0593/">PEP 593</a> - Flexible function and variable annotations</dt><dd>The PEP introducing <code class="docutils literal notranslate">Annotated</code> to the standard library. </dd> </dl> </div> <div class="versionadded"> Added in version 3.9. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.TypeIs"> typing.TypeIs<a class="headerlink" href="#typing.TypeIs" title="Link to this definition">¶</a></dt> <dd>Special typing construct for marking user-defined type predicate functions. <code class="docutils literal notranslate">TypeIs</code> can be used to annotate the return type of a user-defined type predicate function. <code class="docutils literal notranslate">TypeIs</code> only accepts a single type argument. At runtime, functions marked this way should return a boolean and take at least one positional argument. <code class="docutils literal notranslate">TypeIs</code> aims to benefit type narrowing – a technique used by static type checkers to determine a more precise type of an expression within a program’s code flow. Usually type narrowing is done by analyzing conditional code flow and applying the narrowing to a block of code. The conditional expression here is sometimes referred to as a “type predicate”: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def is_str(val: str | float): # "isinstance" type predicate if isinstance(val, str): # Type of ``val`` is narrowed to ``str`` ... else: # Else, type of ``val`` is narrowed to ``float``. ... </pre></div> </div> Sometimes it would be convenient to use a user-defined boolean function as a type predicate. Such a function should use <code class="docutils literal notranslate">TypeIs[...]</code> or <a class="reference internal" href="#typing.TypeGuard" title="typing.TypeGuard"><code class="xref py py-data docutils literal notranslate">TypeGuard</code></a> as its return type to alert static type checkers to this intention. <code class="docutils literal notranslate">TypeIs</code> usually has more intuitive behavior than <code class="docutils literal notranslate">TypeGuard</code>, but it cannot be used when the input and output types are incompatible (e.g., <code class="docutils literal notranslate">list[object]</code> to <code class="docutils literal notranslate">list[int]</code>) or when the function does not return <code class="docutils literal notranslate">True</code> for all instances of the narrowed type. Using <code class="docutils literal notranslate">-> TypeIs[NarrowedType]</code> tells the static type checker that for a given function: <ol class="arabic simple"> <li>The return value is a boolean.</li> <li>If the return value is <code class="docutils literal notranslate">True</code>, the type of its argument is the intersection of the argument’s original type and <code class="docutils literal notranslate">NarrowedType</code>.</li> <li>If the return value is <code class="docutils literal notranslate">False</code>, the type of its argument is narrowed to exclude <code class="docutils literal notranslate">NarrowedType</code>.</li> </ol> For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import assert_type, final, TypeIs class Parent: pass class Child(Parent): pass @final class Unrelated: pass def is_parent(val: object) -> TypeIs[Parent]: return isinstance(val, Parent) def run(arg: Child | Unrelated): if is_parent(arg): # Type of ``arg`` is narrowed to the intersection # of ``Parent`` and ``Child``, which is equivalent to # ``Child``. assert_type(arg, Child) else: # Type of ``arg`` is narrowed to exclude ``Parent``, # so only ``Unrelated`` is left. assert_type(arg, Unrelated) </pre></div> </div> The type inside <code class="docutils literal notranslate">TypeIs</code> must be consistent with the type of the function’s argument; if it is not, static type checkers will raise an error. An incorrectly written <code class="docutils literal notranslate">TypeIs</code> function can lead to unsound behavior in the type system; it is the user’s responsibility to write such functions in a type-safe manner. If a <code class="docutils literal notranslate">TypeIs</code> function is a class or instance method, then the type in <code class="docutils literal notranslate">TypeIs</code> maps to the type of the second parameter (after <code class="docutils literal notranslate">cls</code> or <code class="docutils literal notranslate">self</code>). In short, the form <code class="docutils literal notranslate">def foo(arg: TypeA) -> TypeIs[TypeB]: ...</code>, means that if <code class="docutils literal notranslate">foo(arg)</code> returns <code class="docutils literal notranslate">True</code>, then <code class="docutils literal notranslate">arg</code> is an instance of <code class="docutils literal notranslate">TypeB</code>, and if it returns <code class="docutils literal notranslate">False</code>, it is not an instance of <code class="docutils literal notranslate">TypeB</code>. <code class="docutils literal notranslate">TypeIs</code> also works with type variables. For more information, see <a class="pep reference external" href="https://peps.python.org/pep-0742/">PEP 742</a> (Narrowing types with <code class="docutils literal notranslate">TypeIs</code>). <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.TypeGuard"> typing.TypeGuard<a class="headerlink" href="#typing.TypeGuard" title="Link to this definition">¶</a></dt> <dd>Special typing construct for marking user-defined type predicate functions. Type predicate functions are user-defined functions that return whether their argument is an instance of a particular type. <code class="docutils literal notranslate">TypeGuard</code> works similarly to <a class="reference internal" href="#typing.TypeIs" title="typing.TypeIs"><code class="xref py py-data docutils literal notranslate">TypeIs</code></a>, but has subtly different effects on type checking behavior (see below). Using <code class="docutils literal notranslate">-> TypeGuard</code> tells the static type checker that for a given function: <ol class="arabic simple"> <li>The return value is a boolean.</li> <li>If the return value is <code class="docutils literal notranslate">True</code>, the type of its argument is the type inside <code class="docutils literal notranslate">TypeGuard</code>.</li> </ol> <code class="docutils literal notranslate">TypeGuard</code> also works with type variables. See <a class="pep reference external" href="https://peps.python.org/pep-0647/">PEP 647</a> for more details. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def is_str_list(val: list[object]) -> TypeGuard[list[str]]: '''Determines whether all objects in the list are strings''' return all(isinstance(x, str) for x in val) def func1(val: list[object]): if is_str_list(val): # Type of ``val`` is narrowed to ``list[str]``. print(" ".join(val)) else: # Type of ``val`` remains as ``list[object]``. print("Not a list of strings!") </pre></div> </div> <code class="docutils literal notranslate">TypeIs</code> and <code class="docutils literal notranslate">TypeGuard</code> differ in the following ways: <ul class="simple"> <li><code class="docutils literal notranslate">TypeIs</code> requires the narrowed type to be a subtype of the input type, while <code class="docutils literal notranslate">TypeGuard</code> does not. The main reason is to allow for things like narrowing <code class="docutils literal notranslate">list[object]</code> to <code class="docutils literal notranslate">list[str]</code> even though the latter is not a subtype of the former, since <code class="docutils literal notranslate">list</code> is invariant.</li> <li>When a <code class="docutils literal notranslate">TypeGuard</code> function returns <code class="docutils literal notranslate">True</code>, type checkers narrow the type of the variable to exactly the <code class="docutils literal notranslate">TypeGuard</code> type. When a <code class="docutils literal notranslate">TypeIs</code> function returns <code class="docutils literal notranslate">True</code>, type checkers can infer a more precise type combining the previously known type of the variable with the <code class="docutils literal notranslate">TypeIs</code> type. (Technically, this is known as an intersection type.)</li> <li>When a <code class="docutils literal notranslate">TypeGuard</code> function returns <code class="docutils literal notranslate">False</code>, type checkers cannot narrow the type of the variable at all. When a <code class="docutils literal notranslate">TypeIs</code> function returns <code class="docutils literal notranslate">False</code>, type checkers can narrow the type of the variable to exclude the <code class="docutils literal notranslate">TypeIs</code> type.</li> </ul> <div class="versionadded"> Added in version 3.10. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Unpack"> typing.Unpack<a class="headerlink" href="#typing.Unpack" title="Link to this definition">¶</a></dt> <dd>Typing operator to conceptually mark an object as having been unpacked. For example, using the unpack operator <code class="docutils literal notranslate">*</code> on a <a class="reference internal" href="#typevartuple">type variable tuple</a> is equivalent to using <code class="docutils literal notranslate">Unpack</code> to mark the type variable tuple as having been unpacked: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Ts = TypeVarTuple('Ts') tup: tuple[*Ts] # Effectively does: tup: tuple[Unpack[Ts]] </pre></div> </div> In fact, <code class="docutils literal notranslate">Unpack</code> can be used interchangeably with <code class="docutils literal notranslate">*</code> in the context of <a class="reference internal" href="#typing.TypeVarTuple" title="typing.TypeVarTuple"><code class="xref py py-class docutils literal notranslate">typing.TypeVarTuple</code></a> and <a class="reference internal" href="stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">builtins.tuple</code></a> types. You might see <code class="docutils literal notranslate">Unpack</code> being used explicitly in older versions of Python, where <code class="docutils literal notranslate">*</code> couldn’t be used in certain places: <div class="highlight-python3 notranslate"><div class="highlight"><pre># In older versions of Python, TypeVarTuple and Unpack # are located in the `typing_extensions` backports package. from typing_extensions import TypeVarTuple, Unpack Ts = TypeVarTuple('Ts') tup: tuple[*Ts] # Syntax error on Python <= 3.10! tup: tuple[Unpack[Ts]] # Semantically equivalent, and backwards-compatible </pre></div> </div> <code class="docutils literal notranslate">Unpack</code> can also be used along with <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">typing.TypedDict</code></a> for typing <code class="docutils literal notranslate">**kwargs</code> in a function signature: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from typing import TypedDict, Unpack class Movie(TypedDict): name: str year: int # This function expects two keyword arguments - `name` of type `str` # and `year` of type `int`. def foo(**kwargs: Unpack[Movie]): ... </pre></div> </div> See <a class="pep reference external" href="https://peps.python.org/pep-0692/">PEP 692</a> for more details on using <code class="docutils literal notranslate">Unpack</code> for <code class="docutils literal notranslate">**kwargs</code> typing. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> </section> <section id="building-generic-types-and-type-aliases"> <h4>Building generic types and type aliases<a class="headerlink" href="#building-generic-types-and-type-aliases" title="Link to this heading">¶</a></h4> The following classes should not be used directly as annotations. Their intended purpose is to be building blocks for creating generic types and type aliases. These objects can be created through special syntax (<a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter lists</a> and the <a class="reference internal" href="../reference/simple_stmts.html#type"><code class="xref std std-keyword docutils literal notranslate">type</code></a> statement). For compatibility with Python 3.11 and earlier, they can also be created without the dedicated syntax, as documented below. <dl class="py class"> <dt class="sig sig-object py" id="typing.Generic"> class typing.Generic<a class="headerlink" href="#typing.Generic" title="Link to this definition">¶</a></dt> <dd>Abstract base class for generic types. A generic type is typically declared by adding a list of type parameters after the class name: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Mapping[KT, VT]: def __getitem__(self, key: KT) -> VT: ... # Etc. </pre></div> </div> Such a class implicitly inherits from <code class="docutils literal notranslate">Generic</code>. The runtime semantics of this syntax are discussed in the <a class="reference internal" href="../reference/compound_stmts.html#generic-classes">Language Reference</a>. This class can then be used as follows: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def lookup_name[X, Y](mapping: Mapping[X, Y], key: X, default: Y) -> Y: try: return mapping[key] except KeyError: return default </pre></div> </div> Here the brackets after the function name indicate a <a class="reference internal" href="../reference/compound_stmts.html#generic-functions">generic function</a>. For backwards compatibility, generic classes can also be declared by explicitly inheriting from <code class="docutils literal notranslate">Generic</code>. In this case, the type parameters must be declared separately: <div class="highlight-python3 notranslate"><div class="highlight"><pre>KT = TypeVar('KT') VT = TypeVar('VT') class Mapping(Generic[KT, VT]): def __getitem__(self, key: KT) -> VT: ... # Etc. </pre></div> </div> </dd></dl> <dl class="py class" id="typevar"> <dt class="sig sig-object py" id="typing.TypeVar"> class typing.TypeVar(name, *constraints, bound=None, covariant=False, contravariant=False, infer_variance=False, default=typing.NoDefault)<a class="headerlink" href="#typing.TypeVar" title="Link to this definition">¶</a></dt> <dd>Type variable. The preferred way to construct a type variable is via the dedicated syntax for <a class="reference internal" href="../reference/compound_stmts.html#generic-functions">generic functions</a>, <a class="reference internal" href="../reference/compound_stmts.html#generic-classes">generic classes</a>, and <a class="reference internal" href="../reference/compound_stmts.html#generic-type-aliases">generic type aliases</a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Sequence[T]: # T is a TypeVar ... </pre></div> </div> This syntax can also be used to create bounded and constrained type variables: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class StrSequence[S: str]: # S is a TypeVar with a `str` upper bound; ... # we can say that S is "bounded by `str`" class StrOrBytesSequence[A: (str, bytes)]: # A is a TypeVar constrained to str or bytes ... </pre></div> </div> However, if desired, reusable type variables can also be constructed manually, like so: <div class="highlight-python3 notranslate"><div class="highlight"><pre>T = TypeVar('T') # Can be anything S = TypeVar('S', bound=str) # Can be any subtype of str A = TypeVar('A', str, bytes) # Must be exactly str or bytes </pre></div> </div> Type variables exist primarily for the benefit of static type checkers. They serve as the parameters for generic types as well as for generic function and type alias definitions. See <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> for more information on generic types. Generic functions work as follows: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def repeat[T](x: T, n: int) -> Sequence[T]: """Return a list containing n references to x.""" return [x]*n def print_capitalized[S: str](x: S) -> S: """Print x capitalized, and return x.""" print(x.capitalize()) return x def concatenate[A: (str, bytes)](x: A, y: A) -> A: """Add two strings or bytes objects together.""" return x + y </pre></div> </div> Note that type variables can be bounded, constrained, or neither, but cannot be both bounded and constrained. The variance of type variables is inferred by type checkers when they are created through the <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter syntax</a> or when <code class="docutils literal notranslate">infer_variance=True</code> is passed. Manually created type variables may be explicitly marked covariant or contravariant by passing <code class="docutils literal notranslate">covariant=True</code> or <code class="docutils literal notranslate">contravariant=True</code>. By default, manually created type variables are invariant. See <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> and <a class="pep reference external" href="https://peps.python.org/pep-0695/">PEP 695</a> for more details. Bounded type variables and constrained type variables have different semantics in several important ways. Using a bounded type variable means that the <code class="docutils literal notranslate">TypeVar</code> will be solved using the most specific type possible: <div class="highlight-python3 notranslate"><div class="highlight"><pre>x = print_capitalized('a string') reveal_type(x) # revealed type is str class StringSubclass(str): pass y = print_capitalized(StringSubclass('another string')) reveal_type(y) # revealed type is StringSubclass z = print_capitalized(45) # error: int is not a subtype of str </pre></div> </div> The upper bound of a type variable can be a concrete type, abstract type (ABC or Protocol), or even a union of types: <div class="highlight-python3 notranslate"><div class="highlight"><pre># Can be anything with an __abs__ method def print_abs[T: SupportsAbs](arg: T) -> None: print("Absolute value:", abs(arg)) U = TypeVar('U', bound=str|bytes) # Can be any subtype of the union str|bytes V = TypeVar('V', bound=SupportsAbs) # Can be anything with an __abs__ method </pre></div> </div> Using a constrained type variable, however, means that the <code class="docutils literal notranslate">TypeVar</code> can only ever be solved as being exactly one of the constraints given: <div class="highlight-python3 notranslate"><div class="highlight"><pre>a = concatenate('one', 'two') reveal_type(a) # revealed type is str b = concatenate(StringSubclass('one'), StringSubclass('two')) reveal_type(b) # revealed type is str, despite StringSubclass being passed in c = concatenate('one', b'two') # error: type variable 'A' can be either str or bytes in a function call, but not both </pre></div> </div> At runtime, <code class="docutils literal notranslate">isinstance(x, T)</code> will raise <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>. <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__name__"> __name__<a class="headerlink" href="#typing.TypeVar.__name__" title="Link to this definition">¶</a></dt> <dd>The name of the type variable. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__covariant__"> __covariant__<a class="headerlink" href="#typing.TypeVar.__covariant__" title="Link to this definition">¶</a></dt> <dd>Whether the type var has been explicitly marked as covariant. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__contravariant__"> __contravariant__<a class="headerlink" href="#typing.TypeVar.__contravariant__" title="Link to this definition">¶</a></dt> <dd>Whether the type var has been explicitly marked as contravariant. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__infer_variance__"> __infer_variance__<a class="headerlink" href="#typing.TypeVar.__infer_variance__" title="Link to this definition">¶</a></dt> <dd>Whether the type variable’s variance should be inferred by type checkers. <div class="versionadded"> Added in version 3.12. </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__bound__"> __bound__<a class="headerlink" href="#typing.TypeVar.__bound__" title="Link to this definition">¶</a></dt> <dd>The upper bound of the type variable, if any. <div class="versionchanged"> Changed in version 3.12: For type variables created through <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter syntax</a>, the bound is evaluated only when the attribute is accessed, not when the type variable is created (see <a class="reference internal" href="../reference/executionmodel.html#lazy-evaluation">Lazy evaluation</a>). </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__constraints__"> __constraints__<a class="headerlink" href="#typing.TypeVar.__constraints__" title="Link to this definition">¶</a></dt> <dd>A tuple containing the constraints of the type variable, if any. <div class="versionchanged"> Changed in version 3.12: For type variables created through <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter syntax</a>, the constraints are evaluated only when the attribute is accessed, not when the type variable is created (see <a class="reference internal" href="../reference/executionmodel.html#lazy-evaluation">Lazy evaluation</a>). </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVar.__default__"> __default__<a class="headerlink" href="#typing.TypeVar.__default__" title="Link to this definition">¶</a></dt> <dd>The default value of the type variable, or <a class="reference internal" href="#typing.NoDefault" title="typing.NoDefault"><code class="xref py py-data docutils literal notranslate">typing.NoDefault</code></a> if it has no default. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="typing.TypeVar.has_default"> has_default()<a class="headerlink" href="#typing.TypeVar.has_default" title="Link to this definition">¶</a></dt> <dd>Return whether or not the type variable has a default value. This is equivalent to checking whether <a class="reference internal" href="#typing.TypeVar.__default__" title="typing.TypeVar.__default__"><code class="xref py py-attr docutils literal notranslate">__default__</code></a> is not the <a class="reference internal" href="#typing.NoDefault" title="typing.NoDefault"><code class="xref py py-data docutils literal notranslate">typing.NoDefault</code></a> singleton, except that it does not force evaluation of the <a class="reference internal" href="../reference/executionmodel.html#lazy-evaluation">lazily evaluated</a> default value. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <div class="versionchanged"> Changed in version 3.12: Type variables can now be declared using the <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter</a> syntax introduced by <a class="pep reference external" href="https://peps.python.org/pep-0695/">PEP 695</a>. The <code class="docutils literal notranslate">infer_variance</code> parameter was added. </div> <div class="versionchanged"> Changed in version 3.13: Support for default values was added. </div> </dd></dl> <dl class="py class" id="typevartuple"> <dt class="sig sig-object py" id="typing.TypeVarTuple"> class typing.TypeVarTuple(name, *, default=typing.NoDefault)<a class="headerlink" href="#typing.TypeVarTuple" title="Link to this definition">¶</a></dt> <dd>Type variable tuple. A specialized form of <a class="reference internal" href="#typevar">type variable</a> that enables variadic generics. Type variable tuples can be declared in <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter lists</a> using a single asterisk (<code class="docutils literal notranslate">*</code>) before the name: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def move_first_element_to_last[T, *Ts](tup: tuple[T, *Ts]) -> tuple[*Ts, T]: return (*tup[1:], tup[0]) </pre></div> </div> Or by explicitly invoking the <code class="docutils literal notranslate">TypeVarTuple</code> constructor: <div class="highlight-python3 notranslate"><div class="highlight"><pre>T = TypeVar("T") Ts = TypeVarTuple("Ts") def move_first_element_to_last(tup: tuple[T, *Ts]) -> tuple[*Ts, T]: return (*tup[1:], tup[0]) </pre></div> </div> A normal type variable enables parameterization with a single type. A type variable tuple, in contrast, allows parameterization with an arbitrary number of types by acting like an arbitrary number of type variables wrapped in a tuple. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre># T is bound to int, Ts is bound to () # Return value is (1,), which has type tuple[int] move_first_element_to_last(tup=(1,)) # T is bound to int, Ts is bound to (str,) # Return value is ('spam', 1), which has type tuple[str, int] move_first_element_to_last(tup=(1, 'spam')) # T is bound to int, Ts is bound to (str, float) # Return value is ('spam', 3.0, 1), which has type tuple[str, float, int] move_first_element_to_last(tup=(1, 'spam', 3.0)) # This fails to type check (and fails at runtime) # because tuple[()] is not compatible with tuple[T, *Ts] # (at least one element is required) move_first_element_to_last(tup=()) </pre></div> </div> Note the use of the unpacking operator <code class="docutils literal notranslate">*</code> in <code class="docutils literal notranslate">tuple[T, *Ts]</code>. Conceptually, you can think of <code class="docutils literal notranslate">Ts</code> as a tuple of type variables <code class="docutils literal notranslate">(T1, T2, ...)</code>. <code class="docutils literal notranslate">tuple[T, *Ts]</code> would then become <code class="docutils literal notranslate">tuple[T, *(T1, T2, ...)]</code>, which is equivalent to <code class="docutils literal notranslate">tuple[T, T1, T2, ...]</code>. (Note that in older versions of Python, you might see this written using <a class="reference internal" href="#typing.Unpack" title="typing.Unpack"><code class="xref py py-data docutils literal notranslate">Unpack</code></a> instead, as <code class="docutils literal notranslate">Unpack[Ts]</code>.) Type variable tuples must always be unpacked. This helps distinguish type variable tuples from normal type variables: <div class="highlight-python3 notranslate"><div class="highlight"><pre>x: Ts # Not valid x: tuple[Ts] # Not valid x: tuple[*Ts] # The correct way to do it </pre></div> </div> Type variable tuples can be used in the same contexts as normal type variables. For example, in class definitions, arguments, and return types: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Array[*Shape]: def __getitem__(self, key: tuple[*Shape]) -> float: ... def __abs__(self) -> "Array[*Shape]": ... def get_shape(self) -> tuple[*Shape]: ... </pre></div> </div> Type variable tuples can be happily combined with normal type variables: <div class="highlight-python notranslate"><div class="highlight"><pre>class Array[DType, *Shape]: # This is fine pass class Array2[*Shape, DType]: # This would also be fine pass class Height: ... class Width: ... float_array_1d: Array[float, Height] = Array() # Totally fine int_array_2d: Array[int, Height, Width] = Array() # Yup, fine too </pre></div> </div> However, note that at most one type variable tuple may appear in a single list of type arguments or type parameters: <div class="highlight-python3 notranslate"><div class="highlight"><pre>x: tuple[*Ts, *Ts] # Not valid class Array[*Shape, *Shape]: # Not valid pass </pre></div> </div> Finally, an unpacked type variable tuple can be used as the type annotation of <code class="docutils literal notranslate">*args</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def call_soon[*Ts]( callback: Callable[[*Ts], None], *args: *Ts ) -> None: ... callback(*args) </pre></div> </div> In contrast to non-unpacked annotations of <code class="docutils literal notranslate">*args</code> - e.g. <code class="docutils literal notranslate">*args: int</code>, which would specify that all arguments are <code class="docutils literal notranslate">int</code> - <code class="docutils literal notranslate">*args: *Ts</code> enables reference to the types of the individual arguments in <code class="docutils literal notranslate">*args</code>. Here, this allows us to ensure the types of the <code class="docutils literal notranslate">*args</code> passed to <code class="docutils literal notranslate">call_soon</code> match the types of the (positional) arguments of <code class="docutils literal notranslate">callback</code>. See <a class="pep reference external" href="https://peps.python.org/pep-0646/">PEP 646</a> for more details on type variable tuples. <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVarTuple.__name__"> __name__<a class="headerlink" href="#typing.TypeVarTuple.__name__" title="Link to this definition">¶</a></dt> <dd>The name of the type variable tuple. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeVarTuple.__default__"> __default__<a class="headerlink" href="#typing.TypeVarTuple.__default__" title="Link to this definition">¶</a></dt> <dd>The default value of the type variable tuple, or <a class="reference internal" href="#typing.NoDefault" title="typing.NoDefault"><code class="xref py py-data docutils literal notranslate">typing.NoDefault</code></a> if it has no default. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="typing.TypeVarTuple.has_default"> has_default()<a class="headerlink" href="#typing.TypeVarTuple.has_default" title="Link to this definition">¶</a></dt> <dd>Return whether or not the type variable tuple has a default value. This is equivalent to checking whether <a class="reference internal" href="#typing.TypeVarTuple.__default__" title="typing.TypeVarTuple.__default__"><code class="xref py py-attr docutils literal notranslate">__default__</code></a> is not the <a class="reference internal" href="#typing.NoDefault" title="typing.NoDefault"><code class="xref py py-data docutils literal notranslate">typing.NoDefault</code></a> singleton, except that it does not force evaluation of the <a class="reference internal" href="../reference/executionmodel.html#lazy-evaluation">lazily evaluated</a> default value. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <div class="versionadded"> Added in version 3.11. </div> <div class="versionchanged"> Changed in version 3.12: Type variable tuples can now be declared using the <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter</a> syntax introduced by <a class="pep reference external" href="https://peps.python.org/pep-0695/">PEP 695</a>. </div> <div class="versionchanged"> Changed in version 3.13: Support for default values was added. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.ParamSpec"> class typing.ParamSpec(name, *, bound=None, covariant=False, contravariant=False, default=typing.NoDefault)<a class="headerlink" href="#typing.ParamSpec" title="Link to this definition">¶</a></dt> <dd>Parameter specification variable. A specialized version of <a class="reference internal" href="#typevar">type variables</a>. In <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter lists</a>, parameter specifications can be declared with two asterisks (<code class="docutils literal notranslate">**</code>): <div class="highlight-python3 notranslate"><div class="highlight"><pre>type IntFunc[**P] = Callable[P, int] </pre></div> </div> For compatibility with Python 3.11 and earlier, <code class="docutils literal notranslate">ParamSpec</code> objects can also be created as follows: <div class="highlight-python3 notranslate"><div class="highlight"><pre>P = ParamSpec('P') </pre></div> </div> Parameter specification variables exist primarily for the benefit of static type checkers. They are used to forward the parameter types of one callable to another callable – a pattern commonly found in higher order functions and decorators. They are only valid when used in <code class="docutils literal notranslate">Concatenate</code>, or as the first argument to <code class="docutils literal notranslate">Callable</code>, or as parameters for user-defined Generics. See <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> for more information on generic types. For example, to add basic logging to a function, one can create a decorator <code class="docutils literal notranslate">add_logging</code> to log function calls. The parameter specification variable tells the type checker that the callable passed into the decorator and the new callable returned by it have inter-dependent type parameters: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from collections.abc import Callable import logging def add_logging[T, **P](f: Callable[P, T]) -> Callable[P, T]: '''A type-safe decorator to add logging to a function.''' def inner(*args: P.args, **kwargs: P.kwargs) -> T: logging.info(f'{f.__name__} was called') return f(*args, **kwargs) return inner @add_logging def add_two(x: float, y: float) -> float: '''Add two numbers together.''' return x + y </pre></div> </div> Without <code class="docutils literal notranslate">ParamSpec</code>, the simplest way to annotate this previously was to use a <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal notranslate">TypeVar</code></a> with upper bound <code class="docutils literal notranslate">Callable[..., Any]</code>. However this causes two problems: <ol class="arabic simple"> <li>The type checker can’t type check the <code class="docutils literal notranslate">inner</code> function because <code class="docutils literal notranslate">*args</code> and <code class="docutils literal notranslate">**kwargs</code> have to be typed <a class="reference internal" href="#typing.Any" title="typing.Any"><code class="xref py py-data docutils literal notranslate">Any</code></a>.</li> <li><a class="reference internal" href="#typing.cast" title="typing.cast"><code class="xref py py-func docutils literal notranslate">cast()</code></a> may be required in the body of the <code class="docutils literal notranslate">add_logging</code> decorator when returning the <code class="docutils literal notranslate">inner</code> function, or the static type checker must be told to ignore the <code class="docutils literal notranslate">return inner</code>.</li> </ol> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.ParamSpec.args"> args<a class="headerlink" href="#typing.ParamSpec.args" title="Link to this definition">¶</a></dt> <dd></dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.ParamSpec.kwargs"> kwargs<a class="headerlink" href="#typing.ParamSpec.kwargs" title="Link to this definition">¶</a></dt> <dd>Since <code class="docutils literal notranslate">ParamSpec</code> captures both positional and keyword parameters, <code class="docutils literal notranslate">P.args</code> and <code class="docutils literal notranslate">P.kwargs</code> can be used to split a <code class="docutils literal notranslate">ParamSpec</code> into its components. <code class="docutils literal notranslate">P.args</code> represents the tuple of positional parameters in a given call and should only be used to annotate <code class="docutils literal notranslate">*args</code>. <code class="docutils literal notranslate">P.kwargs</code> represents the mapping of keyword parameters to their values in a given call, and should be only be used to annotate <code class="docutils literal notranslate">**kwargs</code>. Both attributes require the annotated parameter to be in scope. At runtime, <code class="docutils literal notranslate">P.args</code> and <code class="docutils literal notranslate">P.kwargs</code> are instances respectively of <a class="reference internal" href="#typing.ParamSpecArgs" title="typing.ParamSpecArgs"><code class="xref py py-class docutils literal notranslate">ParamSpecArgs</code></a> and <a class="reference internal" href="#typing.ParamSpecKwargs" title="typing.ParamSpecKwargs"><code class="xref py py-class docutils literal notranslate">ParamSpecKwargs</code></a>. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.ParamSpec.__name__"> __name__<a class="headerlink" href="#typing.ParamSpec.__name__" title="Link to this definition">¶</a></dt> <dd>The name of the parameter specification. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.ParamSpec.__default__"> __default__<a class="headerlink" href="#typing.ParamSpec.__default__" title="Link to this definition">¶</a></dt> <dd>The default value of the parameter specification, or <a class="reference internal" href="#typing.NoDefault" title="typing.NoDefault"><code class="xref py py-data docutils literal notranslate">typing.NoDefault</code></a> if it has no default. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="typing.ParamSpec.has_default"> has_default()<a class="headerlink" href="#typing.ParamSpec.has_default" title="Link to this definition">¶</a></dt> <dd>Return whether or not the parameter specification has a default value. This is equivalent to checking whether <a class="reference internal" href="#typing.ParamSpec.__default__" title="typing.ParamSpec.__default__"><code class="xref py py-attr docutils literal notranslate">__default__</code></a> is not the <a class="reference internal" href="#typing.NoDefault" title="typing.NoDefault"><code class="xref py py-data docutils literal notranslate">typing.NoDefault</code></a> singleton, except that it does not force evaluation of the <a class="reference internal" href="../reference/executionmodel.html#lazy-evaluation">lazily evaluated</a> default value. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> Parameter specification variables created with <code class="docutils literal notranslate">covariant=True</code> or <code class="docutils literal notranslate">contravariant=True</code> can be used to declare covariant or contravariant generic types. The <code class="docutils literal notranslate">bound</code> argument is also accepted, similar to <a class="reference internal" href="#typing.TypeVar" title="typing.TypeVar"><code class="xref py py-class docutils literal notranslate">TypeVar</code></a>. However the actual semantics of these keywords are yet to be decided. <div class="versionadded"> Added in version 3.10. </div> <div class="versionchanged"> Changed in version 3.12: Parameter specifications can now be declared using the <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter</a> syntax introduced by <a class="pep reference external" href="https://peps.python.org/pep-0695/">PEP 695</a>. </div> <div class="versionchanged"> Changed in version 3.13: Support for default values was added. </div> <div class="admonition note"> Note Only parameter specification variables defined in global scope can be pickled. </div> <div class="admonition seealso"> See also <ul class="simple"> <li><a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a> – Parameter Specification Variables (the PEP which introduced <code class="docutils literal notranslate">ParamSpec</code> and <code class="docutils literal notranslate">Concatenate</code>)</li> <li><a class="reference internal" href="#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-data docutils literal notranslate">Concatenate</code></a></li> <li><a class="reference internal" href="#annotating-callables">Annotating callable objects</a></li> </ul> </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.ParamSpecArgs"> typing.ParamSpecArgs<a class="headerlink" href="#typing.ParamSpecArgs" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="typing.ParamSpecKwargs"> typing.ParamSpecKwargs<a class="headerlink" href="#typing.ParamSpecKwargs" title="Link to this definition">¶</a></dt> <dd>Arguments and keyword arguments attributes of a <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a>. The <code class="docutils literal notranslate">P.args</code> attribute of a <code class="docutils literal notranslate">ParamSpec</code> is an instance of <code class="docutils literal notranslate">ParamSpecArgs</code>, and <code class="docutils literal notranslate">P.kwargs</code> is an instance of <code class="docutils literal notranslate">ParamSpecKwargs</code>. They are intended for runtime introspection and have no special meaning to static type checkers. Calling <a class="reference internal" href="#typing.get_origin" title="typing.get_origin"><code class="xref py py-func docutils literal notranslate">get_origin()</code></a> on either of these objects will return the original <code class="docutils literal notranslate">ParamSpec</code>: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> from typing import ParamSpec, get_origin >>> P = ParamSpec("P") >>> get_origin(P.args) is P True >>> get_origin(P.kwargs) is P True </pre></div> </div> <div class="versionadded"> Added in version 3.10. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.TypeAliasType"> class typing.TypeAliasType(name, value, *, type_params=())<a class="headerlink" href="#typing.TypeAliasType" title="Link to this definition">¶</a></dt> <dd>The type of type aliases created through the <a class="reference internal" href="../reference/simple_stmts.html#type"><code class="xref std std-keyword docutils literal notranslate">type</code></a> statement. Example: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> type Alias = int >>> type(Alias) <class 'typing.TypeAliasType'> </pre></div> </div> <div class="versionadded"> Added in version 3.12. </div> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeAliasType.__name__"> __name__<a class="headerlink" href="#typing.TypeAliasType.__name__" title="Link to this definition">¶</a></dt> <dd>The name of the type alias: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> type Alias = int >>> Alias.__name__ 'Alias' </pre></div> </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeAliasType.__module__"> __module__<a class="headerlink" href="#typing.TypeAliasType.__module__" title="Link to this definition">¶</a></dt> <dd>The module in which the type alias was defined: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> type Alias = int >>> Alias.__module__ '__main__' </pre></div> </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeAliasType.__type_params__"> __type_params__<a class="headerlink" href="#typing.TypeAliasType.__type_params__" title="Link to this definition">¶</a></dt> <dd>The type parameters of the type alias, or an empty tuple if the alias is not generic: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> type ListOrSet[T] = list[T] | set[T] >>> ListOrSet.__type_params__ (T,) >>> type NotGeneric = int >>> NotGeneric.__type_params__ () </pre></div> </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypeAliasType.__value__"> __value__<a class="headerlink" href="#typing.TypeAliasType.__value__" title="Link to this definition">¶</a></dt> <dd>The type alias’s value. This is <a class="reference internal" href="../reference/executionmodel.html#lazy-evaluation">lazily evaluated</a>, so names used in the definition of the alias are not resolved until the <code class="docutils literal notranslate">__value__</code> attribute is accessed: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> type Mutually = Recursive >>> type Recursive = Mutually >>> Mutually Mutually >>> Recursive Recursive >>> Mutually.__value__ Recursive >>> Recursive.__value__ Mutually </pre></div> </div> </dd></dl> </dd></dl> </section> <section id="other-special-directives"> <h4>Other special directives<a class="headerlink" href="#other-special-directives" title="Link to this heading">¶</a></h4> These functions and classes should not be used directly as annotations. Their intended purpose is to be building blocks for creating and declaring types. <dl class="py class"> <dt class="sig sig-object py" id="typing.NamedTuple"> class typing.NamedTuple<a class="headerlink" href="#typing.NamedTuple" title="Link to this definition">¶</a></dt> <dd>Typed version of <a class="reference internal" href="collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-func docutils literal notranslate">collections.namedtuple()</code></a>. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Employee(NamedTuple): name: str id: int </pre></div> </div> This is equivalent to: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Employee = collections.namedtuple('Employee', ['name', 'id']) </pre></div> </div> To give a field a default value, you can assign to it in the class body: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Employee(NamedTuple): name: str id: int = 3 employee = Employee('Guido') assert employee.id == 3 </pre></div> </div> Fields with a default value must come after any fields without a default. The resulting class has an extra attribute <code class="docutils literal notranslate">__annotations__</code> giving a dict that maps the field names to the field types. (The field names are in the <code class="docutils literal notranslate">_fields</code> attribute and the default values are in the <code class="docutils literal notranslate">_field_defaults</code> attribute, both of which are part of the <a class="reference internal" href="collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-func docutils literal notranslate">namedtuple()</code></a> API.) <code class="docutils literal notranslate">NamedTuple</code> subclasses can also have docstrings and methods: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Employee(NamedTuple): """Represents an employee.""" name: str id: int = 3 def __repr__(self) -> str: return f'<Employee {self.name}, id={self.id}>' </pre></div> </div> <code class="docutils literal notranslate">NamedTuple</code> subclasses can be generic: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Group[T](NamedTuple): key: T group: list[T] </pre></div> </div> Backward-compatible usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre># For creating a generic NamedTuple on Python 3.11 T = TypeVar("T") class Group(NamedTuple, Generic[T]): key: T group: list[T] # A functional syntax is also supported Employee = NamedTuple('Employee', [('name', str), ('id', int)]) </pre></div> </div> <div class="versionchanged"> Changed in version 3.6: Added support for <a class="pep reference external" href="https://peps.python.org/pep-0526/">PEP 526</a> variable annotation syntax. </div> <div class="versionchanged"> Changed in version 3.6.1: Added support for default values, methods, and docstrings. </div> <div class="versionchanged"> Changed in version 3.8: The <code class="docutils literal notranslate">_field_types</code> and <code class="docutils literal notranslate">__annotations__</code> attributes are now regular dictionaries instead of instances of <code class="docutils literal notranslate">OrderedDict</code>. </div> <div class="versionchanged"> Changed in version 3.9: Removed the <code class="docutils literal notranslate">_field_types</code> attribute in favor of the more standard <code class="docutils literal notranslate">__annotations__</code> attribute which has the same information. </div> <div class="versionchanged"> Changed in version 3.11: Added support for generic namedtuples. </div> <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.15: The undocumented keyword argument syntax for creating NamedTuple classes (<code class="docutils literal notranslate">NT = NamedTuple("NT", x=int)</code>) is deprecated, and will be disallowed in 3.15. Use the class-based syntax or the functional syntax instead. </div> <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.15: When using the functional syntax to create a NamedTuple class, failing to pass a value to the ‘fields’ parameter (<code class="docutils literal notranslate">NT = NamedTuple("NT")</code>) is deprecated. Passing <code class="docutils literal notranslate">None</code> to the ‘fields’ parameter (<code class="docutils literal notranslate">NT = NamedTuple("NT", None)</code>) is also deprecated. Both will be disallowed in Python 3.15. To create a NamedTuple class with 0 fields, use <code class="docutils literal notranslate">class NT(NamedTuple): pass</code> or <code class="docutils literal notranslate">NT = NamedTuple("NT", [])</code>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.NewType"> class typing.NewType(name, tp)<a class="headerlink" href="#typing.NewType" title="Link to this definition">¶</a></dt> <dd>Helper class to create low-overhead <a class="reference internal" href="#distinct">distinct types</a>. A <code class="docutils literal notranslate">NewType</code> is considered a distinct type by a typechecker. At runtime, however, calling a <code class="docutils literal notranslate">NewType</code> returns its argument unchanged. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>UserId = NewType('UserId', int) # Declare the NewType "UserId" first_user = UserId(1) # "UserId" returns the argument unchanged at runtime </pre></div> </div> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.NewType.__module__"> __module__<a class="headerlink" href="#typing.NewType.__module__" title="Link to this definition">¶</a></dt> <dd>The module in which the new type is defined. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.NewType.__name__"> __name__<a class="headerlink" href="#typing.NewType.__name__" title="Link to this definition">¶</a></dt> <dd>The name of the new type. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.NewType.__supertype__"> __supertype__<a class="headerlink" href="#typing.NewType.__supertype__" title="Link to this definition">¶</a></dt> <dd>The type that the new type is based on. </dd></dl> <div class="versionadded"> Added in version 3.5.2. </div> <div class="versionchanged"> Changed in version 3.10: <code class="docutils literal notranslate">NewType</code> is now a class rather than a function. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Protocol"> class typing.Protocol(Generic)<a class="headerlink" href="#typing.Protocol" title="Link to this definition">¶</a></dt> <dd>Base class for protocol classes. Protocol classes are defined like this: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Proto(Protocol): def meth(self) -> int: ... </pre></div> </div> Such classes are primarily used with static type checkers that recognize structural subtyping (static duck-typing), for example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class C: def meth(self) -> int: return 0 def func(x: Proto) -> int: return x.meth() func(C()) # Passes static type check </pre></div> </div> See <a class="pep reference external" href="https://peps.python.org/pep-0544/">PEP 544</a> for more details. Protocol classes decorated with <a class="reference internal" href="#typing.runtime_checkable" title="typing.runtime_checkable"><code class="xref py py-func docutils literal notranslate">runtime_checkable()</code></a> (described later) act as simple-minded runtime protocols that check only the presence of given attributes, ignoring their type signatures. Protocol classes can be generic, for example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class GenProto[T](Protocol): def meth(self) -> T: ... </pre></div> </div> In code that needs to be compatible with Python 3.11 or older, generic Protocols can be written as follows: <div class="highlight-python3 notranslate"><div class="highlight"><pre>T = TypeVar("T") class GenProto(Protocol[T]): def meth(self) -> T: ... </pre></div> </div> <div class="versionadded"> Added in version 3.8. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.runtime_checkable"> @typing.runtime_checkable<a class="headerlink" href="#typing.runtime_checkable" title="Link to this definition">¶</a></dt> <dd>Mark a protocol class as a runtime protocol. Such a protocol can be used with <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> and <a class="reference internal" href="functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate">issubclass()</code></a>. This raises <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> when applied to a non-protocol class. This allows a simple-minded structural check, very similar to “one trick ponies” in <a class="reference internal" href="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> such as <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal notranslate">Iterable</code></a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>@runtime_checkable class Closable(Protocol): def close(self): ... assert isinstance(open('/some/file'), Closable) @runtime_checkable class Named(Protocol): name: str import threading assert isinstance(threading.Thread(name='Bob'), Named) </pre></div> </div> <div class="admonition note"> Note <code class="xref py py-func docutils literal notranslate">runtime_checkable()</code> will check only the presence of the required methods or attributes, not their type signatures or types. For example, <a class="reference internal" href="ssl.html#ssl.SSLObject" title="ssl.SSLObject"><code class="xref py py-class docutils literal notranslate">ssl.SSLObject</code></a> is a class, therefore it passes an <a class="reference internal" href="functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate">issubclass()</code></a> check against <a class="reference internal" href="#annotating-callables">Callable</a>. However, the <code class="docutils literal notranslate">ssl.SSLObject.__init__</code> method exists only to raise a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> with a more informative message, therefore making it impossible to call (instantiate) <a class="reference internal" href="ssl.html#ssl.SSLObject" title="ssl.SSLObject"><code class="xref py py-class docutils literal notranslate">ssl.SSLObject</code></a>. </div> <div class="admonition note"> Note An <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> check against a runtime-checkable protocol can be surprisingly slow compared to an <code class="docutils literal notranslate">isinstance()</code> check against a non-protocol class. Consider using alternative idioms such as <a class="reference internal" href="functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate">hasattr()</code></a> calls for structural checks in performance-sensitive code. </div> <div class="versionadded"> Added in version 3.8. </div> <div class="versionchanged"> Changed in version 3.12: The internal implementation of <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> checks against runtime-checkable protocols now uses <a class="reference internal" href="inspect.html#inspect.getattr_static" title="inspect.getattr_static"><code class="xref py py-func docutils literal notranslate">inspect.getattr_static()</code></a> to look up attributes (previously, <a class="reference internal" href="functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate">hasattr()</code></a> was used). As a result, some objects which used to be considered instances of a runtime-checkable protocol may no longer be considered instances of that protocol on Python 3.12+, and vice versa. Most users are unlikely to be affected by this change. </div> <div class="versionchanged"> Changed in version 3.12: The members of a runtime-checkable protocol are now considered “frozen” at runtime as soon as the class has been created. Monkey-patching attributes onto a runtime-checkable protocol will still work, but will have no impact on <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> checks comparing objects to the protocol. See <a class="reference internal" href="../whatsnew/3.12.html#whatsnew-typing-py312">“What’s new in Python 3.12”</a> for more details. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.TypedDict"> class typing.TypedDict(dict)<a class="headerlink" href="#typing.TypedDict" title="Link to this definition">¶</a></dt> <dd>Special construct to add type hints to a dictionary. At runtime it is a plain <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>. <code class="docutils literal notranslate">TypedDict</code> declares a dictionary type that expects all of its instances to have a certain set of keys, where each key is associated with a value of a consistent type. This expectation is not checked at runtime but is only enforced by type checkers. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point2D(TypedDict): x: int y: int label: str a: Point2D = {'x': 1, 'y': 2, 'label': 'good'} # OK b: Point2D = {'z': 3, 'label': 'bad'} # Fails type check assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first') </pre></div> </div> An alternative way to create a <code class="docutils literal notranslate">TypedDict</code> is by using function-call syntax. The second argument must be a literal <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str}) </pre></div> </div> This functional syntax allows defining keys which are not valid <a class="reference internal" href="../reference/lexical_analysis.html#identifiers">identifiers</a>, for example because they are keywords or contain hyphens: <div class="highlight-python3 notranslate"><div class="highlight"><pre># raises SyntaxError class Point2D(TypedDict): in: int # 'in' is a keyword x-y: int # name with hyphens # OK, functional syntax Point2D = TypedDict('Point2D', {'in': int, 'x-y': int}) </pre></div> </div> By default, all keys must be present in a <code class="docutils literal notranslate">TypedDict</code>. It is possible to mark individual keys as non-required using <a class="reference internal" href="#typing.NotRequired" title="typing.NotRequired"><code class="xref py py-data docutils literal notranslate">NotRequired</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point2D(TypedDict): x: int y: int label: NotRequired[str] # Alternative syntax Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': NotRequired[str]}) </pre></div> </div> This means that a <code class="docutils literal notranslate">Point2D</code> <code class="docutils literal notranslate">TypedDict</code> can have the <code class="docutils literal notranslate">label</code> key omitted. It is also possible to mark all keys as non-required by default by specifying a totality of <code class="docutils literal notranslate">False</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point2D(TypedDict, total=False): x: int y: int # Alternative syntax Point2D = TypedDict('Point2D', {'x': int, 'y': int}, total=False) </pre></div> </div> This means that a <code class="docutils literal notranslate">Point2D</code> <code class="docutils literal notranslate">TypedDict</code> can have any of the keys omitted. A type checker is only expected to support a literal <code class="docutils literal notranslate">False</code> or <code class="docutils literal notranslate">True</code> as the value of the <code class="docutils literal notranslate">total</code> argument. <code class="docutils literal notranslate">True</code> is the default, and makes all items defined in the class body required. Individual keys of a <code class="docutils literal notranslate">total=False</code> <code class="docutils literal notranslate">TypedDict</code> can be marked as required using <a class="reference internal" href="#typing.Required" title="typing.Required"><code class="xref py py-data docutils literal notranslate">Required</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point2D(TypedDict, total=False): x: Required[int] y: Required[int] label: str # Alternative syntax Point2D = TypedDict('Point2D', { 'x': Required[int], 'y': Required[int], 'label': str }, total=False) </pre></div> </div> It is possible for a <code class="docutils literal notranslate">TypedDict</code> type to inherit from one or more other <code class="docutils literal notranslate">TypedDict</code> types using the class-based syntax. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point3D(Point2D): z: int </pre></div> </div> <code class="docutils literal notranslate">Point3D</code> has three items: <code class="docutils literal notranslate">x</code>, <code class="docutils literal notranslate">y</code> and <code class="docutils literal notranslate">z</code>. It is equivalent to this definition: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point3D(TypedDict): x: int y: int z: int </pre></div> </div> A <code class="docutils literal notranslate">TypedDict</code> cannot inherit from a non-<code class="docutils literal notranslate">TypedDict</code> class, except for <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class X(TypedDict): x: int class Y(TypedDict): y: int class Z(object): pass # A non-TypedDict class class XY(X, Y): pass # OK class XZ(X, Z): pass # raises TypeError </pre></div> </div> A <code class="docutils literal notranslate">TypedDict</code> can be generic: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Group[T](TypedDict): key: T group: list[T] </pre></div> </div> To create a generic <code class="docutils literal notranslate">TypedDict</code> that is compatible with Python 3.11 or lower, inherit from <a class="reference internal" href="#typing.Generic" title="typing.Generic"><code class="xref py py-class docutils literal notranslate">Generic</code></a> explicitly: <div class="highlight-python notranslate"><div class="highlight"><pre>T = TypeVar("T") class Group(TypedDict, Generic[T]): key: T group: list[T] </pre></div> </div> A <code class="docutils literal notranslate">TypedDict</code> can be introspected via annotations dicts (see <a class="reference internal" href="../howto/annotations.html#annotations-howto">Annotations Best Practices</a> for more information on annotations best practices), <a class="reference internal" href="#typing.TypedDict.__total__" title="typing.TypedDict.__total__"><code class="xref py py-attr docutils literal notranslate">__total__</code></a>, <a class="reference internal" href="#typing.TypedDict.__required_keys__" title="typing.TypedDict.__required_keys__"><code class="xref py py-attr docutils literal notranslate">__required_keys__</code></a>, and <a class="reference internal" href="#typing.TypedDict.__optional_keys__" title="typing.TypedDict.__optional_keys__"><code class="xref py py-attr docutils literal notranslate">__optional_keys__</code></a>. <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypedDict.__total__"> __total__<a class="headerlink" href="#typing.TypedDict.__total__" title="Link to this definition">¶</a></dt> <dd><code class="docutils literal notranslate">Point2D.__total__</code> gives the value of the <code class="docutils literal notranslate">total</code> argument. Example: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> from typing import TypedDict >>> class Point2D(TypedDict): pass >>> Point2D.__total__ True >>> class Point2D(TypedDict, total=False): pass >>> Point2D.__total__ False >>> class Point3D(Point2D): pass >>> Point3D.__total__ True </pre></div> </div> This attribute reflects only the value of the <code class="docutils literal notranslate">total</code> argument to the current <code class="docutils literal notranslate">TypedDict</code> class, not whether the class is semantically total. For example, a <code class="docutils literal notranslate">TypedDict</code> with <code class="docutils literal notranslate">__total__</code> set to <code class="docutils literal notranslate">True</code> may have keys marked with <a class="reference internal" href="#typing.NotRequired" title="typing.NotRequired"><code class="xref py py-data docutils literal notranslate">NotRequired</code></a>, or it may inherit from another <code class="docutils literal notranslate">TypedDict</code> with <code class="docutils literal notranslate">total=False</code>. Therefore, it is generally better to use <a class="reference internal" href="#typing.TypedDict.__required_keys__" title="typing.TypedDict.__required_keys__"><code class="xref py py-attr docutils literal notranslate">__required_keys__</code></a> and <a class="reference internal" href="#typing.TypedDict.__optional_keys__" title="typing.TypedDict.__optional_keys__"><code class="xref py py-attr docutils literal notranslate">__optional_keys__</code></a> for introspection. </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypedDict.__required_keys__"> __required_keys__<a class="headerlink" href="#typing.TypedDict.__required_keys__" title="Link to this definition">¶</a></dt> <dd><div class="versionadded"> Added in version 3.9. </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypedDict.__optional_keys__"> __optional_keys__<a class="headerlink" href="#typing.TypedDict.__optional_keys__" title="Link to this definition">¶</a></dt> <dd><code class="docutils literal notranslate">Point2D.__required_keys__</code> and <code class="docutils literal notranslate">Point2D.__optional_keys__</code> return <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a> objects containing required and non-required keys, respectively. Keys marked with <a class="reference internal" href="#typing.Required" title="typing.Required"><code class="xref py py-data docutils literal notranslate">Required</code></a> will always appear in <code class="docutils literal notranslate">__required_keys__</code> and keys marked with <a class="reference internal" href="#typing.NotRequired" title="typing.NotRequired"><code class="xref py py-data docutils literal notranslate">NotRequired</code></a> will always appear in <code class="docutils literal notranslate">__optional_keys__</code>. For backwards compatibility with Python 3.10 and below, it is also possible to use inheritance to declare both required and non-required keys in the same <code class="docutils literal notranslate">TypedDict</code> . This is done by declaring a <code class="docutils literal notranslate">TypedDict</code> with one value for the <code class="docutils literal notranslate">total</code> argument and then inheriting from it in another <code class="docutils literal notranslate">TypedDict</code> with a different value for <code class="docutils literal notranslate">total</code>: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> class Point2D(TypedDict, total=False): ... x: int ... y: int ... >>> class Point3D(Point2D): ... z: int ... >>> Point3D.__required_keys__ == frozenset({'z'}) True >>> Point3D.__optional_keys__ == frozenset({'x', 'y'}) True </pre></div> </div> <div class="versionadded"> Added in version 3.9. </div> <div class="admonition note"> Note If <code class="docutils literal notranslate">from __future__ import annotations</code> is used or if annotations are given as strings, annotations are not evaluated when the <code class="docutils literal notranslate">TypedDict</code> is defined. Therefore, the runtime introspection that <code class="docutils literal notranslate">__required_keys__</code> and <code class="docutils literal notranslate">__optional_keys__</code> rely on may not work properly, and the values of the attributes may be incorrect. </div> </dd></dl> Support for <a class="reference internal" href="#typing.ReadOnly" title="typing.ReadOnly"><code class="xref py py-data docutils literal notranslate">ReadOnly</code></a> is reflected in the following attributes: <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypedDict.__readonly_keys__"> __readonly_keys__<a class="headerlink" href="#typing.TypedDict.__readonly_keys__" title="Link to this definition">¶</a></dt> <dd>A <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a> containing the names of all read-only keys. Keys are read-only if they carry the <a class="reference internal" href="#typing.ReadOnly" title="typing.ReadOnly"><code class="xref py py-data docutils literal notranslate">ReadOnly</code></a> qualifier. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py attribute"> <dt class="sig sig-object py" id="typing.TypedDict.__mutable_keys__"> __mutable_keys__<a class="headerlink" href="#typing.TypedDict.__mutable_keys__" title="Link to this definition">¶</a></dt> <dd>A <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">frozenset</code></a> containing the names of all mutable keys. Keys are mutable if they do not carry the <a class="reference internal" href="#typing.ReadOnly" title="typing.ReadOnly"><code class="xref py py-data docutils literal notranslate">ReadOnly</code></a> qualifier. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> See <a class="pep reference external" href="https://peps.python.org/pep-0589/">PEP 589</a> for more examples and detailed rules of using <code class="docutils literal notranslate">TypedDict</code>. <div class="versionadded"> Added in version 3.8. </div> <div class="versionchanged"> Changed in version 3.11: Added support for marking individual keys as <a class="reference internal" href="#typing.Required" title="typing.Required"><code class="xref py py-data docutils literal notranslate">Required</code></a> or <a class="reference internal" href="#typing.NotRequired" title="typing.NotRequired"><code class="xref py py-data docutils literal notranslate">NotRequired</code></a>. See <a class="pep reference external" href="https://peps.python.org/pep-0655/">PEP 655</a>. </div> <div class="versionchanged"> Changed in version 3.11: Added support for generic <code class="docutils literal notranslate">TypedDict</code>s. </div> <div class="versionchanged"> Changed in version 3.13: Removed support for the keyword-argument method of creating <code class="docutils literal notranslate">TypedDict</code>s. </div> <div class="versionchanged"> Changed in version 3.13: Support for the <a class="reference internal" href="#typing.ReadOnly" title="typing.ReadOnly"><code class="xref py py-data docutils literal notranslate">ReadOnly</code></a> qualifier was added. </div> <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.15: When using the functional syntax to create a TypedDict class, failing to pass a value to the ‘fields’ parameter (<code class="docutils literal notranslate">TD = TypedDict("TD")</code>) is deprecated. Passing <code class="docutils literal notranslate">None</code> to the ‘fields’ parameter (<code class="docutils literal notranslate">TD = TypedDict("TD", None)</code>) is also deprecated. Both will be disallowed in Python 3.15. To create a TypedDict class with 0 fields, use <code class="docutils literal notranslate">class TD(TypedDict): pass</code> or <code class="docutils literal notranslate">TD = TypedDict("TD", {})</code>. </div> </dd></dl> </section> </section> <section id="protocols"> <h3>Protocols<a class="headerlink" href="#protocols" title="Link to this heading">¶</a></h3> The following protocols are provided by the typing module. All are decorated with <a class="reference internal" href="#typing.runtime_checkable" title="typing.runtime_checkable"><code class="xref py py-func docutils literal notranslate">@runtime_checkable</code></a>. <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsAbs"> class typing.SupportsAbs<a class="headerlink" href="#typing.SupportsAbs" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__abs__</code> that is covariant in its return type. </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsBytes"> class typing.SupportsBytes<a class="headerlink" href="#typing.SupportsBytes" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__bytes__</code>. </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsComplex"> class typing.SupportsComplex<a class="headerlink" href="#typing.SupportsComplex" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__complex__</code>. </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsFloat"> class typing.SupportsFloat<a class="headerlink" href="#typing.SupportsFloat" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__float__</code>. </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsIndex"> class typing.SupportsIndex<a class="headerlink" href="#typing.SupportsIndex" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__index__</code>. <div class="versionadded"> Added in version 3.8. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsInt"> class typing.SupportsInt<a class="headerlink" href="#typing.SupportsInt" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__int__</code>. </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.SupportsRound"> class typing.SupportsRound<a class="headerlink" href="#typing.SupportsRound" title="Link to this definition">¶</a></dt> <dd>An ABC with one abstract method <code class="docutils literal notranslate">__round__</code> that is covariant in its return type. </dd></dl> </section> <section id="abcs-for-working-with-io"> <h3>ABCs for working with IO<a class="headerlink" href="#abcs-for-working-with-io" title="Link to this heading">¶</a></h3> <dl class="py class"> <dt class="sig sig-object py" id="typing.IO"> class typing.IO<a class="headerlink" href="#typing.IO" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="typing.TextIO"> class typing.TextIO<a class="headerlink" href="#typing.TextIO" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="typing.BinaryIO"> class typing.BinaryIO<a class="headerlink" href="#typing.BinaryIO" title="Link to this definition">¶</a></dt> <dd>Generic type <code class="docutils literal notranslate">IO[AnyStr]</code> and its subclasses <code class="docutils literal notranslate">TextIO(IO[str])</code> and <code class="docutils literal notranslate">BinaryIO(IO[bytes])</code> represent the types of I/O streams such as returned by <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a>. </dd></dl> </section> <section id="functions-and-decorators"> <h3>Functions and decorators<a class="headerlink" href="#functions-and-decorators" title="Link to this heading">¶</a></h3> <dl class="py function"> <dt class="sig sig-object py" id="typing.cast"> typing.cast(typ, val)<a class="headerlink" href="#typing.cast" title="Link to this definition">¶</a></dt> <dd>Cast a value to a type. This returns the value unchanged. To the type checker this signals that the return value has the designated type, but at runtime we intentionally don’t check anything (we want this to be as fast as possible). </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.assert_type"> typing.assert_type(val, typ, /)<a class="headerlink" href="#typing.assert_type" title="Link to this definition">¶</a></dt> <dd>Ask a static type checker to confirm that val has an inferred type of typ. At runtime this does nothing: it returns the first argument unchanged with no checks or side effects, no matter the actual type of the argument. When a static type checker encounters a call to <code class="docutils literal notranslate">assert_type()</code>, it emits an error if the value is not of the specified type: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def greet(name: str) -> None: assert_type(name, str) # OK, inferred type of `name` is `str` assert_type(name, int) # type checker error </pre></div> </div> This function is useful for ensuring the type checker’s understanding of a script is in line with the developer’s intentions: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def complex_function(arg: object): # Do some complex type-narrowing logic, # after which we hope the inferred type will be `int` ... # Test whether the type checker correctly understands our function assert_type(arg, int) </pre></div> </div> <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.assert_never"> typing.assert_never(arg, /)<a class="headerlink" href="#typing.assert_never" title="Link to this definition">¶</a></dt> <dd>Ask a static type checker to confirm that a line of code is unreachable. Example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def int_or_str(arg: int | str) -> None: match arg: case int(): print("It's an int") case str(): print("It's a str") case _ as unreachable: assert_never(unreachable) </pre></div> </div> Here, the annotations allow the type checker to infer that the last case can never execute, because <code class="docutils literal notranslate">arg</code> is either an <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> or a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, and both options are covered by earlier cases. If a type checker finds that a call to <code class="docutils literal notranslate">assert_never()</code> is reachable, it will emit an error. For example, if the type annotation for <code class="docutils literal notranslate">arg</code> was instead <code class="docutils literal notranslate">int | str | float</code>, the type checker would emit an error pointing out that <code class="docutils literal notranslate">unreachable</code> is of type <a class="reference internal" href="functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate">float</code></a>. For a call to <code class="docutils literal notranslate">assert_never</code> to pass type checking, the inferred type of the argument passed in must be the bottom type, <a class="reference internal" href="#typing.Never" title="typing.Never"><code class="xref py py-data docutils literal notranslate">Never</code></a>, and nothing else. At runtime, this throws an exception when called. <div class="admonition seealso"> See also <a class="reference external" href="https://typing.readthedocs.io/en/latest/guides/unreachable.html">Unreachable Code and Exhaustiveness Checking</a> has more information about exhaustiveness checking with static typing. </div> <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.reveal_type"> typing.reveal_type(obj, /)<a class="headerlink" href="#typing.reveal_type" title="Link to this definition">¶</a></dt> <dd>Ask a static type checker to reveal the inferred type of an expression. When a static type checker encounters a call to this function, it emits a diagnostic with the inferred type of the argument. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>x: int = 1 reveal_type(x) # Revealed type is "builtins.int" </pre></div> </div> This can be useful when you want to debug how your type checker handles a particular piece of code. At runtime, this function prints the runtime type of its argument to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a> and returns the argument unchanged (allowing the call to be used within an expression): <div class="highlight-python3 notranslate"><div class="highlight"><pre>x = reveal_type(1) # prints "Runtime type is int" print(x) # prints "1" </pre></div> </div> Note that the runtime type may be different from (more or less specific than) the type statically inferred by a type checker. Most type checkers support <code class="docutils literal notranslate">reveal_type()</code> anywhere, even if the name is not imported from <code class="docutils literal notranslate">typing</code>. Importing the name from <code class="docutils literal notranslate">typing</code>, however, allows your code to run without runtime errors and communicates intent more clearly. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.dataclass_transform"> @typing.dataclass_transform(*, eq_default=True, order_default=False, kw_only_default=False, frozen_default=False, field_specifiers=(), **kwargs)<a class="headerlink" href="#typing.dataclass_transform" title="Link to this definition">¶</a></dt> <dd>Decorator to mark an object as providing <a class="reference internal" href="dataclasses.html#dataclasses.dataclass" title="dataclasses.dataclass"><code class="xref py py-func docutils literal notranslate">dataclass</code></a>-like behavior. <code class="docutils literal notranslate">dataclass_transform</code> may be used to decorate a class, metaclass, or a function that is itself a decorator. The presence of <code class="docutils literal notranslate">@dataclass_transform()</code> tells a static type checker that the decorated object performs runtime “magic” that transforms a class in a similar way to <a class="reference internal" href="dataclasses.html#dataclasses.dataclass" title="dataclasses.dataclass"><code class="xref py py-func docutils literal notranslate">@dataclasses.dataclass</code></a>. Example usage with a decorator function: <div class="highlight-python notranslate"><div class="highlight"><pre>@dataclass_transform() def create_model[T](cls: type[T]) -> type[T]: ... return cls @create_model class CustomerModel: id: int name: str </pre></div> </div> On a base class: <div class="highlight-python3 notranslate"><div class="highlight"><pre>@dataclass_transform() class ModelBase: ... class CustomerModel(ModelBase): id: int name: str </pre></div> </div> On a metaclass: <div class="highlight-python3 notranslate"><div class="highlight"><pre>@dataclass_transform() class ModelMeta(type): ... class ModelBase(metaclass=ModelMeta): ... class CustomerModel(ModelBase): id: int name: str </pre></div> </div> The <code class="docutils literal notranslate">CustomerModel</code> classes defined above will be treated by type checkers similarly to classes created with <a class="reference internal" href="dataclasses.html#dataclasses.dataclass" title="dataclasses.dataclass"><code class="xref py py-func docutils literal notranslate">@dataclasses.dataclass</code></a>. For example, type checkers will assume these classes have <code class="docutils literal notranslate">__init__</code> methods that accept <code class="docutils literal notranslate">id</code> and <code class="docutils literal notranslate">name</code>. The decorated class, metaclass, or function may accept the following bool arguments which type checkers will assume have the same effect as they would have on the <a class="reference internal" href="dataclasses.html#dataclasses.dataclass" title="dataclasses.dataclass"><code class="xref py py-func docutils literal notranslate">@dataclasses.dataclass</code></a> decorator: <code class="docutils literal notranslate">init</code>, <code class="docutils literal notranslate">eq</code>, <code class="docutils literal notranslate">order</code>, <code class="docutils literal notranslate">unsafe_hash</code>, <code class="docutils literal notranslate">frozen</code>, <code class="docutils literal notranslate">match_args</code>, <code class="docutils literal notranslate">kw_only</code>, and <code class="docutils literal notranslate">slots</code>. It must be possible for the value of these arguments (<code class="docutils literal notranslate">True</code> or <code class="docutils literal notranslate">False</code>) to be statically evaluated. The arguments to the <code class="docutils literal notranslate">dataclass_transform</code> decorator can be used to customize the default behaviors of the decorated class, metaclass, or function: <dl class="field-list simple"> <dt class="field-odd">Parameters:</dt> <dd class="field-odd"><ul class="simple"> <li>eq_default (<a class="reference internal" href="functions.html#bool" title="bool">bool</a>) – Indicates whether the <code class="docutils literal notranslate">eq</code> parameter is assumed to be <code class="docutils literal notranslate">True</code> or <code class="docutils literal notranslate">False</code> if it is omitted by the caller. Defaults to <code class="docutils literal notranslate">True</code>.</li> <li>order_default (<a class="reference internal" href="functions.html#bool" title="bool">bool</a>) – Indicates whether the <code class="docutils literal notranslate">order</code> parameter is assumed to be <code class="docutils literal notranslate">True</code> or <code class="docutils literal notranslate">False</code> if it is omitted by the caller. Defaults to <code class="docutils literal notranslate">False</code>.</li> <li>kw_only_default (<a class="reference internal" href="functions.html#bool" title="bool">bool</a>) – Indicates whether the <code class="docutils literal notranslate">kw_only</code> parameter is assumed to be <code class="docutils literal notranslate">True</code> or <code class="docutils literal notranslate">False</code> if it is omitted by the caller. Defaults to <code class="docutils literal notranslate">False</code>.</li> <li>frozen_default (<a class="reference internal" href="functions.html#bool" title="bool">bool</a>) – Indicates whether the <code class="docutils literal notranslate">frozen</code> parameter is assumed to be <code class="docutils literal notranslate">True</code> or <code class="docutils literal notranslate">False</code> if it is omitted by the caller. Defaults to <code class="docutils literal notranslate">False</code>. <div class="versionadded"> Added in version 3.12. </div> </li> <li>field_specifiers (<a class="reference internal" href="stdtypes.html#tuple" title="tuple">tuple</a>[<a class="reference internal" href="collections.abc.html#collections.abc.Callable" title="collections.abc.Callable">Callable</a>[..., Any], ...]) – Specifies a static list of supported classes or functions that describe fields, similar to <a class="reference internal" href="dataclasses.html#dataclasses.field" title="dataclasses.field"><code class="xref py py-func docutils literal notranslate">dataclasses.field()</code></a>. Defaults to <code class="docutils literal notranslate">()</code>.</li> <li>**kwargs (Any) – Arbitrary other keyword arguments are accepted in order to allow for possible future extensions.</li> </ul> </dd> </dl> Type checkers recognize the following optional parameters on field specifiers: <table class="docutils align-default" id="id7"> <caption>Recognised parameters for field specifiers<a class="headerlink" href="#id7" title="Link to this table">¶</a></caption> <colgroup> <col style="width: 20.0%" /> <col style="width: 80.0%" /> </colgroup> <thead> <tr class="row-odd"><th class="head">Parameter name</th> <th class="head">Description</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">init</code></td> <td>Indicates whether the field should be included in the synthesized <code class="docutils literal notranslate">__init__</code> method. If unspecified, <code class="docutils literal notranslate">init</code> defaults to <code class="docutils literal notranslate">True</code>.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">default</code></td> <td>Provides the default value for the field.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">default_factory</code></td> <td>Provides a runtime callback that returns the default value for the field. If neither <code class="docutils literal notranslate">default</code> nor <code class="docutils literal notranslate">default_factory</code> are specified, the field is assumed to have no default value and must be provided a value when the class is instantiated.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">factory</code></td> <td>An alias for the <code class="docutils literal notranslate">default_factory</code> parameter on field specifiers.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">kw_only</code></td> <td>Indicates whether the field should be marked as keyword-only. If <code class="docutils literal notranslate">True</code>, the field will be keyword-only. If <code class="docutils literal notranslate">False</code>, it will not be keyword-only. If unspecified, the value of the <code class="docutils literal notranslate">kw_only</code> parameter on the object decorated with <code class="docutils literal notranslate">dataclass_transform</code> will be used, or if that is unspecified, the value of <code class="docutils literal notranslate">kw_only_default</code> on <code class="docutils literal notranslate">dataclass_transform</code> will be used.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">alias</code></td> <td>Provides an alternative name for the field. This alternative name is used in the synthesized <code class="docutils literal notranslate">__init__</code> method.</td> </tr> </tbody> </table> At runtime, this decorator records its arguments in the <code class="docutils literal notranslate">__dataclass_transform__</code> attribute on the decorated object. It has no other runtime effect. See <a class="pep reference external" href="https://peps.python.org/pep-0681/">PEP 681</a> for more details. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py function" id="overload"> <dt class="sig sig-object py" id="typing.overload"> @typing.overload<a class="headerlink" href="#typing.overload" title="Link to this definition">¶</a></dt> <dd>Decorator for creating overloaded functions and methods. The <code class="docutils literal notranslate">@overload</code> decorator allows describing functions and methods that support multiple different combinations of argument types. A series of <code class="docutils literal notranslate">@overload</code>-decorated definitions must be followed by exactly one non-<code class="docutils literal notranslate">@overload</code>-decorated definition (for the same function/method). <code class="docutils literal notranslate">@overload</code>-decorated definitions are for the benefit of the type checker only, since they will be overwritten by the non-<code class="docutils literal notranslate">@overload</code>-decorated definition. The non-<code class="docutils literal notranslate">@overload</code>-decorated definition, meanwhile, will be used at runtime but should be ignored by a type checker. At runtime, calling an <code class="docutils literal notranslate">@overload</code>-decorated function directly will raise <a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal notranslate">NotImplementedError</code></a>. An example of overload that gives a more precise type than can be expressed using a union or a type variable: <div class="highlight-python notranslate"><div class="highlight"><pre>@overload def process(response: None) -> None: ... @overload def process(response: int) -> tuple[int, str]: ... @overload def process(response: bytes) -> str: ... def process(response): ... # actual implementation goes here </pre></div> </div> See <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> for more details and comparison with other typing semantics. <div class="versionchanged"> Changed in version 3.11: Overloaded functions can now be introspected at runtime using <a class="reference internal" href="#typing.get_overloads" title="typing.get_overloads"><code class="xref py py-func docutils literal notranslate">get_overloads()</code></a>. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.get_overloads"> typing.get_overloads(func)<a class="headerlink" href="#typing.get_overloads" title="Link to this definition">¶</a></dt> <dd>Return a sequence of <a class="reference internal" href="#typing.overload" title="typing.overload"><code class="xref py py-func docutils literal notranslate">@overload</code></a>-decorated definitions for func. func is the function object for the implementation of the overloaded function. For example, given the definition of <code class="docutils literal notranslate">process</code> in the documentation for <a class="reference internal" href="#typing.overload" title="typing.overload"><code class="xref py py-func docutils literal notranslate">@overload</code></a>, <code class="docutils literal notranslate">get_overloads(process)</code> will return a sequence of three function objects for the three defined overloads. If called on a function with no overloads, <code class="docutils literal notranslate">get_overloads()</code> returns an empty sequence. <code class="docutils literal notranslate">get_overloads()</code> can be used for introspecting an overloaded function at runtime. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.clear_overloads"> typing.clear_overloads()<a class="headerlink" href="#typing.clear_overloads" title="Link to this definition">¶</a></dt> <dd>Clear all registered overloads in the internal registry. This can be used to reclaim the memory used by the registry. <div class="versionadded"> Added in version 3.11. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.final"> @typing.final<a class="headerlink" href="#typing.final" title="Link to this definition">¶</a></dt> <dd>Decorator to indicate final methods and final classes. Decorating a method with <code class="docutils literal notranslate">@final</code> indicates to a type checker that the method cannot be overridden in a subclass. Decorating a class with <code class="docutils literal notranslate">@final</code> indicates that it cannot be subclassed. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class Base: @final def done(self) -> None: ... class Sub(Base): def done(self) -> None: # Error reported by type checker ... @final class Leaf: ... class Other(Leaf): # Error reported by type checker ... </pre></div> </div> There is no runtime checking of these properties. See <a class="pep reference external" href="https://peps.python.org/pep-0591/">PEP 591</a> for more details. <div class="versionadded"> Added in version 3.8. </div> <div class="versionchanged"> Changed in version 3.11: The decorator will now attempt to set a <code class="docutils literal notranslate">__final__</code> attribute to <code class="docutils literal notranslate">True</code> on the decorated object. Thus, a check like <code class="docutils literal notranslate">if getattr(obj, "__final__", False)</code> can be used at runtime to determine whether an object <code class="docutils literal notranslate">obj</code> has been marked as final. If the decorated object does not support setting attributes, the decorator returns the object unchanged without raising an exception. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.no_type_check"> @typing.no_type_check<a class="headerlink" href="#typing.no_type_check" title="Link to this definition">¶</a></dt> <dd>Decorator to indicate that annotations are not type hints. This works as a class or function <a class="reference internal" href="../glossary.html#term-decorator">decorator</a>. With a class, it applies recursively to all methods and classes defined in that class (but not to methods defined in its superclasses or subclasses). Type checkers will ignore all annotations in a function or class with this decorator. <code class="docutils literal notranslate">@no_type_check</code> mutates the decorated object in place. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.no_type_check_decorator"> @typing.no_type_check_decorator<a class="headerlink" href="#typing.no_type_check_decorator" title="Link to this definition">¶</a></dt> <dd>Decorator to give another decorator the <a class="reference internal" href="#typing.no_type_check" title="typing.no_type_check"><code class="xref py py-func docutils literal notranslate">no_type_check()</code></a> effect. This wraps the decorator with something that wraps the decorated function in <a class="reference internal" href="#typing.no_type_check" title="typing.no_type_check"><code class="xref py py-func docutils literal notranslate">no_type_check()</code></a>. <div class="deprecated-removed"> Deprecated since version 3.13, will be removed in version 3.15: No type checker ever added support for <code class="docutils literal notranslate">@no_type_check_decorator</code>. It is therefore deprecated, and will be removed in Python 3.15. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.override"> @typing.override<a class="headerlink" href="#typing.override" title="Link to this definition">¶</a></dt> <dd>Decorator to indicate that a method in a subclass is intended to override a method or attribute in a superclass. Type checkers should emit an error if a method decorated with <code class="docutils literal notranslate">@override</code> does not, in fact, override anything. This helps prevent bugs that may occur when a base class is changed without an equivalent change to a child class. For example: <div class="highlight-python notranslate"><div class="highlight"><pre>class Base: def log_status(self) -> None: ... class Sub(Base): @override def log_status(self) -> None: # Okay: overrides Base.log_status ... @override def done(self) -> None: # Error reported by type checker ... </pre></div> </div> There is no runtime checking of this property. The decorator will attempt to set an <code class="docutils literal notranslate">__override__</code> attribute to <code class="docutils literal notranslate">True</code> on the decorated object. Thus, a check like <code class="docutils literal notranslate">if getattr(obj, "__override__", False)</code> can be used at runtime to determine whether an object <code class="docutils literal notranslate">obj</code> has been marked as an override. If the decorated object does not support setting attributes, the decorator returns the object unchanged without raising an exception. See <a class="pep reference external" href="https://peps.python.org/pep-0698/">PEP 698</a> for more details. <div class="versionadded"> Added in version 3.12. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.type_check_only"> @typing.type_check_only<a class="headerlink" href="#typing.type_check_only" title="Link to this definition">¶</a></dt> <dd>Decorator to mark a class or function as unavailable at runtime. This decorator is itself not available at runtime. It is mainly intended to mark classes that are defined in type stub files if an implementation returns an instance of a private class: <div class="highlight-python3 notranslate"><div class="highlight"><pre>@type_check_only class Response: # private or not available at runtime code: int def get_header(self, name: str) -> str: ... def fetch_response() -> Response: ... </pre></div> </div> Note that returning instances of private classes is not recommended. It is usually preferable to make such classes public. </dd></dl> </section> <section id="introspection-helpers"> <h3>Introspection helpers<a class="headerlink" href="#introspection-helpers" title="Link to this heading">¶</a></h3> <dl class="py function"> <dt class="sig sig-object py" id="typing.get_type_hints"> typing.get_type_hints(obj, globalns=None, localns=None, include_extras=False)<a class="headerlink" href="#typing.get_type_hints" title="Link to this definition">¶</a></dt> <dd>Return a dictionary containing type hints for a function, method, module or class object. This is often the same as <code class="docutils literal notranslate">obj.__annotations__</code>, but this function makes the following changes to the annotations dictionary: <ul class="simple"> <li>Forward references encoded as string literals or <a class="reference internal" href="#typing.ForwardRef" title="typing.ForwardRef"><code class="xref py py-class docutils literal notranslate">ForwardRef</code></a> objects are handled by evaluating them in globalns, localns, and (where applicable) obj’s <a class="reference internal" href="../reference/compound_stmts.html#type-params">type parameter</a> namespace. If globalns or localns is not given, appropriate namespace dictionaries are inferred from obj.</li> <li><code class="docutils literal notranslate">None</code> is replaced with <a class="reference internal" href="types.html#types.NoneType" title="types.NoneType"><code class="xref py py-class docutils literal notranslate">types.NoneType</code></a>.</li> <li>If <a class="reference internal" href="#typing.no_type_check" title="typing.no_type_check"><code class="xref py py-func docutils literal notranslate">@no_type_check</code></a> has been applied to obj, an empty dictionary is returned.</li> <li>If obj is a class <code class="docutils literal notranslate">C</code>, the function returns a dictionary that merges annotations from <code class="docutils literal notranslate">C</code>’s base classes with those on <code class="docutils literal notranslate">C</code> directly. This is done by traversing <a class="reference internal" href="../reference/datamodel.html#type.__mro__" title="type.__mro__"><code class="xref py py-attr docutils literal notranslate">C.__mro__</code></a> and iteratively combining <code class="docutils literal notranslate">__annotations__</code> dictionaries. Annotations on classes appearing earlier in the <a class="reference internal" href="../glossary.html#term-method-resolution-order">method resolution order</a> always take precedence over annotations on classes appearing later in the method resolution order.</li> <li>The function recursively replaces all occurrences of <code class="docutils literal notranslate">Annotated[T, ...]</code> with <code class="docutils literal notranslate">T</code>, unless include_extras is set to <code class="docutils literal notranslate">True</code> (see <a class="reference internal" href="#typing.Annotated" title="typing.Annotated"><code class="xref py py-class docutils literal notranslate">Annotated</code></a> for more information).</li> </ul> See also <a class="reference internal" href="inspect.html#inspect.get_annotations" title="inspect.get_annotations"><code class="xref py py-func docutils literal notranslate">inspect.get_annotations()</code></a>, a lower-level function that returns annotations more directly. <div class="admonition note"> Note If any forward references in the annotations of obj are not resolvable or are not valid Python code, this function will raise an exception such as <a class="reference internal" href="exceptions.html#NameError" title="NameError"><code class="xref py py-exc docutils literal notranslate">NameError</code></a>. For example, this can happen with imported <a class="reference internal" href="#type-aliases">type aliases</a> that include forward references, or with names imported under <a class="reference internal" href="#typing.TYPE_CHECKING" title="typing.TYPE_CHECKING"><code class="xref py py-data docutils literal notranslate">if TYPE_CHECKING</code></a>. </div> <div class="versionchanged"> Changed in version 3.9: Added <code class="docutils literal notranslate">include_extras</code> parameter as part of <a class="pep reference external" href="https://peps.python.org/pep-0593/">PEP 593</a>. See the documentation on <a class="reference internal" href="#typing.Annotated" title="typing.Annotated"><code class="xref py py-data docutils literal notranslate">Annotated</code></a> for more information. </div> <div class="versionchanged"> Changed in version 3.11: Previously, <code class="docutils literal notranslate">Optional[t]</code> was added for function and method annotations if a default value equal to <code class="docutils literal notranslate">None</code> was set. Now the annotation is returned unchanged. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.get_origin"> typing.get_origin(tp)<a class="headerlink" href="#typing.get_origin" title="Link to this definition">¶</a></dt> <dd>Get the unsubscripted version of a type: for a typing object of the form <code class="docutils literal notranslate">X[Y, Z, ...]</code> return <code class="docutils literal notranslate">X</code>. If <code class="docutils literal notranslate">X</code> is a typing-module alias for a builtin or <a class="reference internal" href="collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate">collections</code></a> class, it will be normalized to the original class. If <code class="docutils literal notranslate">X</code> is an instance of <a class="reference internal" href="#typing.ParamSpecArgs" title="typing.ParamSpecArgs"><code class="xref py py-class docutils literal notranslate">ParamSpecArgs</code></a> or <a class="reference internal" href="#typing.ParamSpecKwargs" title="typing.ParamSpecKwargs"><code class="xref py py-class docutils literal notranslate">ParamSpecKwargs</code></a>, return the underlying <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a>. Return <code class="docutils literal notranslate">None</code> for unsupported objects. Examples: <div class="highlight-python notranslate"><div class="highlight"><pre>assert get_origin(str) is None assert get_origin(Dict[str, int]) is dict assert get_origin(Union[int, str]) is Union assert get_origin(Annotated[str, "metadata"]) is Annotated P = ParamSpec('P') assert get_origin(P.args) is P assert get_origin(P.kwargs) is P </pre></div> </div> <div class="versionadded"> Added in version 3.8. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.get_args"> typing.get_args(tp)<a class="headerlink" href="#typing.get_args" title="Link to this definition">¶</a></dt> <dd>Get type arguments with all substitutions performed: for a typing object of the form <code class="docutils literal notranslate">X[Y, Z, ...]</code> return <code class="docutils literal notranslate">(Y, Z, ...)</code>. If <code class="docutils literal notranslate">X</code> is a union or <a class="reference internal" href="#typing.Literal" title="typing.Literal"><code class="xref py py-class docutils literal notranslate">Literal</code></a> contained in another generic type, the order of <code class="docutils literal notranslate">(Y, Z, ...)</code> may be different from the order of the original arguments <code class="docutils literal notranslate">[Y, Z, ...]</code> due to type caching. Return <code class="docutils literal notranslate">()</code> for unsupported objects. Examples: <div class="highlight-python notranslate"><div class="highlight"><pre>assert get_args(int) == () assert get_args(Dict[int, str]) == (int, str) assert get_args(Union[int, str]) == (int, str) </pre></div> </div> <div class="versionadded"> Added in version 3.8. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.get_protocol_members"> typing.get_protocol_members(tp)<a class="headerlink" href="#typing.get_protocol_members" title="Link to this definition">¶</a></dt> <dd>Return the set of members defined in a <a class="reference internal" href="#typing.Protocol" title="typing.Protocol"><code class="xref py py-class docutils literal notranslate">Protocol</code></a>. <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> from typing import Protocol, get_protocol_members >>> class P(Protocol): ... def a(self) -> str: ... ... b: int >>> get_protocol_members(P) == frozenset({'a', 'b'}) True </pre></div> </div> Raise <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> for arguments that are not Protocols. <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.is_protocol"> typing.is_protocol(tp)<a class="headerlink" href="#typing.is_protocol" title="Link to this definition">¶</a></dt> <dd>Determine if a type is a <a class="reference internal" href="#typing.Protocol" title="typing.Protocol"><code class="xref py py-class docutils literal notranslate">Protocol</code></a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class P(Protocol): def a(self) -> str: ... b: int is_protocol(P) # => True is_protocol(int) # => False </pre></div> </div> <div class="versionadded"> Added in version 3.13. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="typing.is_typeddict"> typing.is_typeddict(tp)<a class="headerlink" href="#typing.is_typeddict" title="Link to this definition">¶</a></dt> <dd>Check if a type is a <a class="reference internal" href="#typing.TypedDict" title="typing.TypedDict"><code class="xref py py-class docutils literal notranslate">TypedDict</code></a>. For example: <div class="highlight-python notranslate"><div class="highlight"><pre>class Film(TypedDict): title: str year: int assert is_typeddict(Film) assert not is_typeddict(list | str) # TypedDict is a factory for creating typed dicts, # not a typed dict itself assert not is_typeddict(TypedDict) </pre></div> </div> <div class="versionadded"> Added in version 3.10. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.ForwardRef"> class typing.ForwardRef<a class="headerlink" href="#typing.ForwardRef" title="Link to this definition">¶</a></dt> <dd>Class used for internal typing representation of string forward references. For example, <code class="docutils literal notranslate">List["SomeClass"]</code> is implicitly transformed into <code class="docutils literal notranslate">List[ForwardRef("SomeClass")]</code>. <code class="docutils literal notranslate">ForwardRef</code> should not be instantiated by a user, but may be used by introspection tools. <div class="admonition note"> Note <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> generic types such as <code class="docutils literal notranslate">list["SomeClass"]</code> will not be implicitly transformed into <code class="docutils literal notranslate">list[ForwardRef("SomeClass")]</code> and thus will not automatically resolve to <code class="docutils literal notranslate">list[SomeClass]</code>. </div> <div class="versionadded"> Added in version 3.7.4. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.NoDefault"> typing.NoDefault<a class="headerlink" href="#typing.NoDefault" title="Link to this definition">¶</a></dt> <dd>A sentinel object used to indicate that a type parameter has no default value. For example: <div class="highlight-pycon notranslate"><div class="highlight"><pre>>>> T = TypeVar("T") >>> T.__default__ is typing.NoDefault True >>> S = TypeVar("S", default=None) >>> S.__default__ is None True </pre></div> </div> <div class="versionadded"> Added in version 3.13. </div> </dd></dl> </section> <section id="constant"> <h3>Constant<a class="headerlink" href="#constant" title="Link to this heading">¶</a></h3> <dl class="py data"> <dt class="sig sig-object py" id="typing.TYPE_CHECKING"> typing.TYPE_CHECKING<a class="headerlink" href="#typing.TYPE_CHECKING" title="Link to this definition">¶</a></dt> <dd>A special constant that is assumed to be <code class="docutils literal notranslate">True</code> by 3rd party static type checkers. It is <code class="docutils literal notranslate">False</code> at runtime. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>if TYPE_CHECKING: import expensive_mod def fun(arg: 'expensive_mod.SomeType') -> None: local_var: expensive_mod.AnotherType = other_fun() </pre></div> </div> The first type annotation must be enclosed in quotes, making it a “forward reference”, to hide the <code class="docutils literal notranslate">expensive_mod</code> reference from the interpreter runtime. Type annotations for local variables are not evaluated, so the second annotation does not need to be enclosed in quotes. <div class="admonition note"> Note If <code class="docutils literal notranslate">from __future__ import annotations</code> is used, annotations are not evaluated at function definition time. Instead, they are stored as strings in <code class="docutils literal notranslate">__annotations__</code>. This makes it unnecessary to use quotes around the annotation (see <a class="pep reference external" href="https://peps.python.org/pep-0563/">PEP 563</a>). </div> <div class="versionadded"> Added in version 3.5.2. </div> </dd></dl> </section> <section id="deprecated-aliases"> <h3>Deprecated aliases<a class="headerlink" href="#deprecated-aliases" title="Link to this heading">¶</a></h3> This module defines several deprecated aliases to pre-existing standard library classes. These were originally included in the typing module in order to support parameterizing these generic classes using <code class="docutils literal notranslate">[]</code>. However, the aliases became redundant in Python 3.9 when the corresponding pre-existing classes were enhanced to support <code class="docutils literal notranslate">[]</code> (see <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a>). The redundant types are deprecated as of Python 3.9. However, while the aliases may be removed at some point, removal of these aliases is not currently planned. As such, no deprecation warnings are currently issued by the interpreter for these aliases. If at some point it is decided to remove these deprecated aliases, a deprecation warning will be issued by the interpreter for at least two releases prior to removal. The aliases are guaranteed to remain in the typing module without deprecation warnings until at least Python 3.14. Type checkers are encouraged to flag uses of the deprecated types if the program they are checking targets a minimum Python version of 3.9 or newer. <section id="aliases-to-built-in-types"> <h4>Aliases to built-in types<a class="headerlink" href="#aliases-to-built-in-types" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.Dict"> class typing.Dict(dict, MutableMapping[KT, VT])<a class="headerlink" href="#typing.Dict" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>. Note that to annotate arguments, it is preferred to use an abstract collection type such as <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate">Mapping</code></a> rather than to use <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a> or <code class="xref py py-class docutils literal notranslate">typing.Dict</code>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">builtins.dict</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.List"> class typing.List(list, MutableSequence[T])<a class="headerlink" href="#typing.List" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a>. Note that to annotate arguments, it is preferred to use an abstract collection type such as <a class="reference internal" href="collections.abc.html#collections.abc.Sequence" title="collections.abc.Sequence"><code class="xref py py-class docutils literal notranslate">Sequence</code></a> or <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal notranslate">Iterable</code></a> rather than to use <a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a> or <code class="xref py py-class docutils literal notranslate">typing.List</code>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">builtins.list</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Set"> class typing.Set(set, MutableSet[T])<a class="headerlink" href="#typing.Set" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">builtins.set</code></a>. Note that to annotate arguments, it is preferred to use an abstract collection type such as <a class="reference internal" href="collections.abc.html#collections.abc.Set" title="collections.abc.Set"><code class="xref py py-class docutils literal notranslate">collections.abc.Set</code></a> rather than to use <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">set</code></a> or <a class="reference internal" href="#typing.Set" title="typing.Set"><code class="xref py py-class docutils literal notranslate">typing.Set</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate">builtins.set</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.FrozenSet"> class typing.FrozenSet(frozenset, AbstractSet[T_co])<a class="headerlink" href="#typing.FrozenSet" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">builtins.frozenset</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate">builtins.frozenset</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Tuple"> typing.Tuple<a class="headerlink" href="#typing.Tuple" title="Link to this definition">¶</a></dt> <dd>Deprecated alias for <a class="reference internal" href="stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>. <a class="reference internal" href="stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> and <code class="docutils literal notranslate">Tuple</code> are special-cased in the type system; see <a class="reference internal" href="#annotating-tuples">Annotating tuples</a> for more details. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">builtins.tuple</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Type"> class typing.Type(Generic[CT_co])<a class="headerlink" href="#typing.Type" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a>. See <a class="reference internal" href="#type-of-class-objects">The type of class objects</a> for details on using <a class="reference internal" href="functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">type</code></a> or <code class="docutils literal notranslate">typing.Type</code> in type annotations. <div class="versionadded"> Added in version 3.5.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="functions.html#type" title="type"><code class="xref py py-class docutils literal notranslate">builtins.type</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> </section> <section id="aliases-to-types-in-collections"> <h4>Aliases to types in <a class="reference internal" href="collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate">collections</code></a><a class="headerlink" href="#aliases-to-types-in-collections" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.DefaultDict"> class typing.DefaultDict(collections.defaultdict, MutableMapping[KT, VT])<a class="headerlink" href="#typing.DefaultDict" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.html#collections.defaultdict" title="collections.defaultdict"><code class="xref py py-class docutils literal notranslate">collections.defaultdict</code></a>. <div class="versionadded"> Added in version 3.5.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.html#collections.defaultdict" title="collections.defaultdict"><code class="xref py py-class docutils literal notranslate">collections.defaultdict</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.OrderedDict"> class typing.OrderedDict(collections.OrderedDict, MutableMapping[KT, VT])<a class="headerlink" href="#typing.OrderedDict" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-class docutils literal notranslate">collections.OrderedDict</code></a>. <div class="versionadded"> Added in version 3.7.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-class docutils literal notranslate">collections.OrderedDict</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.ChainMap"> class typing.ChainMap(collections.ChainMap, MutableMapping[KT, VT])<a class="headerlink" href="#typing.ChainMap" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.html#collections.ChainMap" title="collections.ChainMap"><code class="xref py py-class docutils literal notranslate">collections.ChainMap</code></a>. <div class="versionadded"> Added in version 3.6.1. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.html#collections.ChainMap" title="collections.ChainMap"><code class="xref py py-class docutils literal notranslate">collections.ChainMap</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Counter"> class typing.Counter(collections.Counter, Dict[T, int])<a class="headerlink" href="#typing.Counter" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.html#collections.Counter" title="collections.Counter"><code class="xref py py-class docutils literal notranslate">collections.Counter</code></a>. <div class="versionadded"> Added in version 3.6.1. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.html#collections.Counter" title="collections.Counter"><code class="xref py py-class docutils literal notranslate">collections.Counter</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Deque"> class typing.Deque(deque, MutableSequence[T])<a class="headerlink" href="#typing.Deque" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.html#collections.deque" title="collections.deque"><code class="xref py py-class docutils literal notranslate">collections.deque</code></a>. <div class="versionadded"> Added in version 3.6.1. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.html#collections.deque" title="collections.deque"><code class="xref py py-class docutils literal notranslate">collections.deque</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> </section> <section id="aliases-to-other-concrete-types"> <h4>Aliases to other concrete types<a class="headerlink" href="#aliases-to-other-concrete-types" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.Pattern"> class typing.Pattern<a class="headerlink" href="#typing.Pattern" title="Link to this definition">¶</a></dt> <dt class="sig sig-object py" id="typing.Match"> class typing.Match<a class="headerlink" href="#typing.Match" title="Link to this definition">¶</a></dt> <dd>Deprecated aliases corresponding to the return types from <a class="reference internal" href="re.html#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate">re.compile()</code></a> and <a class="reference internal" href="re.html#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate">re.match()</code></a>. These types (and the corresponding functions) are generic over <a class="reference internal" href="#typing.AnyStr" title="typing.AnyStr"><code class="xref py py-data docutils literal notranslate">AnyStr</code></a>. <code class="docutils literal notranslate">Pattern</code> can be specialised as <code class="docutils literal notranslate">Pattern[str]</code> or <code class="docutils literal notranslate">Pattern[bytes]</code>; <code class="docutils literal notranslate">Match</code> can be specialised as <code class="docutils literal notranslate">Match[str]</code> or <code class="docutils literal notranslate">Match[bytes]</code>. <div class="deprecated"> Deprecated since version 3.9: Classes <code class="docutils literal notranslate">Pattern</code> and <code class="docutils literal notranslate">Match</code> from <a class="reference internal" href="re.html#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate">re</code></a> now support <code class="docutils literal notranslate">[]</code>. See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Text"> class typing.Text<a class="headerlink" href="#typing.Text" title="Link to this definition">¶</a></dt> <dd>Deprecated alias for <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>. <code class="docutils literal notranslate">Text</code> is provided to supply a forward compatible path for Python 2 code: in Python 2, <code class="docutils literal notranslate">Text</code> is an alias for <code class="docutils literal notranslate">unicode</code>. Use <code class="docutils literal notranslate">Text</code> to indicate that a value must contain a unicode string in a manner that is compatible with both Python 2 and Python 3: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def add_unicode_checkmark(text: Text) -> Text: return text + u' \u2713' </pre></div> </div> <div class="versionadded"> Added in version 3.5.2. </div> <div class="deprecated"> Deprecated since version 3.11: Python 2 is no longer supported, and most type checkers also no longer support type checking Python 2 code. Removal of the alias is not currently planned, but users are encouraged to use <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> instead of <code class="docutils literal notranslate">Text</code>. </div> </dd></dl> </section> <section id="aliases-to-container-abcs-in-collections-abc"> <h4>Aliases to container ABCs in <a class="reference internal" href="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><a class="headerlink" href="#aliases-to-container-abcs-in-collections-abc" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.AbstractSet"> class typing.AbstractSet(Collection[T_co])<a class="headerlink" href="#typing.AbstractSet" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Set" title="collections.abc.Set"><code class="xref py py-class docutils literal notranslate">collections.abc.Set</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Set" title="collections.abc.Set"><code class="xref py py-class docutils literal notranslate">collections.abc.Set</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.ByteString"> class typing.ByteString(Sequence[int])<a class="headerlink" href="#typing.ByteString" title="Link to this definition">¶</a></dt> <dd>This type represents the types <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>, <a class="reference internal" href="stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate">bytearray</code></a>, and <a class="reference internal" href="stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> of byte sequences. <div class="deprecated-removed"> Deprecated since version 3.9, will be removed in version 3.14: Prefer <a class="reference internal" href="collections.abc.html#collections.abc.Buffer" title="collections.abc.Buffer"><code class="xref py py-class docutils literal notranslate">collections.abc.Buffer</code></a>, or a union like <code class="docutils literal notranslate">bytes | bytearray | memoryview</code>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Collection"> class typing.Collection(Sized, Iterable[T_co], Container[T_co])<a class="headerlink" href="#typing.Collection" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Collection" title="collections.abc.Collection"><code class="xref py py-class docutils literal notranslate">collections.abc.Collection</code></a>. <div class="versionadded"> Added in version 3.6. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Collection" title="collections.abc.Collection"><code class="xref py py-class docutils literal notranslate">collections.abc.Collection</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Container"> class typing.Container(Generic[T_co])<a class="headerlink" href="#typing.Container" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Container" title="collections.abc.Container"><code class="xref py py-class docutils literal notranslate">collections.abc.Container</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Container" title="collections.abc.Container"><code class="xref py py-class docutils literal notranslate">collections.abc.Container</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.ItemsView"> class typing.ItemsView(MappingView, AbstractSet[tuple[KT_co, VT_co]])<a class="headerlink" href="#typing.ItemsView" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.ItemsView" title="collections.abc.ItemsView"><code class="xref py py-class docutils literal notranslate">collections.abc.ItemsView</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.ItemsView" title="collections.abc.ItemsView"><code class="xref py py-class docutils literal notranslate">collections.abc.ItemsView</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.KeysView"> class typing.KeysView(MappingView, AbstractSet[KT_co])<a class="headerlink" href="#typing.KeysView" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.KeysView" title="collections.abc.KeysView"><code class="xref py py-class docutils literal notranslate">collections.abc.KeysView</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.KeysView" title="collections.abc.KeysView"><code class="xref py py-class docutils literal notranslate">collections.abc.KeysView</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Mapping"> class typing.Mapping(Collection[KT], Generic[KT, VT_co])<a class="headerlink" href="#typing.Mapping" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate">collections.abc.Mapping</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate">collections.abc.Mapping</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.MappingView"> class typing.MappingView(Sized)<a class="headerlink" href="#typing.MappingView" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.MappingView" title="collections.abc.MappingView"><code class="xref py py-class docutils literal notranslate">collections.abc.MappingView</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.MappingView" title="collections.abc.MappingView"><code class="xref py py-class docutils literal notranslate">collections.abc.MappingView</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.MutableMapping"> class typing.MutableMapping(Mapping[KT, VT])<a class="headerlink" href="#typing.MutableMapping" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.MutableMapping" title="collections.abc.MutableMapping"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableMapping</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.MutableMapping" title="collections.abc.MutableMapping"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableMapping</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.MutableSequence"> class typing.MutableSequence(Sequence[T])<a class="headerlink" href="#typing.MutableSequence" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.MutableSequence" title="collections.abc.MutableSequence"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableSequence</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.MutableSequence" title="collections.abc.MutableSequence"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableSequence</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.MutableSet"> class typing.MutableSet(AbstractSet[T])<a class="headerlink" href="#typing.MutableSet" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.MutableSet" title="collections.abc.MutableSet"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableSet</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.MutableSet" title="collections.abc.MutableSet"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableSet</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Sequence"> class typing.Sequence(Reversible[T_co], Collection[T_co])<a class="headerlink" href="#typing.Sequence" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Sequence" title="collections.abc.Sequence"><code class="xref py py-class docutils literal notranslate">collections.abc.Sequence</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Sequence" title="collections.abc.Sequence"><code class="xref py py-class docutils literal notranslate">collections.abc.Sequence</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.ValuesView"> class typing.ValuesView(MappingView, Collection[_VT_co])<a class="headerlink" href="#typing.ValuesView" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.ValuesView" title="collections.abc.ValuesView"><code class="xref py py-class docutils literal notranslate">collections.abc.ValuesView</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.ValuesView" title="collections.abc.ValuesView"><code class="xref py py-class docutils literal notranslate">collections.abc.ValuesView</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> </section> <section id="aliases-to-asynchronous-abcs-in-collections-abc"> <h4>Aliases to asynchronous ABCs in <a class="reference internal" href="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><a class="headerlink" href="#aliases-to-asynchronous-abcs-in-collections-abc" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.Coroutine"> class typing.Coroutine(Awaitable[ReturnType], Generic[YieldType, SendType, ReturnType])<a class="headerlink" href="#typing.Coroutine" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Coroutine" title="collections.abc.Coroutine"><code class="xref py py-class docutils literal notranslate">collections.abc.Coroutine</code></a>. See <a class="reference internal" href="#annotating-generators-and-coroutines">Annotating generators and coroutines</a> for details on using <a class="reference internal" href="collections.abc.html#collections.abc.Coroutine" title="collections.abc.Coroutine"><code class="xref py py-class docutils literal notranslate">collections.abc.Coroutine</code></a> and <code class="docutils literal notranslate">typing.Coroutine</code> in type annotations. <div class="versionadded"> Added in version 3.5.3. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Coroutine" title="collections.abc.Coroutine"><code class="xref py py-class docutils literal notranslate">collections.abc.Coroutine</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.AsyncGenerator"> class typing.AsyncGenerator(AsyncIterator[YieldType], Generic[YieldType, SendType])<a class="headerlink" href="#typing.AsyncGenerator" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.AsyncGenerator" title="collections.abc.AsyncGenerator"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncGenerator</code></a>. See <a class="reference internal" href="#annotating-generators-and-coroutines">Annotating generators and coroutines</a> for details on using <a class="reference internal" href="collections.abc.html#collections.abc.AsyncGenerator" title="collections.abc.AsyncGenerator"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncGenerator</code></a> and <code class="docutils literal notranslate">typing.AsyncGenerator</code> in type annotations. <div class="versionadded"> Added in version 3.6.1. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.AsyncGenerator" title="collections.abc.AsyncGenerator"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncGenerator</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> <div class="versionchanged"> Changed in version 3.13: The <code class="docutils literal notranslate">SendType</code> parameter now has a default. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.AsyncIterable"> class typing.AsyncIterable(Generic[T_co])<a class="headerlink" href="#typing.AsyncIterable" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.AsyncIterable" title="collections.abc.AsyncIterable"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncIterable</code></a>. <div class="versionadded"> Added in version 3.5.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.AsyncIterable" title="collections.abc.AsyncIterable"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncIterable</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.AsyncIterator"> class typing.AsyncIterator(AsyncIterable[T_co])<a class="headerlink" href="#typing.AsyncIterator" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.AsyncIterator" title="collections.abc.AsyncIterator"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncIterator</code></a>. <div class="versionadded"> Added in version 3.5.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.AsyncIterator" title="collections.abc.AsyncIterator"><code class="xref py py-class docutils literal notranslate">collections.abc.AsyncIterator</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Awaitable"> class typing.Awaitable(Generic[T_co])<a class="headerlink" href="#typing.Awaitable" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Awaitable" title="collections.abc.Awaitable"><code class="xref py py-class docutils literal notranslate">collections.abc.Awaitable</code></a>. <div class="versionadded"> Added in version 3.5.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Awaitable" title="collections.abc.Awaitable"><code class="xref py py-class docutils literal notranslate">collections.abc.Awaitable</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> </section> <section id="aliases-to-other-abcs-in-collections-abc"> <h4>Aliases to other ABCs in <a class="reference internal" href="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><a class="headerlink" href="#aliases-to-other-abcs-in-collections-abc" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.Iterable"> class typing.Iterable(Generic[T_co])<a class="headerlink" href="#typing.Iterable" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal notranslate">collections.abc.Iterable</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Iterable" title="collections.abc.Iterable"><code class="xref py py-class docutils literal notranslate">collections.abc.Iterable</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Iterator"> class typing.Iterator(Iterable[T_co])<a class="headerlink" href="#typing.Iterator" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Iterator" title="collections.abc.Iterator"><code class="xref py py-class docutils literal notranslate">collections.abc.Iterator</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Iterator" title="collections.abc.Iterator"><code class="xref py py-class docutils literal notranslate">collections.abc.Iterator</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py data"> <dt class="sig sig-object py" id="typing.Callable"> typing.Callable<a class="headerlink" href="#typing.Callable" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Callable" title="collections.abc.Callable"><code class="xref py py-class docutils literal notranslate">collections.abc.Callable</code></a>. See <a class="reference internal" href="#annotating-callables">Annotating callable objects</a> for details on how to use <a class="reference internal" href="collections.abc.html#collections.abc.Callable" title="collections.abc.Callable"><code class="xref py py-class docutils literal notranslate">collections.abc.Callable</code></a> and <code class="docutils literal notranslate">typing.Callable</code> in type annotations. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Callable" title="collections.abc.Callable"><code class="xref py py-class docutils literal notranslate">collections.abc.Callable</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> <div class="versionchanged"> Changed in version 3.10: <code class="docutils literal notranslate">Callable</code> now supports <a class="reference internal" href="#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">ParamSpec</code></a> and <a class="reference internal" href="#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-data docutils literal notranslate">Concatenate</code></a>. See <a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a> for more details. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Generator"> class typing.Generator(Iterator[YieldType], Generic[YieldType, SendType, ReturnType])<a class="headerlink" href="#typing.Generator" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Generator" title="collections.abc.Generator"><code class="xref py py-class docutils literal notranslate">collections.abc.Generator</code></a>. See <a class="reference internal" href="#annotating-generators-and-coroutines">Annotating generators and coroutines</a> for details on using <a class="reference internal" href="collections.abc.html#collections.abc.Generator" title="collections.abc.Generator"><code class="xref py py-class docutils literal notranslate">collections.abc.Generator</code></a> and <code class="docutils literal notranslate">typing.Generator</code> in type annotations. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Generator" title="collections.abc.Generator"><code class="xref py py-class docutils literal notranslate">collections.abc.Generator</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> <div class="versionchanged"> Changed in version 3.13: Default values for the send and return types were added. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Hashable"> class typing.Hashable<a class="headerlink" href="#typing.Hashable" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Hashable" title="collections.abc.Hashable"><code class="xref py py-class docutils literal notranslate">collections.abc.Hashable</code></a>. <div class="deprecated"> Deprecated since version 3.12: Use <a class="reference internal" href="collections.abc.html#collections.abc.Hashable" title="collections.abc.Hashable"><code class="xref py py-class docutils literal notranslate">collections.abc.Hashable</code></a> directly instead. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Reversible"> class typing.Reversible(Iterable[T_co])<a class="headerlink" href="#typing.Reversible" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Reversible" title="collections.abc.Reversible"><code class="xref py py-class docutils literal notranslate">collections.abc.Reversible</code></a>. <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="collections.abc.html#collections.abc.Reversible" title="collections.abc.Reversible"><code class="xref py py-class docutils literal notranslate">collections.abc.Reversible</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.Sized"> class typing.Sized<a class="headerlink" href="#typing.Sized" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="collections.abc.html#collections.abc.Sized" title="collections.abc.Sized"><code class="xref py py-class docutils literal notranslate">collections.abc.Sized</code></a>. <div class="deprecated"> Deprecated since version 3.12: Use <a class="reference internal" href="collections.abc.html#collections.abc.Sized" title="collections.abc.Sized"><code class="xref py py-class docutils literal notranslate">collections.abc.Sized</code></a> directly instead. </div> </dd></dl> </section> <section id="aliases-to-contextlib-abcs"> <h4>Aliases to <a class="reference internal" href="contextlib.html#module-contextlib" title="contextlib: Utilities for with-statement contexts."><code class="xref py py-mod docutils literal notranslate">contextlib</code></a> ABCs<a class="headerlink" href="#aliases-to-contextlib-abcs" title="Link to this heading">¶</a></h4> <dl class="py class"> <dt class="sig sig-object py" id="typing.ContextManager"> class typing.ContextManager(Generic[T_co, ExitT_co])<a class="headerlink" href="#typing.ContextManager" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="contextlib.html#contextlib.AbstractContextManager" title="contextlib.AbstractContextManager"><code class="xref py py-class docutils literal notranslate">contextlib.AbstractContextManager</code></a>. The first type parameter, <code class="docutils literal notranslate">T_co</code>, represents the type returned by the <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate">__enter__()</code></a> method. The optional second type parameter, <code class="docutils literal notranslate">ExitT_co</code>, which defaults to <code class="docutils literal notranslate">bool | None</code>, represents the type returned by the <a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate">__exit__()</code></a> method. <div class="versionadded"> Added in version 3.5.4. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="contextlib.html#contextlib.AbstractContextManager" title="contextlib.AbstractContextManager"><code class="xref py py-class docutils literal notranslate">contextlib.AbstractContextManager</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> <div class="versionchanged"> Changed in version 3.13: Added the optional second type parameter, <code class="docutils literal notranslate">ExitT_co</code>. </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="typing.AsyncContextManager"> class typing.AsyncContextManager(Generic[T_co, AExitT_co])<a class="headerlink" href="#typing.AsyncContextManager" title="Link to this definition">¶</a></dt> <dd>Deprecated alias to <a class="reference internal" href="contextlib.html#contextlib.AbstractAsyncContextManager" title="contextlib.AbstractAsyncContextManager"><code class="xref py py-class docutils literal notranslate">contextlib.AbstractAsyncContextManager</code></a>. The first type parameter, <code class="docutils literal notranslate">T_co</code>, represents the type returned by the <a class="reference internal" href="../reference/datamodel.html#object.__aenter__" title="object.__aenter__"><code class="xref py py-meth docutils literal notranslate">__aenter__()</code></a> method. The optional second type parameter, <code class="docutils literal notranslate">AExitT_co</code>, which defaults to <code class="docutils literal notranslate">bool | None</code>, represents the type returned by the <a class="reference internal" href="../reference/datamodel.html#object.__aexit__" title="object.__aexit__"><code class="xref py py-meth docutils literal notranslate">__aexit__()</code></a> method. <div class="versionadded"> Added in version 3.6.2. </div> <div class="deprecated"> Deprecated since version 3.9: <a class="reference internal" href="contextlib.html#contextlib.AbstractAsyncContextManager" title="contextlib.AbstractAsyncContextManager"><code class="xref py py-class docutils literal notranslate">contextlib.AbstractAsyncContextManager</code></a> now supports subscripting (<code class="docutils literal notranslate">[]</code>). See <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a> and <a class="reference internal" href="stdtypes.html#types-genericalias">Generic Alias Type</a>. </div> <div class="versionchanged"> Changed in version 3.13: Added the optional second type parameter, <code class="docutils literal notranslate">AExitT_co</code>. </div> </dd></dl> </section> </section> </section> <section id="deprecation-timeline-of-major-features"> <h2>Deprecation Timeline of Major Features<a class="headerlink" href="#deprecation-timeline-of-major-features" title="Link to this heading">¶</a></h2> Certain features in <code class="docutils literal notranslate">typing</code> are deprecated and may be removed in a future version of Python. The following table summarizes major deprecations for your convenience. This is subject to change, and not all deprecations are listed. <table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Feature</th> <th class="head">Deprecated in</th> <th class="head">Projected removal</th> <th class="head">PEP/issue</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">typing</code> versions of standard collections</td> <td>3.9</td> <td>Undecided (see <a class="reference internal" href="#deprecated-aliases">Deprecated aliases</a> for more information)</td> <td><a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a></td> </tr> <tr class="row-odd"><td><a class="reference internal" href="#typing.ByteString" title="typing.ByteString"><code class="xref py py-class docutils literal notranslate">typing.ByteString</code></a></td> <td>3.9</td> <td>3.14</td> <td><a class="reference external" href="https://github.com/python/cpython/issues/91896">gh-91896</a></td> </tr> <tr class="row-even"><td><a class="reference internal" href="#typing.Text" title="typing.Text"><code class="xref py py-data docutils literal notranslate">typing.Text</code></a></td> <td>3.11</td> <td>Undecided</td> <td><a class="reference external" href="https://github.com/python/cpython/issues/92332">gh-92332</a></td> </tr> <tr class="row-odd"><td><a class="reference internal" href="#typing.Hashable" title="typing.Hashable"><code class="xref py py-class docutils literal notranslate">typing.Hashable</code></a> and <a class="reference internal" href="#typing.Sized" title="typing.Sized"><code class="xref py py-class docutils literal notranslate">typing.Sized</code></a></td> <td>3.12</td> <td>Undecided</td> <td><a class="reference external" href="https://github.com/python/cpython/issues/94309">gh-94309</a></td> </tr> <tr class="row-even"><td><a class="reference internal" href="#typing.TypeAlias" title="typing.TypeAlias"><code class="xref py py-data docutils literal notranslate">typing.TypeAlias</code></a></td> <td>3.12</td> <td>Undecided</td> <td><a class="pep reference external" href="https://peps.python.org/pep-0695/">PEP 695</a></td> </tr> <tr class="row-odd"><td><a class="reference internal" href="#typing.no_type_check_decorator" title="typing.no_type_check_decorator"><code class="xref py py-func docutils literal notranslate">@typing.no_type_check_decorator</code></a></td> <td>3.13</td> <td>3.15</td> <td><a class="reference external" href="https://github.com/python/cpython/issues/106309">gh-106309</a></td> </tr> <tr class="row-even"><td><a class="reference internal" href="#typing.AnyStr" title="typing.AnyStr"><code class="xref py py-data docutils literal notranslate">typing.AnyStr</code></a></td> <td>3.13</td> <td>3.18</td> <td><a class="reference external" href="https://github.com/python/cpython/issues/105578">gh-105578</a></td> </tr> </tbody> </table> </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="#"><code class="xref py py-mod docutils literal notranslate">typing</code> — Support for type hints</a><ul> <li><a class="reference internal" href="#specification-for-the-python-type-system">Specification for the Python Type System</a></li> <li><a class="reference internal" href="#type-aliases">Type aliases</a></li> <li><a class="reference internal" href="#newtype">NewType</a></li> <li><a class="reference internal" href="#annotating-callable-objects">Annotating callable objects</a></li> <li><a class="reference internal" href="#generics">Generics</a></li> <li><a class="reference internal" href="#annotating-tuples">Annotating tuples</a></li> <li><a class="reference internal" href="#the-type-of-class-objects">The type of class objects</a></li> <li><a class="reference internal" href="#annotating-generators-and-coroutines">Annotating generators and coroutines</a></li> <li><a class="reference internal" href="#user-defined-generic-types">User-defined generic types</a></li> <li><a class="reference internal" href="#the-any-type">The <code class="xref py py-data docutils literal notranslate">Any</code> type</a></li> <li><a class="reference internal" href="#nominal-vs-structural-subtyping">Nominal vs structural subtyping</a></li> <li><a class="reference internal" href="#module-contents">Module contents</a><ul> <li><a class="reference internal" href="#special-typing-primitives">Special typing primitives</a><ul> <li><a class="reference internal" href="#special-types">Special types</a><ul> <li><a class="reference internal" href="#typing.Any"><code class="docutils literal notranslate">Any</code></a></li> <li><a class="reference internal" href="#typing.AnyStr"><code class="docutils literal notranslate">AnyStr</code></a></li> <li><a class="reference internal" href="#typing.LiteralString"><code class="docutils literal notranslate">LiteralString</code></a></li> <li><a class="reference internal" href="#typing.Never"><code class="docutils literal notranslate">Never</code></a></li> <li><a class="reference internal" href="#typing.NoReturn"><code class="docutils literal notranslate">NoReturn</code></a></li> <li><a class="reference internal" href="#typing.Self"><code class="docutils literal notranslate">Self</code></a></li> <li><a class="reference internal" href="#typing.TypeAlias"><code class="docutils literal notranslate">TypeAlias</code></a></li> </ul> </li> <li><a class="reference internal" href="#special-forms">Special forms</a><ul> <li><a class="reference internal" href="#typing.Union"><code class="docutils literal notranslate">Union</code></a></li> <li><a class="reference internal" href="#typing.Optional"><code class="docutils literal notranslate">Optional</code></a></li> <li><a class="reference internal" href="#typing.Concatenate"><code class="docutils literal notranslate">Concatenate</code></a></li> <li><a class="reference internal" href="#typing.Literal"><code class="docutils literal notranslate">Literal</code></a></li> <li><a class="reference internal" href="#typing.ClassVar"><code class="docutils literal notranslate">ClassVar</code></a></li> <li><a class="reference internal" href="#typing.Final"><code class="docutils literal notranslate">Final</code></a></li> <li><a class="reference internal" href="#typing.Required"><code class="docutils literal notranslate">Required</code></a></li> <li><a class="reference internal" href="#typing.NotRequired"><code class="docutils literal notranslate">NotRequired</code></a></li> <li><a class="reference internal" href="#typing.ReadOnly"><code class="docutils literal notranslate">ReadOnly</code></a></li> <li><a class="reference internal" href="#typing.Annotated"><code class="docutils literal notranslate">Annotated</code></a></li> <li><a class="reference internal" href="#typing.TypeIs"><code class="docutils literal notranslate">TypeIs</code></a></li> <li><a class="reference internal" href="#typing.TypeGuard"><code class="docutils literal notranslate">TypeGuard</code></a></li> <li><a class="reference internal" href="#typing.Unpack"><code class="docutils literal notranslate">Unpack</code></a></li> </ul> </li> <li><a class="reference internal" href="#building-generic-types-and-type-aliases">Building generic types and type aliases</a><ul> <li><a class="reference internal" href="#typing.Generic"><code class="docutils literal notranslate">Generic</code></a></li> <li><a class="reference internal" href="#typing.TypeVar"><code class="docutils literal notranslate">TypeVar</code></a><ul> <li><a class="reference internal" href="#typing.TypeVar.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__covariant__"><code class="docutils literal notranslate">__covariant__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__contravariant__"><code class="docutils literal notranslate">__contravariant__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__infer_variance__"><code class="docutils literal notranslate">__infer_variance__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__bound__"><code class="docutils literal notranslate">__bound__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__constraints__"><code class="docutils literal notranslate">__constraints__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.__default__"><code class="docutils literal notranslate">__default__</code></a></li> <li><a class="reference internal" href="#typing.TypeVar.has_default"><code class="docutils literal notranslate">has_default()</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.TypeVarTuple"><code class="docutils literal notranslate">TypeVarTuple</code></a><ul> <li><a class="reference internal" href="#typing.TypeVarTuple.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.TypeVarTuple.__default__"><code class="docutils literal notranslate">__default__</code></a></li> <li><a class="reference internal" href="#typing.TypeVarTuple.has_default"><code class="docutils literal notranslate">has_default()</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.ParamSpec"><code class="docutils literal notranslate">ParamSpec</code></a><ul> <li><a class="reference internal" href="#typing.ParamSpec.args"><code class="docutils literal notranslate">args</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.kwargs"><code class="docutils literal notranslate">kwargs</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.__default__"><code class="docutils literal notranslate">__default__</code></a></li> <li><a class="reference internal" href="#typing.ParamSpec.has_default"><code class="docutils literal notranslate">has_default()</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.ParamSpecArgs"><code class="docutils literal notranslate">ParamSpecArgs</code></a></li> <li><a class="reference internal" href="#typing.ParamSpecKwargs"><code class="docutils literal notranslate">ParamSpecKwargs</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType"><code class="docutils literal notranslate">TypeAliasType</code></a><ul> <li><a class="reference internal" href="#typing.TypeAliasType.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType.__type_params__"><code class="docutils literal notranslate">__type_params__</code></a></li> <li><a class="reference internal" href="#typing.TypeAliasType.__value__"><code class="docutils literal notranslate">__value__</code></a></li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#other-special-directives">Other special directives</a><ul> <li><a class="reference internal" href="#typing.NamedTuple"><code class="docutils literal notranslate">NamedTuple</code></a></li> <li><a class="reference internal" href="#typing.NewType"><code class="docutils literal notranslate">NewType</code></a><ul> <li><a class="reference internal" href="#typing.NewType.__module__"><code class="docutils literal notranslate">__module__</code></a></li> <li><a class="reference internal" href="#typing.NewType.__name__"><code class="docutils literal notranslate">__name__</code></a></li> <li><a class="reference internal" href="#typing.NewType.__supertype__"><code class="docutils literal notranslate">__supertype__</code></a></li> </ul> </li> <li><a class="reference internal" href="#typing.Protocol"><code class="docutils literal notranslate">Protocol</code></a></li> <li><a class="reference internal" href="#typing.runtime_checkable"><code class="docutils literal notranslate">runtime_checkable()</code></a></li> <li><a class="reference internal" href="#typing.TypedDict"><code class="docutils literal notranslate">TypedDict</code></a><ul> <li><a class="reference internal" href="#typing.TypedDict.__total__"><code class="docutils literal notranslate">__total__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__required_keys__"><code class="docutils literal notranslate">__required_keys__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__optional_keys__"><code class="docutils literal notranslate">__optional_keys__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__readonly_keys__"><code class="docutils literal notranslate">__readonly_keys__</code></a></li> <li><a class="reference internal" href="#typing.TypedDict.__mutable_keys__"><code class="docutils literal notranslate">__mutable_keys__</code></a></li> </ul> </li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#protocols">Protocols</a><ul> <li><a class="reference internal" href="#typing.SupportsAbs"><code class="docutils literal notranslate">SupportsAbs</code></a></li> <li><a class="reference internal" href="#typing.SupportsBytes"><code class="docutils literal notranslate">SupportsBytes</code></a></li> <li><a class="reference internal" href="#typing.SupportsComplex"><code class="docutils literal notranslate">SupportsComplex</code></a></li> <li><a class="reference internal" href="#typing.SupportsFloat"><code class="docutils literal notranslate">SupportsFloat</code></a></li> <li><a class="reference internal" href="#typing.SupportsIndex"><code class="docutils literal notranslate">SupportsIndex</code></a></li> <li><a class="reference internal" href="#typing.SupportsInt"><code class="docutils literal notranslate">SupportsInt</code></a></li> <li><a class="reference internal" href="#typing.SupportsRound"><code class="docutils literal notranslate">SupportsRound</code></a></li> </ul> </li> <li><a class="reference internal" href="#abcs-for-working-with-io">ABCs for working with IO</a><ul> <li><a class="reference internal" href="#typing.IO"><code class="docutils literal notranslate">IO</code></a></li> <li><a class="reference internal" href="#typing.TextIO"><code class="docutils literal notranslate">TextIO</code></a></li> <li><a class="reference internal" href="#typing.BinaryIO"><code class="docutils literal notranslate">BinaryIO</code></a></li> </ul> </li> <li><a class="reference internal" href="#functions-and-decorators">Functions and decorators</a><ul> <li><a class="reference internal" href="#typing.cast"><code class="docutils literal notranslate">cast()</code></a></li> <li><a class="reference internal" href="#typing.assert_type"><code class="docutils literal notranslate">assert_type()</code></a></li> <li><a class="reference internal" href="#typing.assert_never"><code class="docutils literal notranslate">assert_never()</code></a></li> <li><a class="reference internal" href="#typing.reveal_type"><code class="docutils literal notranslate">reveal_type()</code></a></li> <li><a class="reference internal" href="#typing.dataclass_transform"><code class="docutils literal notranslate">dataclass_transform()</code></a></li> <li><a class="reference internal" href="#typing.overload"><code class="docutils literal notranslate">overload()</code></a></li> <li><a class="reference internal" href="#typing.get_overloads"><code class="docutils literal notranslate">get_overloads()</code></a></li> <li><a class="reference internal" href="#typing.clear_overloads"><code class="docutils literal notranslate">clear_overloads()</code></a></li> <li><a class="reference internal" href="#typing.final"><code class="docutils literal notranslate">final()</code></a></li> <li><a class="reference internal" href="#typing.no_type_check"><code class="docutils literal notranslate">no_type_check()</code></a></li> <li><a class="reference internal" href="#typing.no_type_check_decorator"><code class="docutils literal notranslate">no_type_check_decorator()</code></a></li> <li><a class="reference internal" href="#typing.override"><code class="docutils literal notranslate">override()</code></a></li> <li><a class="reference internal" href="#typing.type_check_only"><code class="docutils literal notranslate">type_check_only()</code></a></li> </ul> </li> <li><a class="reference internal" href="#introspection-helpers">Introspection helpers</a><ul> <li><a class="reference internal" href="#typing.get_type_hints"><code class="docutils literal notranslate">get_type_hints()</code></a></li> <li><a class="reference internal" href="#typing.get_origin"><code class="docutils literal notranslate">get_origin()</code></a></li> <li><a class="reference internal" href="#typing.get_args"><code class="docutils literal notranslate">get_args()</code></a></li> <li><a class="reference internal" href="#typing.get_protocol_members"><code class="docutils literal notranslate">get_protocol_members()</code></a></li> <li><a class="reference internal" href="#typing.is_protocol"><code class="docutils literal notranslate">is_protocol()</code></a></li> <li><a class="reference internal" href="#typing.is_typeddict"><code class="docutils literal notranslate">is_typeddict()</code></a></li> <li><a class="reference internal" href="#typing.ForwardRef"><code class="docutils literal notranslate">ForwardRef</code></a></li> <li><a class="reference internal" href="#typing.NoDefault"><code class="docutils literal notranslate">NoDefault</code></a></li> </ul> </li> <li><a class="reference internal" href="#constant">Constant</a><ul> <li><a class="reference internal" href="#typing.TYPE_CHECKING"><code class="docutils literal notranslate">TYPE_CHECKING</code></a></li> </ul> </li> <li><a class="reference internal" href="#deprecated-aliases">Deprecated aliases</a><ul> <li><a class="reference internal" href="#aliases-to-built-in-types">Aliases to built-in types</a><ul> <li><a class="reference internal" href="#typing.Dict"><code class="docutils literal notranslate">Dict</code></a></li> <li><a class="reference internal" href="#typing.List"><code class="docutils literal notranslate">List</code></a></li> <li><a class="reference internal" href="#typing.Set"><code class="docutils literal notranslate">Set</code></a></li> <li><a class="reference internal" href="#typing.FrozenSet"><code class="docutils literal notranslate">FrozenSet</code></a></li> <li><a class="reference internal" href="#typing.Tuple"><code class="docutils literal notranslate">Tuple</code></a></li> <li><a class="reference internal" href="#typing.Type"><code class="docutils literal notranslate">Type</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-types-in-collections">Aliases to types in <code class="xref py py-mod docutils literal notranslate">collections</code></a><ul> <li><a class="reference internal" href="#typing.DefaultDict"><code class="docutils literal notranslate">DefaultDict</code></a></li> <li><a class="reference internal" href="#typing.OrderedDict"><code class="docutils literal notranslate">OrderedDict</code></a></li> <li><a class="reference internal" href="#typing.ChainMap"><code class="docutils literal notranslate">ChainMap</code></a></li> <li><a class="reference internal" href="#typing.Counter"><code class="docutils literal notranslate">Counter</code></a></li> <li><a class="reference internal" href="#typing.Deque"><code class="docutils literal notranslate">Deque</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-other-concrete-types">Aliases to other concrete types</a><ul> <li><a class="reference internal" href="#typing.Pattern"><code class="docutils literal notranslate">Pattern</code></a></li> <li><a class="reference internal" href="#typing.Match"><code class="docutils literal notranslate">Match</code></a></li> <li><a class="reference internal" href="#typing.Text"><code class="docutils literal notranslate">Text</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-container-abcs-in-collections-abc">Aliases to container ABCs in <code class="xref py py-mod docutils literal notranslate">collections.abc</code></a><ul> <li><a class="reference internal" href="#typing.AbstractSet"><code class="docutils literal notranslate">AbstractSet</code></a></li> <li><a class="reference internal" href="#typing.ByteString"><code class="docutils literal notranslate">ByteString</code></a></li> <li><a class="reference internal" href="#typing.Collection"><code class="docutils literal notranslate">Collection</code></a></li> <li><a class="reference internal" href="#typing.Container"><code class="docutils literal notranslate">Container</code></a></li> <li><a class="reference internal" href="#typing.ItemsView"><code class="docutils literal notranslate">ItemsView</code></a></li> <li><a class="reference internal" href="#typing.KeysView"><code class="docutils literal notranslate">KeysView</code></a></li> <li><a class="reference internal" href="#typing.Mapping"><code class="docutils literal notranslate">Mapping</code></a></li> <li><a class="reference internal" href="#typing.MappingView"><code class="docutils literal notranslate">MappingView</code></a></li> <li><a class="reference internal" href="#typing.MutableMapping"><code class="docutils literal notranslate">MutableMapping</code></a></li> <li><a class="reference internal" href="#typing.MutableSequence"><code class="docutils literal notranslate">MutableSequence</code></a></li> <li><a class="reference internal" href="#typing.MutableSet"><code class="docutils literal notranslate">MutableSet</code></a></li> <li><a class="reference internal" href="#typing.Sequence"><code class="docutils literal notranslate">Sequence</code></a></li> <li><a class="reference internal" href="#typing.ValuesView"><code class="docutils literal notranslate">ValuesView</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-asynchronous-abcs-in-collections-abc">Aliases to asynchronous ABCs in <code class="xref py py-mod docutils literal notranslate">collections.abc</code></a><ul> <li><a class="reference internal" href="#typing.Coroutine"><code class="docutils literal notranslate">Coroutine</code></a></li> <li><a class="reference internal" href="#typing.AsyncGenerator"><code class="docutils literal notranslate">AsyncGenerator</code></a></li> <li><a class="reference internal" href="#typing.AsyncIterable"><code class="docutils literal notranslate">AsyncIterable</code></a></li> <li><a class="reference internal" href="#typing.AsyncIterator"><code class="docutils literal notranslate">AsyncIterator</code></a></li> <li><a class="reference internal" href="#typing.Awaitable"><code class="docutils literal notranslate">Awaitable</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-other-abcs-in-collections-abc">Aliases to other ABCs in <code class="xref py py-mod docutils literal notranslate">collections.abc</code></a><ul> <li><a class="reference internal" href="#typing.Iterable"><code class="docutils literal notranslate">Iterable</code></a></li> <li><a class="reference internal" href="#typing.Iterator"><code class="docutils literal notranslate">Iterator</code></a></li> <li><a class="reference internal" href="#typing.Callable"><code class="docutils literal notranslate">Callable</code></a></li> <li><a class="reference internal" href="#typing.Generator"><code class="docutils literal notranslate">Generator</code></a></li> <li><a class="reference internal" href="#typing.Hashable"><code class="docutils literal notranslate">Hashable</code></a></li> <li><a class="reference internal" href="#typing.Reversible"><code class="docutils literal notranslate">Reversible</code></a></li> <li><a class="reference internal" href="#typing.Sized"><code class="docutils literal notranslate">Sized</code></a></li> </ul> </li> <li><a class="reference internal" href="#aliases-to-contextlib-abcs">Aliases to <code class="xref py py-mod docutils literal notranslate">contextlib</code> ABCs</a><ul> <li><a class="reference internal" href="#typing.ContextManager"><code class="docutils literal notranslate">ContextManager</code></a></li> <li><a class="reference internal" href="#typing.AsyncContextManager"><code class="docutils literal notranslate">AsyncContextManager</code></a></li> </ul> </li> </ul> </li> </ul> </li> <li><a class="reference internal" href="#deprecation-timeline-of-major-features">Deprecation Timeline of Major Features</a></li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="development.html" title="previous chapter">Development Tools</a> </div> <div> <h4>Next topic</h4> <a href="pydoc.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate">pydoc</code> — Documentation generator and online help system</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/library/typing.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> <div id="sidebarbutton" title="Collapse sidebar"> « </div> </div> <div class="clearer"></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" 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