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Often seen for code examples which can be executed interactively in the interpreter. </dd> <dt id="term-..."><code class="docutils literal notranslate">...</code><a class="headerlink" href="#term-..." title="Link to this term">¶</a></dt><dd>Can refer to: <ul class="simple"> <li>The default Python prompt of the <a class="reference internal" href="#term-interactive">interactive</a> shell when entering the code for an indented code block, when within a pair of matching left and right delimiters (parentheses, square brackets, curly braces or triple quotes), or after specifying a decorator.</li> <li>The <a class="reference internal" href="library/constants.html#Ellipsis" title="Ellipsis"><code class="xref py py-const docutils literal notranslate">Ellipsis</code></a> built-in constant.</li> </ul> </dd> <dt id="term-abstract-base-class">abstract base class<a class="headerlink" href="#term-abstract-base-class" title="Link to this term">¶</a></dt><dd>Abstract base classes complement <a class="reference internal" href="#term-duck-typing">duck-typing</a> by providing a way to define interfaces when other techniques like <a class="reference internal" href="library/functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate">hasattr()</code></a> would be clumsy or subtly wrong (for example with <a class="reference internal" href="reference/datamodel.html#special-lookup">magic methods</a>). ABCs introduce virtual subclasses, which are classes that don’t inherit from a class but are still recognized by <a class="reference internal" href="library/functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> and <a class="reference internal" href="library/functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate">issubclass()</code></a>; see the <a class="reference internal" href="library/abc.html#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate">abc</code></a> module documentation. Python comes with many built-in ABCs for data structures (in the <a class="reference internal" href="library/collections.abc.html#module-collections.abc" title="collections.abc: Abstract base classes for containers"><code class="xref py py-mod docutils literal notranslate">collections.abc</code></a> module), numbers (in the <a class="reference internal" href="library/numbers.html#module-numbers" title="numbers: Numeric abstract base classes (Complex, Real, Integral, etc.)."><code class="xref py py-mod docutils literal notranslate">numbers</code></a> module), streams (in the <a class="reference internal" href="library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate">io</code></a> module), import finders and loaders (in the <a class="reference internal" href="library/importlib.html#module-importlib.abc" title="importlib.abc: Abstract base classes related to import"><code class="xref py py-mod docutils literal notranslate">importlib.abc</code></a> module). You can create your own ABCs with the <a class="reference internal" href="library/abc.html#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate">abc</code></a> module. </dd> <dt id="term-annotation">annotation<a class="headerlink" href="#term-annotation" title="Link to this term">¶</a></dt><dd>A label associated with a variable, a class attribute or a function parameter or return value, used by convention as a <a class="reference internal" href="#term-type-hint">type hint</a>. Annotations of local variables cannot be accessed at runtime, but annotations of global variables, class attributes, and functions are stored in the <code class="xref py py-attr docutils literal notranslate">__annotations__</code> special attribute of modules, classes, and functions, respectively. See <a class="reference internal" href="#term-variable-annotation">variable annotation</a>, <a class="reference internal" href="#term-function-annotation">function annotation</a>, <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-0526/">PEP 526</a>, which describe this functionality. Also see <a class="reference internal" href="howto/annotations.html#annotations-howto">Annotations Best Practices</a> for best practices on working with annotations. </dd> <dt id="term-argument">argument<a class="headerlink" href="#term-argument" title="Link to this term">¶</a></dt><dd>A value passed to a <a class="reference internal" href="#term-function">function</a> (or <a class="reference internal" href="#term-method">method</a>) when calling the function. There are two kinds of argument: <ul> <li>keyword argument: an argument preceded by an identifier (e.g. <code class="docutils literal notranslate">name=</code>) in a function call or passed as a value in a dictionary preceded by <code class="docutils literal notranslate">**</code>. For example, <code class="docutils literal notranslate">3</code> and <code class="docutils literal notranslate">5</code> are both keyword arguments in the following calls to <a class="reference internal" href="library/functions.html#complex" title="complex"><code class="xref py py-func docutils literal notranslate">complex()</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>complex(real=3, imag=5) complex(**{'real': 3, 'imag': 5}) </pre></div> </div> </li> <li>positional argument: an argument that is not a keyword argument. Positional arguments can appear at the beginning of an argument list and/or be passed as elements of an <a class="reference internal" href="#term-iterable">iterable</a> preceded by <code class="docutils literal notranslate">*</code>. For example, <code class="docutils literal notranslate">3</code> and <code class="docutils literal notranslate">5</code> are both positional arguments in the following calls: <div class="highlight-python3 notranslate"><div class="highlight"><pre>complex(3, 5) complex(*(3, 5)) </pre></div> </div> </li> </ul> Arguments are assigned to the named local variables in a function body. See the <a class="reference internal" href="reference/expressions.html#calls">Calls</a> section for the rules governing this assignment. Syntactically, any expression can be used to represent an argument; the evaluated value is assigned to the local variable. See also the <a class="reference internal" href="#term-parameter">parameter</a> glossary entry, the FAQ question on <a class="reference internal" href="faq/programming.html#faq-argument-vs-parameter">the difference between arguments and parameters</a>, and <a class="pep reference external" href="https://peps.python.org/pep-0362/">PEP 362</a>. </dd> <dt id="term-asynchronous-context-manager">asynchronous context manager<a class="headerlink" href="#term-asynchronous-context-manager" title="Link to this term">¶</a></dt><dd>An object which controls the environment seen in an <a class="reference internal" href="reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate">async with</code></a> statement by defining <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> and <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> methods. Introduced by <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a>. </dd> <dt id="term-asynchronous-generator">asynchronous generator<a class="headerlink" href="#term-asynchronous-generator" title="Link to this term">¶</a></dt><dd>A function which returns an <a class="reference internal" href="#term-asynchronous-generator-iterator">asynchronous generator iterator</a>. It looks like a coroutine function defined with <a class="reference internal" href="reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate">async def</code></a> except that it contains <a class="reference internal" href="reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> expressions for producing a series of values usable in an <a class="reference internal" href="reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a> loop. Usually refers to an asynchronous generator function, but may refer to an asynchronous generator iterator in some contexts. In cases where the intended meaning isn’t clear, using the full terms avoids ambiguity. An asynchronous generator function may contain <a class="reference internal" href="reference/expressions.html#await"><code class="xref std std-keyword docutils literal notranslate">await</code></a> expressions as well as <a class="reference internal" href="reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a>, and <a class="reference internal" href="reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate">async with</code></a> statements. </dd> <dt id="term-asynchronous-generator-iterator">asynchronous generator iterator<a class="headerlink" href="#term-asynchronous-generator-iterator" title="Link to this term">¶</a></dt><dd>An object created by a <a class="reference internal" href="#term-asynchronous-generator">asynchronous generator</a> function. This is an <a class="reference internal" href="#term-asynchronous-iterator">asynchronous iterator</a> which when called using the <a class="reference internal" href="reference/datamodel.html#object.__anext__" title="object.__anext__"><code class="xref py py-meth docutils literal notranslate">__anext__()</code></a> method returns an awaitable object which will execute the body of the asynchronous generator function until the next <a class="reference internal" href="reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> expression. Each <a class="reference internal" href="reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the asynchronous generator iterator effectively resumes with another awaitable returned by <a class="reference internal" href="reference/datamodel.html#object.__anext__" title="object.__anext__"><code class="xref py py-meth docutils literal notranslate">__anext__()</code></a>, it picks up where it left off. See <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a> and <a class="pep reference external" href="https://peps.python.org/pep-0525/">PEP 525</a>. </dd> <dt id="term-asynchronous-iterable">asynchronous iterable<a class="headerlink" href="#term-asynchronous-iterable" title="Link to this term">¶</a></dt><dd>An object, that can be used in an <a class="reference internal" href="reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a> statement. Must return an <a class="reference internal" href="#term-asynchronous-iterator">asynchronous iterator</a> from its <a class="reference internal" href="reference/datamodel.html#object.__aiter__" title="object.__aiter__"><code class="xref py py-meth docutils literal notranslate">__aiter__()</code></a> method. Introduced by <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a>. </dd> <dt id="term-asynchronous-iterator">asynchronous iterator<a class="headerlink" href="#term-asynchronous-iterator" title="Link to this term">¶</a></dt><dd>An object that implements the <a class="reference internal" href="reference/datamodel.html#object.__aiter__" title="object.__aiter__"><code class="xref py py-meth docutils literal notranslate">__aiter__()</code></a> and <a class="reference internal" href="reference/datamodel.html#object.__anext__" title="object.__anext__"><code class="xref py py-meth docutils literal notranslate">__anext__()</code></a> methods. <a class="reference internal" href="reference/datamodel.html#object.__anext__" title="object.__anext__"><code class="xref py py-meth docutils literal notranslate">__anext__()</code></a> must return an <a class="reference internal" href="#term-awaitable">awaitable</a> object. <a class="reference internal" href="reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a> resolves the awaitables returned by an asynchronous iterator’s <a class="reference internal" href="reference/datamodel.html#object.__anext__" title="object.__anext__"><code class="xref py py-meth docutils literal notranslate">__anext__()</code></a> method until it raises a <a class="reference internal" href="library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate">StopAsyncIteration</code></a> exception. Introduced by <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a>. </dd> <dt id="term-attribute">attribute<a class="headerlink" href="#term-attribute" title="Link to this term">¶</a></dt><dd>A value associated with an object which is usually referenced by name using dotted expressions. For example, if an object o has an attribute a it would be referenced as o.a. It is possible to give an object an attribute whose name is not an identifier as defined by <a class="reference internal" href="reference/lexical_analysis.html#identifiers">Identifiers and keywords</a>, for example using <a class="reference internal" href="library/functions.html#setattr" title="setattr"><code class="xref py py-func docutils literal notranslate">setattr()</code></a>, if the object allows it. Such an attribute will not be accessible using a dotted expression, and would instead need to be retrieved with <a class="reference internal" href="library/functions.html#getattr" title="getattr"><code class="xref py py-func docutils literal notranslate">getattr()</code></a>. </dd> <dt id="term-awaitable">awaitable<a class="headerlink" href="#term-awaitable" title="Link to this term">¶</a></dt><dd>An object that can be used in an <a class="reference internal" href="reference/expressions.html#await"><code class="xref std std-keyword docutils literal notranslate">await</code></a> expression. Can be a <a class="reference internal" href="#term-coroutine">coroutine</a> or an object with an <a class="reference internal" href="reference/datamodel.html#object.__await__" title="object.__await__"><code class="xref py py-meth docutils literal notranslate">__await__()</code></a> method. See also <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a>. </dd> <dt id="term-BDFL">BDFL<a class="headerlink" href="#term-BDFL" title="Link to this term">¶</a></dt><dd>Benevolent Dictator For Life, a.k.a. <a class="reference external" href="https://gvanrossum.github.io/">Guido van Rossum</a>, Python’s creator. </dd> <dt id="term-binary-file">binary file<a class="headerlink" href="#term-binary-file" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="#term-file-object">file object</a> able to read and write <a class="reference internal" href="#term-bytes-like-object">bytes-like objects</a>. Examples of binary files are files opened in binary mode (<code class="docutils literal notranslate">'rb'</code>, <code class="docutils literal notranslate">'wb'</code> or <code class="docutils literal notranslate">'rb+'</code>), <a class="reference internal" href="library/sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate">sys.stdin.buffer</code></a>, <a class="reference internal" href="library/sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate">sys.stdout.buffer</code></a>, and instances of <a class="reference internal" href="library/io.html#io.BytesIO" title="io.BytesIO"><code class="xref py py-class docutils literal notranslate">io.BytesIO</code></a> and <a class="reference internal" href="library/gzip.html#gzip.GzipFile" title="gzip.GzipFile"><code class="xref py py-class docutils literal notranslate">gzip.GzipFile</code></a>. See also <a class="reference internal" href="#term-text-file">text file</a> for a file object able to read and write <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> objects. </dd> <dt id="term-borrowed-reference">borrowed reference<a class="headerlink" href="#term-borrowed-reference" title="Link to this term">¶</a></dt><dd>In Python’s C API, a borrowed reference is a reference to an object, where the code using the object does not own the reference. It becomes a dangling pointer if the object is destroyed. For example, a garbage collection can remove the last <a class="reference internal" href="#term-strong-reference">strong reference</a> to the object and so destroy it. Calling <a class="reference internal" href="c-api/refcounting.html#c.Py_INCREF" title="Py_INCREF"><code class="xref c c-func docutils literal notranslate">Py_INCREF()</code></a> on the <a class="reference internal" href="#term-borrowed-reference">borrowed reference</a> is recommended to convert it to a <a class="reference internal" href="#term-strong-reference">strong reference</a> in-place, except when the object cannot be destroyed before the last usage of the borrowed reference. The <a class="reference internal" href="c-api/refcounting.html#c.Py_NewRef" title="Py_NewRef"><code class="xref c c-func docutils literal notranslate">Py_NewRef()</code></a> function can be used to create a new <a class="reference internal" href="#term-strong-reference">strong reference</a>. </dd> <dt id="term-bytes-like-object">bytes-like object<a class="headerlink" href="#term-bytes-like-object" title="Link to this term">¶</a></dt><dd>An object that supports the <a class="reference internal" href="c-api/buffer.html#bufferobjects">Buffer Protocol</a> and can export a C-<a class="reference internal" href="#term-contiguous">contiguous</a> buffer. This includes all <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>, <a class="reference internal" href="library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate">bytearray</code></a>, and <a class="reference internal" href="library/array.html#array.array" title="array.array"><code class="xref py py-class docutils literal notranslate">array.array</code></a> objects, as well as many common <a class="reference internal" href="library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> objects. Bytes-like objects can be used for various operations that work with binary data; these include compression, saving to a binary file, and sending over a socket. Some operations need the binary data to be mutable. The documentation often refers to these as “read-write bytes-like objects”. Example mutable buffer objects include <a class="reference internal" href="library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate">bytearray</code></a> and a <a class="reference internal" href="library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> of a <a class="reference internal" href="library/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate">bytearray</code></a>. Other operations require the binary data to be stored in immutable objects (“read-only bytes-like objects”); examples of these include <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> and a <a class="reference internal" href="library/stdtypes.html#memoryview" title="memoryview"><code class="xref py py-class docutils literal notranslate">memoryview</code></a> of a <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> object. </dd> <dt id="term-bytecode">bytecode<a class="headerlink" href="#term-bytecode" title="Link to this term">¶</a></dt><dd>Python source code is compiled into bytecode, the internal representation of a Python program in the CPython interpreter. The bytecode is also cached in <code class="docutils literal notranslate">.pyc</code> files so that executing the same file is faster the second time (recompilation from source to bytecode can be avoided). This “intermediate language” is said to run on a <a class="reference internal" href="#term-virtual-machine">virtual machine</a> that executes the machine code corresponding to each bytecode. Do note that bytecodes are not expected to work between different Python virtual machines, nor to be stable between Python releases. A list of bytecode instructions can be found in the documentation for <a class="reference internal" href="library/dis.html#bytecodes">the dis module</a>. </dd> <dt id="term-callable">callable<a class="headerlink" href="#term-callable" title="Link to this term">¶</a></dt><dd>A callable is an object that can be called, possibly with a set of arguments (see <a class="reference internal" href="#term-argument">argument</a>), with the following syntax: <div class="highlight-python3 notranslate"><div class="highlight"><pre>callable(argument1, argument2, argumentN) </pre></div> </div> A <a class="reference internal" href="#term-function">function</a>, and by extension a <a class="reference internal" href="#term-method">method</a>, is a callable. An instance of a class that implements the <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 is also a callable. </dd> <dt id="term-callback">callback<a class="headerlink" href="#term-callback" title="Link to this term">¶</a></dt><dd>A subroutine function which is passed as an argument to be executed at some point in the future. </dd> <dt id="term-class">class<a class="headerlink" href="#term-class" title="Link to this term">¶</a></dt><dd>A template for creating user-defined objects. Class definitions normally contain method definitions which operate on instances of the class. </dd> <dt id="term-class-variable">class variable<a class="headerlink" href="#term-class-variable" title="Link to this term">¶</a></dt><dd>A variable defined in a class and intended to be modified only at class level (i.e., not in an instance of the class). </dd> <dt id="term-closure-variable">closure variable<a class="headerlink" href="#term-closure-variable" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="#term-free-variable">free variable</a> referenced from a <a class="reference internal" href="#term-nested-scope">nested scope</a> that is defined in an outer scope rather than being resolved at runtime from the globals or builtin namespaces. May be explicitly defined with the <a class="reference internal" href="reference/simple_stmts.html#nonlocal"><code class="xref std std-keyword docutils literal notranslate">nonlocal</code></a> keyword to allow write access, or implicitly defined if the variable is only being read. For example, in the <code class="docutils literal notranslate">inner</code> function in the following code, both <code class="docutils literal notranslate">x</code> and <code class="docutils literal notranslate">print</code> are <a class="reference internal" href="#term-free-variable">free variables</a>, but only <code class="docutils literal notranslate">x</code> is a closure variable: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def outer(): x = 0 def inner(): nonlocal x x += 1 print(x) return inner </pre></div> </div> Due to the <a class="reference internal" href="reference/datamodel.html#codeobject.co_freevars" title="codeobject.co_freevars"><code class="xref py py-attr docutils literal notranslate">codeobject.co_freevars</code></a> attribute (which, despite its name, only includes the names of closure variables rather than listing all referenced free variables), the more general <a class="reference internal" href="#term-free-variable">free variable</a> term is sometimes used even when the intended meaning is to refer specifically to closure variables. </dd> <dt id="term-complex-number">complex number<a class="headerlink" href="#term-complex-number" title="Link to this term">¶</a></dt><dd>An extension of the familiar real number system in which all numbers are expressed as a sum of a real part and an imaginary part. Imaginary numbers are real multiples of the imaginary unit (the square root of <code class="docutils literal notranslate">-1</code>), often written <code class="docutils literal notranslate">i</code> in mathematics or <code class="docutils literal notranslate">j</code> in engineering. Python has built-in support for complex numbers, which are written with this latter notation; the imaginary part is written with a <code class="docutils literal notranslate">j</code> suffix, e.g., <code class="docutils literal notranslate">3+1j</code>. To get access to complex equivalents of the <a class="reference internal" href="library/math.html#module-math" title="math: Mathematical functions (sin() etc.)."><code class="xref py py-mod docutils literal notranslate">math</code></a> module, use <a class="reference internal" href="library/cmath.html#module-cmath" title="cmath: Mathematical functions for complex numbers."><code class="xref py py-mod docutils literal notranslate">cmath</code></a>. Use of complex numbers is a fairly advanced mathematical feature. If you’re not aware of a need for them, it’s almost certain you can safely ignore them. </dd> <dt id="term-context">context<a class="headerlink" href="#term-context" title="Link to this term">¶</a></dt><dd>This term has different meanings depending on where and how it is used. Some common meanings: <ul class="simple"> <li>The temporary state or environment established by a <a class="reference internal" href="#term-context-manager">context manager</a> via a <a class="reference internal" href="reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement.</li> <li>The collection of keyvalue bindings associated with a particular <a class="reference internal" href="library/contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate">contextvars.Context</code></a> object and accessed via <a class="reference internal" href="library/contextvars.html#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate">ContextVar</code></a> objects. Also see <a class="reference internal" href="#term-context-variable">context variable</a>.</li> <li>A <a class="reference internal" href="library/contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate">contextvars.Context</code></a> object. Also see <a class="reference internal" href="#term-current-context">current context</a>.</li> </ul> </dd> <dt id="term-context-management-protocol">context management protocol<a class="headerlink" href="#term-context-management-protocol" title="Link to this term">¶</a></dt><dd>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> and <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> methods called by the <a class="reference internal" href="reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement. See <a class="pep reference external" href="https://peps.python.org/pep-0343/">PEP 343</a>. </dd> <dt id="term-context-manager">context manager<a class="headerlink" href="#term-context-manager" title="Link to this term">¶</a></dt><dd>An object which implements the <a class="reference internal" href="#term-context-management-protocol">context management protocol</a> and controls the environment seen in a <a class="reference internal" href="reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement. See <a class="pep reference external" href="https://peps.python.org/pep-0343/">PEP 343</a>. </dd> <dt id="term-context-variable">context variable<a class="headerlink" href="#term-context-variable" title="Link to this term">¶</a></dt><dd>A variable whose value depends on which context is the <a class="reference internal" href="#term-current-context">current context</a>. Values are accessed via <a class="reference internal" href="library/contextvars.html#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate">contextvars.ContextVar</code></a> objects. Context variables are primarily used to isolate state between concurrent asynchronous tasks. </dd> <dt id="term-contiguous">contiguous<a class="headerlink" href="#term-contiguous" title="Link to this term">¶</a></dt><dd>A buffer is considered contiguous exactly if it is either C-contiguous or Fortran contiguous. Zero-dimensional buffers are C and Fortran contiguous. In one-dimensional arrays, the items must be laid out in memory next to each other, in order of increasing indexes starting from zero. In multidimensional C-contiguous arrays, the last index varies the fastest when visiting items in order of memory address. However, in Fortran contiguous arrays, the first index varies the fastest. </dd> <dt id="term-coroutine">coroutine<a class="headerlink" href="#term-coroutine" title="Link to this term">¶</a></dt><dd>Coroutines are a more generalized form of subroutines. Subroutines are entered at one point and exited at another point. Coroutines can be entered, exited, and resumed at many different points. They can be implemented with the <a class="reference internal" href="reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate">async def</code></a> statement. See also <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a>. </dd> <dt id="term-coroutine-function">coroutine function<a class="headerlink" href="#term-coroutine-function" title="Link to this term">¶</a></dt><dd>A function which returns a <a class="reference internal" href="#term-coroutine">coroutine</a> object. A coroutine function may be defined with the <a class="reference internal" href="reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate">async def</code></a> statement, and may contain <a class="reference internal" href="reference/expressions.html#await"><code class="xref std std-keyword docutils literal notranslate">await</code></a>, <a class="reference internal" href="reference/compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate">async for</code></a>, and <a class="reference internal" href="reference/compound_stmts.html#async-with"><code class="xref std std-keyword docutils literal notranslate">async with</code></a> keywords. These were introduced by <a class="pep reference external" href="https://peps.python.org/pep-0492/">PEP 492</a>. </dd> <dt id="term-CPython">CPython<a class="headerlink" href="#term-CPython" title="Link to this term">¶</a></dt><dd>The canonical implementation of the Python programming language, as distributed on <a class="reference external" href="https://www.python.org">python.org</a>. The term “CPython” is used when necessary to distinguish this implementation from others such as Jython or IronPython. </dd> <dt id="term-current-context">current context<a class="headerlink" href="#term-current-context" title="Link to this term">¶</a></dt><dd>The <a class="reference internal" href="#term-context">context</a> (<a class="reference internal" href="library/contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate">contextvars.Context</code></a> object) that is currently used by <a class="reference internal" href="library/contextvars.html#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate">ContextVar</code></a> objects to access (get or set) the values of <a class="reference internal" href="#term-context-variable">context variables</a>. Each thread has its own current context. Frameworks for executing asynchronous tasks (see <a class="reference internal" href="library/asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate">asyncio</code></a>) associate each task with a context which becomes the current context whenever the task starts or resumes execution. </dd> <dt id="term-decorator">decorator<a class="headerlink" href="#term-decorator" title="Link to this term">¶</a></dt><dd>A function returning another function, usually applied as a function transformation using the <code class="docutils literal notranslate">@wrapper</code> syntax. Common examples for decorators are <a class="reference internal" href="library/functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate">classmethod()</code></a> and <a class="reference internal" href="library/functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate">staticmethod()</code></a>. The decorator syntax is merely syntactic sugar, the following two function definitions are semantically equivalent: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def f(arg): ... f = staticmethod(f) @staticmethod def f(arg): ... </pre></div> </div> The same concept exists for classes, but is less commonly used there. See the documentation for <a class="reference internal" href="reference/compound_stmts.html#function">function definitions</a> and <a class="reference internal" href="reference/compound_stmts.html#class">class definitions</a> for more about decorators. </dd> <dt id="term-descriptor">descriptor<a class="headerlink" href="#term-descriptor" title="Link to this term">¶</a></dt><dd>Any object which defines the methods <a class="reference internal" href="reference/datamodel.html#object.__get__" title="object.__get__"><code class="xref py py-meth docutils literal notranslate">__get__()</code></a>, <a class="reference internal" href="reference/datamodel.html#object.__set__" title="object.__set__"><code class="xref py py-meth docutils literal notranslate">__set__()</code></a>, or <a class="reference internal" href="reference/datamodel.html#object.__delete__" title="object.__delete__"><code class="xref py py-meth docutils literal notranslate">__delete__()</code></a>. When a class attribute is a descriptor, its special binding behavior is triggered upon attribute lookup. Normally, using a.b to get, set or delete an attribute looks up the object named b in the class dictionary for a, but if b is a descriptor, the respective descriptor method gets called. Understanding descriptors is a key to a deep understanding of Python because they are the basis for many features including functions, methods, properties, class methods, static methods, and reference to super classes. For more information about descriptors’ methods, see <a class="reference internal" href="reference/datamodel.html#descriptors">Implementing Descriptors</a> or the <a class="reference internal" href="howto/descriptor.html#descriptorhowto">Descriptor How To Guide</a>. </dd> <dt id="term-dictionary">dictionary<a class="headerlink" href="#term-dictionary" title="Link to this term">¶</a></dt><dd>An associative array, where arbitrary keys are mapped to values. The keys can be any object with <a class="reference internal" href="reference/datamodel.html#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> and <a class="reference internal" href="reference/datamodel.html#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> methods. Called a hash in Perl. </dd> <dt id="term-dictionary-comprehension">dictionary comprehension<a class="headerlink" href="#term-dictionary-comprehension" title="Link to this term">¶</a></dt><dd>A compact way to process all or part of the elements in an iterable and return a dictionary with the results. <code class="docutils literal notranslate">results = {n: n ** 2 for n in range(10)}</code> generates a dictionary containing key <code class="docutils literal notranslate">n</code> mapped to value <code class="docutils literal notranslate">n ** 2</code>. See <a class="reference internal" href="reference/expressions.html#comprehensions">Displays for lists, sets and dictionaries</a>. </dd> <dt id="term-dictionary-view">dictionary view<a class="headerlink" href="#term-dictionary-view" title="Link to this term">¶</a></dt><dd>The objects returned from <a class="reference internal" href="library/stdtypes.html#dict.keys" title="dict.keys"><code class="xref py py-meth docutils literal notranslate">dict.keys()</code></a>, <a class="reference internal" href="library/stdtypes.html#dict.values" title="dict.values"><code class="xref py py-meth docutils literal notranslate">dict.values()</code></a>, and <a class="reference internal" href="library/stdtypes.html#dict.items" title="dict.items"><code class="xref py py-meth docutils literal notranslate">dict.items()</code></a> are called dictionary views. They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes. To force the dictionary view to become a full list use <code class="docutils literal notranslate">list(dictview)</code>. See <a class="reference internal" href="library/stdtypes.html#dict-views">Dictionary view objects</a>. </dd> <dt id="term-docstring">docstring<a class="headerlink" href="#term-docstring" title="Link to this term">¶</a></dt><dd>A string literal which appears as the first expression in a class, function or module. While ignored when the suite is executed, it is recognized by the compiler and put into the <a class="reference internal" href="library/stdtypes.html#definition.__doc__" title="definition.__doc__"><code class="xref py py-attr docutils literal notranslate">__doc__</code></a> attribute of the enclosing class, function or module. Since it is available via introspection, it is the canonical place for documentation of the object. </dd> <dt id="term-duck-typing">duck-typing<a class="headerlink" href="#term-duck-typing" title="Link to this term">¶</a></dt><dd>A programming style which does not look at an object’s type to determine if it has the right interface; instead, the method or attribute is simply called or used (“If it looks like a duck and quacks like a duck, it must be a duck.”) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using <a class="reference internal" href="library/functions.html#type" title="type"><code class="xref py py-func docutils literal notranslate">type()</code></a> or <a class="reference internal" href="library/functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a>. (Note, however, that duck-typing can be complemented with <a class="reference internal" href="#term-abstract-base-class">abstract base classes</a>.) Instead, it typically employs <a class="reference internal" href="library/functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate">hasattr()</code></a> tests or <a class="reference internal" href="#term-EAFP">EAFP</a> programming. </dd> <dt id="term-EAFP">EAFP<a class="headerlink" href="#term-EAFP" title="Link to this term">¶</a></dt><dd>Easier to ask for forgiveness than permission. This common Python coding style assumes the existence of valid keys or attributes and catches exceptions if the assumption proves false. This clean and fast style is characterized by the presence of many <a class="reference internal" href="reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate">try</code></a> and <a class="reference internal" href="reference/compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate">except</code></a> statements. The technique contrasts with the <a class="reference internal" href="#term-LBYL">LBYL</a> style common to many other languages such as C. </dd> <dt id="term-expression">expression<a class="headerlink" href="#term-expression" title="Link to this term">¶</a></dt><dd>A piece of syntax which can be evaluated to some value. In other words, an expression is an accumulation of expression elements like literals, names, attribute access, operators or function calls which all return a value. In contrast to many other languages, not all language constructs are expressions. There are also <a class="reference internal" href="#term-statement">statement</a>s which cannot be used as expressions, such as <a class="reference internal" href="reference/compound_stmts.html#while"><code class="xref std std-keyword docutils literal notranslate">while</code></a>. Assignments are also statements, not expressions. </dd> <dt id="term-extension-module">extension module<a class="headerlink" href="#term-extension-module" title="Link to this term">¶</a></dt><dd>A module written in C or C++, using Python’s C API to interact with the core and with user code. </dd> <dt id="term-f-string">f-string<a class="headerlink" href="#term-f-string" title="Link to this term">¶</a></dt><dd>String literals prefixed with <code class="docutils literal notranslate">'f'</code> or <code class="docutils literal notranslate">'F'</code> are commonly called “f-strings” which is short for <a class="reference internal" href="reference/lexical_analysis.html#f-strings">formatted string literals</a>. See also <a class="pep reference external" href="https://peps.python.org/pep-0498/">PEP 498</a>. </dd> <dt id="term-file-object">file object<a class="headerlink" href="#term-file-object" title="Link to this term">¶</a></dt><dd>An object exposing a file-oriented API (with methods such as <code class="xref py py-meth docutils literal notranslate">read()</code> or <code class="xref py py-meth docutils literal notranslate">write()</code>) to an underlying resource. Depending on the way it was created, a file object can mediate access to a real on-disk file or to another type of storage or communication device (for example standard input/output, in-memory buffers, sockets, pipes, etc.). File objects are also called file-like objects or streams. There are actually three categories of file objects: raw <a class="reference internal" href="#term-binary-file">binary files</a>, buffered <a class="reference internal" href="#term-binary-file">binary files</a> and <a class="reference internal" href="#term-text-file">text files</a>. Their interfaces are defined in the <a class="reference internal" href="library/io.html#module-io" title="io: Core tools for working with streams."><code class="xref py py-mod docutils literal notranslate">io</code></a> module. The canonical way to create a file object is by using the <a class="reference internal" href="library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> function. </dd> <dt id="term-file-like-object">file-like object<a class="headerlink" href="#term-file-like-object" title="Link to this term">¶</a></dt><dd>A synonym for <a class="reference internal" href="#term-file-object">file object</a>. </dd> <dt id="term-filesystem-encoding-and-error-handler">filesystem encoding and error handler<a class="headerlink" href="#term-filesystem-encoding-and-error-handler" title="Link to this term">¶</a></dt><dd>Encoding and error handler used by Python to decode bytes from the operating system and encode Unicode to the operating system. The filesystem encoding must guarantee to successfully decode all bytes below 128. If the file system encoding fails to provide this guarantee, API functions can raise <a class="reference internal" href="library/exceptions.html#UnicodeError" title="UnicodeError"><code class="xref py py-exc docutils literal notranslate">UnicodeError</code></a>. The <a class="reference internal" href="library/sys.html#sys.getfilesystemencoding" title="sys.getfilesystemencoding"><code class="xref py py-func docutils literal notranslate">sys.getfilesystemencoding()</code></a> and <a class="reference internal" href="library/sys.html#sys.getfilesystemencodeerrors" title="sys.getfilesystemencodeerrors"><code class="xref py py-func docutils literal notranslate">sys.getfilesystemencodeerrors()</code></a> functions can be used to get the filesystem encoding and error handler. The <a class="reference internal" href="#term-filesystem-encoding-and-error-handler">filesystem encoding and error handler</a> are configured at Python startup by the <a class="reference internal" href="c-api/init_config.html#c.PyConfig_Read" title="PyConfig_Read"><code class="xref c c-func docutils literal notranslate">PyConfig_Read()</code></a> function: see <a class="reference internal" href="c-api/init_config.html#c.PyConfig.filesystem_encoding" title="PyConfig.filesystem_encoding"><code class="xref c c-member docutils literal notranslate">filesystem_encoding</code></a> and <a class="reference internal" href="c-api/init_config.html#c.PyConfig.filesystem_errors" title="PyConfig.filesystem_errors"><code class="xref c c-member docutils literal notranslate">filesystem_errors</code></a> members of <a class="reference internal" href="c-api/init_config.html#c.PyConfig" title="PyConfig"><code class="xref c c-type docutils literal notranslate">PyConfig</code></a>. See also the <a class="reference internal" href="#term-locale-encoding">locale encoding</a>. </dd> <dt id="term-finder">finder<a class="headerlink" href="#term-finder" title="Link to this term">¶</a></dt><dd>An object that tries to find the <a class="reference internal" href="#term-loader">loader</a> for a module that is being imported. There are two types of finder: <a class="reference internal" href="#term-meta-path-finder">meta path finders</a> for use with <a class="reference internal" href="library/sys.html#sys.meta_path" title="sys.meta_path"><code class="xref py py-data docutils literal notranslate">sys.meta_path</code></a>, and <a class="reference internal" href="#term-path-entry-finder">path entry finders</a> for use with <a class="reference internal" href="library/sys.html#sys.path_hooks" title="sys.path_hooks"><code class="xref py py-data docutils literal notranslate">sys.path_hooks</code></a>. See <a class="reference internal" href="reference/import.html#finders-and-loaders">Finders and loaders</a> and <a class="reference internal" href="library/importlib.html#module-importlib" title="importlib: The implementation of the import machinery."><code class="xref py py-mod docutils literal notranslate">importlib</code></a> for much more detail. </dd> <dt id="term-floor-division">floor division<a class="headerlink" href="#term-floor-division" title="Link to this term">¶</a></dt><dd>Mathematical division that rounds down to nearest integer. The floor division operator is <code class="docutils literal notranslate">//</code>. For example, the expression <code class="docutils literal notranslate">11 // 4</code> evaluates to <code class="docutils literal notranslate">2</code> in contrast to the <code class="docutils literal notranslate">2.75</code> returned by float true division. Note that <code class="docutils literal notranslate">(-11) // 4</code> is <code class="docutils literal notranslate">-3</code> because that is <code class="docutils literal notranslate">-2.75</code> rounded downward. See <a class="pep reference external" href="https://peps.python.org/pep-0238/">PEP 238</a>. </dd> <dt id="term-free-threading">free threading<a class="headerlink" href="#term-free-threading" title="Link to this term">¶</a></dt><dd>A threading model where multiple threads can run Python bytecode simultaneously within the same interpreter. This is in contrast to the <a class="reference internal" href="#term-global-interpreter-lock">global interpreter lock</a> which allows only one thread to execute Python bytecode at a time. See <a class="pep reference external" href="https://peps.python.org/pep-0703/">PEP 703</a>. </dd> <dt id="term-free-variable">free variable<a class="headerlink" href="#term-free-variable" title="Link to this term">¶</a></dt><dd>Formally, as defined in the <a class="reference internal" href="reference/executionmodel.html#bind-names">language execution model</a>, a free variable is any variable used in a namespace which is not a local variable in that namespace. See <a class="reference internal" href="#term-closure-variable">closure variable</a> for an example. Pragmatically, due to the name of the <a class="reference internal" href="reference/datamodel.html#codeobject.co_freevars" title="codeobject.co_freevars"><code class="xref py py-attr docutils literal notranslate">codeobject.co_freevars</code></a> attribute, the term is also sometimes used as a synonym for <a class="reference internal" href="#term-closure-variable">closure variable</a>. </dd> <dt id="term-function">function<a class="headerlink" href="#term-function" title="Link to this term">¶</a></dt><dd>A series of statements which returns some value to a caller. It can also be passed zero or more <a class="reference internal" href="#term-argument">arguments</a> which may be used in the execution of the body. See also <a class="reference internal" href="#term-parameter">parameter</a>, <a class="reference internal" href="#term-method">method</a>, and the <a class="reference internal" href="reference/compound_stmts.html#function">Function definitions</a> section. </dd> <dt id="term-function-annotation">function annotation<a class="headerlink" href="#term-function-annotation" title="Link to this term">¶</a></dt><dd>An <a class="reference internal" href="#term-annotation">annotation</a> of a function parameter or return value. Function annotations are usually used for <a class="reference internal" href="#term-type-hint">type hints</a>: for example, this function is expected to take two <a class="reference internal" href="library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> arguments and is also expected to have an <a class="reference internal" href="library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> return value: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def sum_two_numbers(a: int, b: int) -> int: return a + b </pre></div> </div> Function annotation syntax is explained in section <a class="reference internal" href="reference/compound_stmts.html#function">Function definitions</a>. See <a class="reference internal" href="#term-variable-annotation">variable annotation</a> and <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a>, which describe this functionality. Also see <a class="reference internal" href="howto/annotations.html#annotations-howto">Annotations Best Practices</a> for best practices on working with annotations. </dd> <dt id="term-__future__">__future__<a class="headerlink" href="#term-__future__" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="reference/simple_stmts.html#future">future statement</a>, <code class="docutils literal notranslate">from __future__ import <feature></code>, directs the compiler to compile the current module using syntax or semantics that will become standard in a future release of Python. The <a class="reference internal" href="library/__future__.html#module-__future__" title="__future__: Future statement definitions"><code class="xref py py-mod docutils literal notranslate">__future__</code></a> module documents the possible values of feature. By importing this module and evaluating its variables, you can see when a new feature was first added to the language and when it will (or did) become the default: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> import __future__ >>> __future__.division _Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192) </pre></div> </div> </dd> <dt id="term-garbage-collection">garbage collection<a class="headerlink" href="#term-garbage-collection" title="Link to this term">¶</a></dt><dd>The process of freeing memory when it is not used anymore. Python performs garbage collection via reference counting and a cyclic garbage collector that is able to detect and break reference cycles. The garbage collector can be controlled using the <a class="reference internal" href="library/gc.html#module-gc" title="gc: Interface to the cycle-detecting garbage collector."><code class="xref py py-mod docutils literal notranslate">gc</code></a> module. </dd> <dt id="term-generator">generator<a class="headerlink" href="#term-generator" title="Link to this term">¶</a></dt><dd>A function which returns a <a class="reference internal" href="#term-generator-iterator">generator iterator</a>. It looks like a normal function except that it contains <a class="reference internal" href="reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> expressions for producing a series of values usable in a for-loop or that can be retrieved one at a time with the <a class="reference internal" href="library/functions.html#next" title="next"><code class="xref py py-func docutils literal notranslate">next()</code></a> function. Usually refers to a generator function, but may refer to a generator iterator in some contexts. In cases where the intended meaning isn’t clear, using the full terms avoids ambiguity. </dd> <dt id="term-generator-iterator">generator iterator<a class="headerlink" href="#term-generator-iterator" title="Link to this term">¶</a></dt><dd>An object created by a <a class="reference internal" href="#term-generator">generator</a> function. Each <a class="reference internal" href="reference/simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate">yield</code></a> temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the generator iterator resumes, it picks up where it left off (in contrast to functions which start fresh on every invocation). </dd> <dt id="term-generator-expression">generator expression<a class="headerlink" href="#term-generator-expression" title="Link to this term">¶</a></dt><dd>An <a class="reference internal" href="#term-expression">expression</a> that returns an <a class="reference internal" href="#term-iterator">iterator</a>. It looks like a normal expression followed by a <code class="xref std std-keyword docutils literal notranslate">for</code> clause defining a loop variable, range, and an optional <code class="xref std std-keyword docutils literal notranslate">if</code> clause. The combined expression generates values for an enclosing function: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> sum(i*i for i in range(10)) # sum of squares 0, 1, 4, ... 81 285 </pre></div> </div> </dd> <dt id="term-generic-function">generic function<a class="headerlink" href="#term-generic-function" title="Link to this term">¶</a></dt><dd>A function composed of multiple functions implementing the same operation for different types. Which implementation should be used during a call is determined by the dispatch algorithm. See also the <a class="reference internal" href="#term-single-dispatch">single dispatch</a> glossary entry, the <a class="reference internal" href="library/functools.html#functools.singledispatch" title="functools.singledispatch"><code class="xref py py-func docutils literal notranslate">functools.singledispatch()</code></a> decorator, and <a class="pep reference external" href="https://peps.python.org/pep-0443/">PEP 443</a>. </dd> <dt id="term-generic-type">generic type<a class="headerlink" href="#term-generic-type" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="#term-type">type</a> that can be parameterized; typically a <a class="reference internal" href="reference/datamodel.html#sequence-types">container class</a> such as <a class="reference internal" href="library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a> or <a class="reference internal" href="library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>. Used for <a class="reference internal" href="#term-type-hint">type hints</a> and <a class="reference internal" href="#term-annotation">annotations</a>. For more details, see <a class="reference internal" href="library/stdtypes.html#types-genericalias">generic alias types</a>, <a class="pep reference external" href="https://peps.python.org/pep-0483/">PEP 483</a>, <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a>, <a class="pep reference external" href="https://peps.python.org/pep-0585/">PEP 585</a>, and the <a class="reference internal" href="library/typing.html#module-typing" title="typing: Support for type hints (see :pep:`484`)."><code class="xref py py-mod docutils literal notranslate">typing</code></a> module. </dd> <dt id="term-GIL">GIL<a class="headerlink" href="#term-GIL" title="Link to this term">¶</a></dt><dd>See <a class="reference internal" href="#term-global-interpreter-lock">global interpreter lock</a>. </dd> <dt id="term-global-interpreter-lock">global interpreter lock<a class="headerlink" href="#term-global-interpreter-lock" title="Link to this term">¶</a></dt><dd>The mechanism used by the <a class="reference internal" href="#term-CPython">CPython</a> interpreter to assure that only one thread executes Python <a class="reference internal" href="#term-bytecode">bytecode</a> at a time. This simplifies the CPython implementation by making the object model (including critical built-in types such as <a class="reference internal" href="library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>) implicitly safe against concurrent access. Locking the entire interpreter makes it easier for the interpreter to be multi-threaded, at the expense of much of the parallelism afforded by multi-processor machines. However, some extension modules, either standard or third-party, are designed so as to release the GIL when doing computationally intensive tasks such as compression or hashing. Also, the GIL is always released when doing I/O. As of Python 3.13, the GIL can be disabled using the <a class="reference internal" href="using/configure.html#cmdoption-disable-gil"><code class="xref std std-option docutils literal notranslate">--disable-gil</code></a> build configuration. After building Python with this option, code must be run with <a class="reference internal" href="using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal notranslate">-X gil=0</code></a> or after setting the <a class="reference internal" href="using/cmdline.html#envvar-PYTHON_GIL"><code class="xref std std-envvar docutils literal notranslate">PYTHON_GIL=0</code></a> environment variable. This feature enables improved performance for multi-threaded applications and makes it easier to use multi-core CPUs efficiently. For more details, see <a class="pep reference external" href="https://peps.python.org/pep-0703/">PEP 703</a>. </dd> <dt id="term-hash-based-pyc">hash-based pyc<a class="headerlink" href="#term-hash-based-pyc" title="Link to this term">¶</a></dt><dd>A bytecode cache file that uses the hash rather than the last-modified time of the corresponding source file to determine its validity. See <a class="reference internal" href="reference/import.html#pyc-invalidation">Cached bytecode invalidation</a>. </dd> <dt id="term-hashable">hashable<a class="headerlink" href="#term-hashable" title="Link to this term">¶</a></dt><dd>An object is hashable if it has a hash value which never changes during its lifetime (it needs a <a class="reference internal" href="reference/datamodel.html#object.__hash__" title="object.__hash__"><code class="xref py py-meth docutils literal notranslate">__hash__()</code></a> method), and can be compared to other objects (it needs an <a class="reference internal" href="reference/datamodel.html#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> method). Hashable objects which compare equal must have the same hash value. Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally. Most of Python’s immutable built-in objects are hashable; mutable containers (such as lists or dictionaries) are not; immutable containers (such as tuples and frozensets) are only hashable if their elements are hashable. Objects which are instances of user-defined classes are hashable by default. They all compare unequal (except with themselves), and their hash value is derived from their <a class="reference internal" href="library/functions.html#id" title="id"><code class="xref py py-func docutils literal notranslate">id()</code></a>. </dd> <dt id="term-IDLE">IDLE<a class="headerlink" href="#term-IDLE" title="Link to this term">¶</a></dt><dd>An Integrated Development and Learning Environment for Python. <a class="reference internal" href="library/idle.html#idle">IDLE</a> is a basic editor and interpreter environment which ships with the standard distribution of Python. </dd> <dt id="term-immortal">immortal<a class="headerlink" href="#term-immortal" title="Link to this term">¶</a></dt><dd>Immortal objects are a CPython implementation detail introduced in <a class="pep reference external" href="https://peps.python.org/pep-0683/">PEP 683</a>. If an object is immortal, its <a class="reference internal" href="#term-reference-count">reference count</a> is never modified, and therefore it is never deallocated while the interpreter is running. For example, <a class="reference internal" href="library/constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a> and <a class="reference internal" href="library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate">None</code></a> are immortal in CPython. </dd> <dt id="term-immutable">immutable<a class="headerlink" href="#term-immutable" title="Link to this term">¶</a></dt><dd>An object with a fixed value. Immutable objects include numbers, strings and tuples. Such an object cannot be altered. A new object has to be created if a different value has to be stored. They play an important role in places where a constant hash value is needed, for example as a key in a dictionary. </dd> <dt id="term-import-path">import path<a class="headerlink" href="#term-import-path" title="Link to this term">¶</a></dt><dd>A list of locations (or <a class="reference internal" href="#term-path-entry">path entries</a>) that are searched by the <a class="reference internal" href="#term-path-based-finder">path based finder</a> for modules to import. During import, this list of locations usually comes from <a class="reference internal" href="library/sys.html#sys.path" title="sys.path"><code class="xref py py-data docutils literal notranslate">sys.path</code></a>, but for subpackages it may also come from the parent package’s <code class="docutils literal notranslate">__path__</code> attribute. </dd> <dt id="term-importing">importing<a class="headerlink" href="#term-importing" title="Link to this term">¶</a></dt><dd>The process by which Python code in one module is made available to Python code in another module. </dd> <dt id="term-importer">importer<a class="headerlink" href="#term-importer" title="Link to this term">¶</a></dt><dd>An object that both finds and loads a module; both a <a class="reference internal" href="#term-finder">finder</a> and <a class="reference internal" href="#term-loader">loader</a> object. </dd> <dt id="term-interactive">interactive<a class="headerlink" href="#term-interactive" title="Link to this term">¶</a></dt><dd>Python has an interactive interpreter which means you can enter statements and expressions at the interpreter prompt, immediately execute them and see their results. Just launch <code class="docutils literal notranslate">python</code> with no arguments (possibly by selecting it from your computer’s main menu). It is a very powerful way to test out new ideas or inspect modules and packages (remember <code class="docutils literal notranslate">help(x)</code>). For more on interactive mode, see <a class="reference internal" href="tutorial/appendix.html#tut-interac">Interactive Mode</a>. </dd> <dt id="term-interpreted">interpreted<a class="headerlink" href="#term-interpreted" title="Link to this term">¶</a></dt><dd>Python is an interpreted language, as opposed to a compiled one, though the distinction can be blurry because of the presence of the bytecode compiler. This means that source files can be run directly without explicitly creating an executable which is then run. Interpreted languages typically have a shorter development/debug cycle than compiled ones, though their programs generally also run more slowly. See also <a class="reference internal" href="#term-interactive">interactive</a>. </dd> <dt id="term-interpreter-shutdown">interpreter shutdown<a class="headerlink" href="#term-interpreter-shutdown" title="Link to this term">¶</a></dt><dd>When asked to shut down, the Python interpreter enters a special phase where it gradually releases all allocated resources, such as modules and various critical internal structures. It also makes several calls to the <a class="reference internal" href="#term-garbage-collection">garbage collector</a>. This can trigger the execution of code in user-defined destructors or weakref callbacks. Code executed during the shutdown phase can encounter various exceptions as the resources it relies on may not function anymore (common examples are library modules or the warnings machinery). The main reason for interpreter shutdown is that the <code class="docutils literal notranslate">__main__</code> module or the script being run has finished executing. </dd> <dt id="term-iterable">iterable<a class="headerlink" href="#term-iterable" title="Link to this term">¶</a></dt><dd>An object capable of returning its members one at a time. Examples of iterables include all sequence types (such as <a class="reference internal" href="library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a>, <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, and <a class="reference internal" href="library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>) and some non-sequence types like <a class="reference internal" href="library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>, <a class="reference internal" href="#term-file-object">file objects</a>, and objects of any classes you define with an <a class="reference internal" href="library/stdtypes.html#iterator.__iter__" title="iterator.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a> method or with a <a class="reference internal" href="reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> method that implements <a class="reference internal" href="#term-sequence">sequence</a> semantics. Iterables can be used in a <a class="reference internal" href="reference/compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate">for</code></a> loop and in many other places where a sequence is needed (<a class="reference internal" href="library/functions.html#zip" title="zip"><code class="xref py py-func docutils literal notranslate">zip()</code></a>, <a class="reference internal" href="library/functions.html#map" title="map"><code class="xref py py-func docutils literal notranslate">map()</code></a>, …). When an iterable object is passed as an argument to the built-in function <a class="reference internal" href="library/functions.html#iter" title="iter"><code class="xref py py-func docutils literal notranslate">iter()</code></a>, it returns an iterator for the object. This iterator is good for one pass over the set of values. When using iterables, it is usually not necessary to call <a class="reference internal" href="library/functions.html#iter" title="iter"><code class="xref py py-func docutils literal notranslate">iter()</code></a> or deal with iterator objects yourself. The <a class="reference internal" href="reference/compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate">for</code></a> statement does that automatically for you, creating a temporary unnamed variable to hold the iterator for the duration of the loop. See also <a class="reference internal" href="#term-iterator">iterator</a>, <a class="reference internal" href="#term-sequence">sequence</a>, and <a class="reference internal" href="#term-generator">generator</a>. </dd> <dt id="term-iterator">iterator<a class="headerlink" href="#term-iterator" title="Link to this term">¶</a></dt><dd>An object representing a stream of data. Repeated calls to the iterator’s <a class="reference internal" href="library/stdtypes.html#iterator.__next__" title="iterator.__next__"><code class="xref py py-meth docutils literal notranslate">__next__()</code></a> method (or passing it to the built-in function <a class="reference internal" href="library/functions.html#next" title="next"><code class="xref py py-func docutils literal notranslate">next()</code></a>) return successive items in the stream. When no more data are available a <a class="reference internal" href="library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a> exception is raised instead. At this point, the iterator object is exhausted and any further calls to its <code class="xref py py-meth docutils literal notranslate">__next__()</code> method just raise <a class="reference internal" href="library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a> again. Iterators are required to have an <a class="reference internal" href="library/stdtypes.html#iterator.__iter__" title="iterator.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a> method that returns the iterator object itself so every iterator is also iterable and may be used in most places where other iterables are accepted. One notable exception is code which attempts multiple iteration passes. A container object (such as a <a class="reference internal" href="library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a>) produces a fresh new iterator each time you pass it to the <a class="reference internal" href="library/functions.html#iter" title="iter"><code class="xref py py-func docutils literal notranslate">iter()</code></a> function or use it in a <a class="reference internal" href="reference/compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate">for</code></a> loop. Attempting this with an iterator will just return the same exhausted iterator object used in the previous iteration pass, making it appear like an empty container. More information can be found in <a class="reference internal" href="library/stdtypes.html#typeiter">Iterator Types</a>. <div class="impl-detail compound"> CPython implementation detail: CPython does not consistently apply the requirement that an iterator define <a class="reference internal" href="library/stdtypes.html#iterator.__iter__" title="iterator.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a>. And also please note that the free-threading CPython does not guarantee the thread-safety of iterator operations. </div> </dd> <dt id="term-key-function">key function<a class="headerlink" href="#term-key-function" title="Link to this term">¶</a></dt><dd>A key function or collation function is a callable that returns a value used for sorting or ordering. For example, <a class="reference internal" href="library/locale.html#locale.strxfrm" title="locale.strxfrm"><code class="xref py py-func docutils literal notranslate">locale.strxfrm()</code></a> is used to produce a sort key that is aware of locale specific sort conventions. A number of tools in Python accept key functions to control how elements are ordered or grouped. They include <a class="reference internal" href="library/functions.html#min" title="min"><code class="xref py py-func docutils literal notranslate">min()</code></a>, <a class="reference internal" href="library/functions.html#max" title="max"><code class="xref py py-func docutils literal notranslate">max()</code></a>, <a class="reference internal" href="library/functions.html#sorted" title="sorted"><code class="xref py py-func docutils literal notranslate">sorted()</code></a>, <a class="reference internal" href="library/stdtypes.html#list.sort" title="list.sort"><code class="xref py py-meth docutils literal notranslate">list.sort()</code></a>, <a class="reference internal" href="library/heapq.html#heapq.merge" title="heapq.merge"><code class="xref py py-func docutils literal notranslate">heapq.merge()</code></a>, <a class="reference internal" href="library/heapq.html#heapq.nsmallest" title="heapq.nsmallest"><code class="xref py py-func docutils literal notranslate">heapq.nsmallest()</code></a>, <a class="reference internal" href="library/heapq.html#heapq.nlargest" title="heapq.nlargest"><code class="xref py py-func docutils literal notranslate">heapq.nlargest()</code></a>, and <a class="reference internal" href="library/itertools.html#itertools.groupby" title="itertools.groupby"><code class="xref py py-func docutils literal notranslate">itertools.groupby()</code></a>. There are several ways to create a key function. For example. the <a class="reference internal" href="library/stdtypes.html#str.lower" title="str.lower"><code class="xref py py-meth docutils literal notranslate">str.lower()</code></a> method can serve as a key function for case insensitive sorts. Alternatively, a key function can be built from a <a class="reference internal" href="reference/expressions.html#lambda"><code class="xref std std-keyword docutils literal notranslate">lambda</code></a> expression such as <code class="docutils literal notranslate">lambda r: (r[0], r[2])</code>. Also, <a class="reference internal" href="library/operator.html#operator.attrgetter" title="operator.attrgetter"><code class="xref py py-func docutils literal notranslate">operator.attrgetter()</code></a>, <a class="reference internal" href="library/operator.html#operator.itemgetter" title="operator.itemgetter"><code class="xref py py-func docutils literal notranslate">operator.itemgetter()</code></a>, and <a class="reference internal" href="library/operator.html#operator.methodcaller" title="operator.methodcaller"><code class="xref py py-func docutils literal notranslate">operator.methodcaller()</code></a> are three key function constructors. See the <a class="reference internal" href="howto/sorting.html#sortinghowto">Sorting HOW TO</a> for examples of how to create and use key functions. </dd> <dt id="term-keyword-argument">keyword argument<a class="headerlink" href="#term-keyword-argument" title="Link to this term">¶</a></dt><dd>See <a class="reference internal" href="#term-argument">argument</a>. </dd> <dt id="term-lambda">lambda<a class="headerlink" href="#term-lambda" title="Link to this term">¶</a></dt><dd>An anonymous inline function consisting of a single <a class="reference internal" href="#term-expression">expression</a> which is evaluated when the function is called. The syntax to create a lambda function is <code class="docutils literal notranslate">lambda [parameters]: expression</code> </dd> <dt id="term-LBYL">LBYL<a class="headerlink" href="#term-LBYL" title="Link to this term">¶</a></dt><dd>Look before you leap. This coding style explicitly tests for pre-conditions before making calls or lookups. This style contrasts with the <a class="reference internal" href="#term-EAFP">EAFP</a> approach and is characterized by the presence of many <a class="reference internal" href="reference/compound_stmts.html#if"><code class="xref std std-keyword docutils literal notranslate">if</code></a> statements. In a multi-threaded environment, the LBYL approach can risk introducing a race condition between “the looking” and “the leaping”. For example, the code, <code class="docutils literal notranslate">if key in mapping: return mapping[key]</code> can fail if another thread removes key from mapping after the test, but before the lookup. This issue can be solved with locks or by using the EAFP approach. </dd> <dt id="term-list">list<a class="headerlink" href="#term-list" title="Link to this term">¶</a></dt><dd>A built-in Python <a class="reference internal" href="#term-sequence">sequence</a>. Despite its name it is more akin to an array in other languages than to a linked list since access to elements is O(1). </dd> <dt id="term-list-comprehension">list comprehension<a class="headerlink" href="#term-list-comprehension" title="Link to this term">¶</a></dt><dd>A compact way to process all or part of the elements in a sequence and return a list with the results. <code class="docutils literal notranslate">result = ['{:#04x}'.format(x) for x in range(256) if x % 2 == 0]</code> generates a list of strings containing even hex numbers (0x..) in the range from 0 to 255. The <a class="reference internal" href="reference/compound_stmts.html#if"><code class="xref std std-keyword docutils literal notranslate">if</code></a> clause is optional. If omitted, all elements in <code class="docutils literal notranslate">range(256)</code> are processed. </dd> <dt id="term-loader">loader<a class="headerlink" href="#term-loader" title="Link to this term">¶</a></dt><dd>An object that loads a module. It must define a method named <code class="xref py py-meth docutils literal notranslate">load_module()</code>. A loader is typically returned by a <a class="reference internal" href="#term-finder">finder</a>. See also: <ul class="simple"> <li><a class="reference internal" href="reference/import.html#finders-and-loaders">Finders and loaders</a></li> <li><a class="reference internal" href="library/importlib.html#importlib.abc.Loader" title="importlib.abc.Loader"><code class="xref py py-class docutils literal notranslate">importlib.abc.Loader</code></a></li> <li><a class="pep reference external" href="https://peps.python.org/pep-0302/">PEP 302</a></li> </ul> </dd> <dt id="term-locale-encoding">locale encoding<a class="headerlink" href="#term-locale-encoding" title="Link to this term">¶</a></dt><dd>On Unix, it is the encoding of the LC_CTYPE locale. It can be set with <a class="reference internal" href="library/locale.html#locale.setlocale" title="locale.setlocale"><code class="xref py py-func docutils literal notranslate">locale.setlocale(locale.LC_CTYPE, new_locale)</code></a>. On Windows, it is the ANSI code page (ex: <code class="docutils literal notranslate">"cp1252"</code>). On Android and VxWorks, Python uses <code class="docutils literal notranslate">"utf-8"</code> as the locale encoding. <a class="reference internal" href="library/locale.html#locale.getencoding" title="locale.getencoding"><code class="xref py py-func docutils literal notranslate">locale.getencoding()</code></a> can be used to get the locale encoding. See also the <a class="reference internal" href="#term-filesystem-encoding-and-error-handler">filesystem encoding and error handler</a>. </dd> <dt id="term-magic-method">magic method<a class="headerlink" href="#term-magic-method" title="Link to this term">¶</a></dt><dd>An informal synonym for <a class="reference internal" href="#term-special-method">special method</a>. </dd> <dt id="term-mapping">mapping<a class="headerlink" href="#term-mapping" title="Link to this term">¶</a></dt><dd>A container object that supports arbitrary key lookups and implements the methods specified in the <a class="reference internal" href="library/collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate">collections.abc.Mapping</code></a> or <a class="reference internal" href="library/collections.abc.html#collections.abc.MutableMapping" title="collections.abc.MutableMapping"><code class="xref py py-class docutils literal notranslate">collections.abc.MutableMapping</code></a> <a class="reference internal" href="library/collections.abc.html#collections-abstract-base-classes">abstract base classes</a>. Examples include <a class="reference internal" href="library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a>, <a class="reference internal" href="library/collections.html#collections.defaultdict" title="collections.defaultdict"><code class="xref py py-class docutils literal notranslate">collections.defaultdict</code></a>, <a class="reference internal" href="library/collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-class docutils literal notranslate">collections.OrderedDict</code></a> and <a class="reference internal" href="library/collections.html#collections.Counter" title="collections.Counter"><code class="xref py py-class docutils literal notranslate">collections.Counter</code></a>. </dd> <dt id="term-meta-path-finder">meta path finder<a class="headerlink" href="#term-meta-path-finder" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="#term-finder">finder</a> returned by a search of <a class="reference internal" href="library/sys.html#sys.meta_path" title="sys.meta_path"><code class="xref py py-data docutils literal notranslate">sys.meta_path</code></a>. Meta path finders are related to, but different from <a class="reference internal" href="#term-path-entry-finder">path entry finders</a>. See <a class="reference internal" href="library/importlib.html#importlib.abc.MetaPathFinder" title="importlib.abc.MetaPathFinder"><code class="xref py py-class docutils literal notranslate">importlib.abc.MetaPathFinder</code></a> for the methods that meta path finders implement. </dd> <dt id="term-metaclass">metaclass<a class="headerlink" href="#term-metaclass" title="Link to this term">¶</a></dt><dd>The class of a class. Class definitions create a class name, a class dictionary, and a list of base classes. The metaclass is responsible for taking those three arguments and creating the class. Most object oriented programming languages provide a default implementation. What makes Python special is that it is possible to create custom metaclasses. Most users never need this tool, but when the need arises, metaclasses can provide powerful, elegant solutions. They have been used for logging attribute access, adding thread-safety, tracking object creation, implementing singletons, and many other tasks. More information can be found in <a class="reference internal" href="reference/datamodel.html#metaclasses">Metaclasses</a>. </dd> <dt id="term-method">method<a class="headerlink" href="#term-method" title="Link to this term">¶</a></dt><dd>A function which is defined inside a class body. If called as an attribute of an instance of that class, the method will get the instance object as its first <a class="reference internal" href="#term-argument">argument</a> (which is usually called <code class="docutils literal notranslate">self</code>). See <a class="reference internal" href="#term-function">function</a> and <a class="reference internal" href="#term-nested-scope">nested scope</a>. </dd> <dt id="term-method-resolution-order">method resolution order<a class="headerlink" href="#term-method-resolution-order" title="Link to this term">¶</a></dt><dd>Method Resolution Order is the order in which base classes are searched for a member during lookup. See <a class="reference internal" href="howto/mro.html#python-2-3-mro">The Python 2.3 Method Resolution Order</a> for details of the algorithm used by the Python interpreter since the 2.3 release. </dd> <dt id="term-module">module<a class="headerlink" href="#term-module" title="Link to this term">¶</a></dt><dd>An object that serves as an organizational unit of Python code. Modules have a namespace containing arbitrary Python objects. Modules are loaded into Python by the process of <a class="reference internal" href="#term-importing">importing</a>. See also <a class="reference internal" href="#term-package">package</a>. </dd> <dt id="term-module-spec">module spec<a class="headerlink" href="#term-module-spec" title="Link to this term">¶</a></dt><dd>A namespace containing the import-related information used to load a module. An instance of <a class="reference internal" href="library/importlib.html#importlib.machinery.ModuleSpec" title="importlib.machinery.ModuleSpec"><code class="xref py py-class docutils literal notranslate">importlib.machinery.ModuleSpec</code></a>. See also <a class="reference internal" href="reference/import.html#module-specs">Module specs</a>. </dd> <dt id="term-MRO">MRO<a class="headerlink" href="#term-MRO" title="Link to this term">¶</a></dt><dd>See <a class="reference internal" href="#term-method-resolution-order">method resolution order</a>. </dd> <dt id="term-mutable">mutable<a class="headerlink" href="#term-mutable" title="Link to this term">¶</a></dt><dd>Mutable objects can change their value but keep their <a class="reference internal" href="library/functions.html#id" title="id"><code class="xref py py-func docutils literal notranslate">id()</code></a>. See also <a class="reference internal" href="#term-immutable">immutable</a>. </dd> <dt id="term-named-tuple">named tuple<a class="headerlink" href="#term-named-tuple" title="Link to this term">¶</a></dt><dd>The term “named tuple” applies to any type or class that inherits from tuple and whose indexable elements are also accessible using named attributes. The type or class may have other features as well. Several built-in types are named tuples, including the values returned by <a class="reference internal" href="library/time.html#time.localtime" title="time.localtime"><code class="xref py py-func docutils literal notranslate">time.localtime()</code></a> and <a class="reference internal" href="library/os.html#os.stat" title="os.stat"><code class="xref py py-func docutils literal notranslate">os.stat()</code></a>. Another example is <a class="reference internal" href="library/sys.html#sys.float_info" title="sys.float_info"><code class="xref py py-data docutils literal notranslate">sys.float_info</code></a>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> sys.float_info[1] # indexed access 1024 >>> sys.float_info.max_exp # named field access 1024 >>> isinstance(sys.float_info, tuple) # kind of tuple True </pre></div> </div> Some named tuples are built-in types (such as the above examples). Alternatively, a named tuple can be created from a regular class definition that inherits from <a class="reference internal" href="library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a> and that defines named fields. Such a class can be written by hand, or it can be created by inheriting <a class="reference internal" href="library/typing.html#typing.NamedTuple" title="typing.NamedTuple"><code class="xref py py-class docutils literal notranslate">typing.NamedTuple</code></a>, or with the factory function <a class="reference internal" href="library/collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-func docutils literal notranslate">collections.namedtuple()</code></a>. The latter techniques also add some extra methods that may not be found in hand-written or built-in named tuples. </dd> <dt id="term-namespace">namespace<a class="headerlink" href="#term-namespace" title="Link to this term">¶</a></dt><dd>The place where a variable is stored. Namespaces are implemented as dictionaries. There are the local, global and built-in namespaces as well as nested namespaces in objects (in methods). Namespaces support modularity by preventing naming conflicts. For instance, the functions <a class="reference internal" href="library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">builtins.open</code></a> and <a class="reference internal" href="library/os.html#os.open" title="os.open"><code class="xref py py-func docutils literal notranslate">os.open()</code></a> are distinguished by their namespaces. Namespaces also aid readability and maintainability by making it clear which module implements a function. For instance, writing <a class="reference internal" href="library/random.html#random.seed" title="random.seed"><code class="xref py py-func docutils literal notranslate">random.seed()</code></a> or <a class="reference internal" href="library/itertools.html#itertools.islice" title="itertools.islice"><code class="xref py py-func docutils literal notranslate">itertools.islice()</code></a> makes it clear that those functions are implemented by the <a class="reference internal" href="library/random.html#module-random" title="random: Generate pseudo-random numbers with various common distributions."><code class="xref py py-mod docutils literal notranslate">random</code></a> and <a class="reference internal" href="library/itertools.html#module-itertools" title="itertools: Functions creating iterators for efficient looping."><code class="xref py py-mod docutils literal notranslate">itertools</code></a> modules, respectively. </dd> <dt id="term-namespace-package">namespace package<a class="headerlink" href="#term-namespace-package" title="Link to this term">¶</a></dt><dd>A <a class="pep reference external" href="https://peps.python.org/pep-0420/">PEP 420</a> <a class="reference internal" href="#term-package">package</a> which serves only as a container for subpackages. Namespace packages may have no physical representation, and specifically are not like a <a class="reference internal" href="#term-regular-package">regular package</a> because they have no <code class="docutils literal notranslate">__init__.py</code> file. See also <a class="reference internal" href="#term-module">module</a>. </dd> <dt id="term-nested-scope">nested scope<a class="headerlink" href="#term-nested-scope" title="Link to this term">¶</a></dt><dd>The ability to refer to a variable in an enclosing definition. For instance, a function defined inside another function can refer to variables in the outer function. Note that nested scopes by default work only for reference and not for assignment. Local variables both read and write in the innermost scope. Likewise, global variables read and write to the global namespace. The <a class="reference internal" href="reference/simple_stmts.html#nonlocal"><code class="xref std std-keyword docutils literal notranslate">nonlocal</code></a> allows writing to outer scopes. </dd> <dt id="term-new-style-class">new-style class<a class="headerlink" href="#term-new-style-class" title="Link to this term">¶</a></dt><dd>Old name for the flavor of classes now used for all class objects. In earlier Python versions, only new-style classes could use Python’s newer, versatile features like <a class="reference internal" href="reference/datamodel.html#object.__slots__" title="object.__slots__"><code class="xref py py-attr docutils literal notranslate">__slots__</code></a>, descriptors, properties, <a class="reference internal" href="reference/datamodel.html#object.__getattribute__" title="object.__getattribute__"><code class="xref py py-meth docutils literal notranslate">__getattribute__()</code></a>, class methods, and static methods. </dd> <dt id="term-object">object<a class="headerlink" href="#term-object" title="Link to this term">¶</a></dt><dd>Any data with state (attributes or value) and defined behavior (methods). Also the ultimate base class of any <a class="reference internal" href="#term-new-style-class">new-style class</a>. </dd> <dt id="term-optimized-scope">optimized scope<a class="headerlink" href="#term-optimized-scope" title="Link to this term">¶</a></dt><dd>A scope where target local variable names are reliably known to the compiler when the code is compiled, allowing optimization of read and write access to these names. The local namespaces for functions, generators, coroutines, comprehensions, and generator expressions are optimized in this fashion. Note: most interpreter optimizations are applied to all scopes, only those relying on a known set of local and nonlocal variable names are restricted to optimized scopes. </dd> <dt id="term-package">package<a class="headerlink" href="#term-package" title="Link to this term">¶</a></dt><dd>A Python <a class="reference internal" href="#term-module">module</a> which can contain submodules or recursively, subpackages. Technically, a package is a Python module with a <code class="docutils literal notranslate">__path__</code> attribute. See also <a class="reference internal" href="#term-regular-package">regular package</a> and <a class="reference internal" href="#term-namespace-package">namespace package</a>. </dd> <dt id="term-parameter">parameter<a class="headerlink" href="#term-parameter" title="Link to this term">¶</a></dt><dd>A named entity in a <a class="reference internal" href="#term-function">function</a> (or method) definition that specifies an <a class="reference internal" href="#term-argument">argument</a> (or in some cases, arguments) that the function can accept. There are five kinds of parameter: <ul> <li>positional-or-keyword: specifies an argument that can be passed either <a class="reference internal" href="#term-argument">positionally</a> or as a <a class="reference internal" href="#term-argument">keyword argument</a>. This is the default kind of parameter, for example foo and bar in the following: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def func(foo, bar=None): ... </pre></div> </div> </li> </ul> <ul id="positional-only-parameter"> <li>positional-only: specifies an argument that can be supplied only by position. Positional-only parameters can be defined by including a <code class="docutils literal notranslate">/</code> character in the parameter list of the function definition after them, for example posonly1 and posonly2 in the following: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def func(posonly1, posonly2, /, positional_or_keyword): ... </pre></div> </div> </li> </ul> <ul id="keyword-only-parameter"> <li>keyword-only: specifies an argument that can be supplied only by keyword. Keyword-only parameters can be defined by including a single var-positional parameter or bare <code class="docutils literal notranslate">*</code> in the parameter list of the function definition before them, for example kw_only1 and kw_only2 in the following: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def func(arg, *, kw_only1, kw_only2): ... </pre></div> </div> </li> <li>var-positional: specifies that an arbitrary sequence of positional arguments can be provided (in addition to any positional arguments already accepted by other parameters). Such a parameter can be defined by prepending the parameter name with <code class="docutils literal notranslate">*</code>, for example args in the following: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def func(*args, **kwargs): ... </pre></div> </div> </li> <li>var-keyword: specifies that arbitrarily many keyword arguments can be provided (in addition to any keyword arguments already accepted by other parameters). Such a parameter can be defined by prepending the parameter name with <code class="docutils literal notranslate">**</code>, for example kwargs in the example above.</li> </ul> Parameters can specify both optional and required arguments, as well as default values for some optional arguments. See also the <a class="reference internal" href="#term-argument">argument</a> glossary entry, the FAQ question on <a class="reference internal" href="faq/programming.html#faq-argument-vs-parameter">the difference between arguments and parameters</a>, the <a class="reference internal" href="library/inspect.html#inspect.Parameter" title="inspect.Parameter"><code class="xref py py-class docutils literal notranslate">inspect.Parameter</code></a> class, the <a class="reference internal" href="reference/compound_stmts.html#function">Function definitions</a> section, and <a class="pep reference external" href="https://peps.python.org/pep-0362/">PEP 362</a>. </dd> <dt id="term-path-entry">path entry<a class="headerlink" href="#term-path-entry" title="Link to this term">¶</a></dt><dd>A single location on the <a class="reference internal" href="#term-import-path">import path</a> which the <a class="reference internal" href="#term-path-based-finder">path based finder</a> consults to find modules for importing. </dd> <dt id="term-path-entry-finder">path entry finder<a class="headerlink" href="#term-path-entry-finder" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="#term-finder">finder</a> returned by a callable on <a class="reference internal" href="library/sys.html#sys.path_hooks" title="sys.path_hooks"><code class="xref py py-data docutils literal notranslate">sys.path_hooks</code></a> (i.e. a <a class="reference internal" href="#term-path-entry-hook">path entry hook</a>) which knows how to locate modules given a <a class="reference internal" href="#term-path-entry">path entry</a>. See <a class="reference internal" href="library/importlib.html#importlib.abc.PathEntryFinder" title="importlib.abc.PathEntryFinder"><code class="xref py py-class docutils literal notranslate">importlib.abc.PathEntryFinder</code></a> for the methods that path entry finders implement. </dd> <dt id="term-path-entry-hook">path entry hook<a class="headerlink" href="#term-path-entry-hook" title="Link to this term">¶</a></dt><dd>A callable on the <a class="reference internal" href="library/sys.html#sys.path_hooks" title="sys.path_hooks"><code class="xref py py-data docutils literal notranslate">sys.path_hooks</code></a> list which returns a <a class="reference internal" href="#term-path-entry-finder">path entry finder</a> if it knows how to find modules on a specific <a class="reference internal" href="#term-path-entry">path entry</a>. </dd> <dt id="term-path-based-finder">path based finder<a class="headerlink" href="#term-path-based-finder" title="Link to this term">¶</a></dt><dd>One of the default <a class="reference internal" href="#term-meta-path-finder">meta path finders</a> which searches an <a class="reference internal" href="#term-import-path">import path</a> for modules. </dd> <dt id="term-path-like-object">path-like object<a class="headerlink" href="#term-path-like-object" title="Link to this term">¶</a></dt><dd>An object representing a file system path. A path-like object is either a <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> or <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> object representing a path, or an object implementing the <a class="reference internal" href="library/os.html#os.PathLike" title="os.PathLike"><code class="xref py py-class docutils literal notranslate">os.PathLike</code></a> protocol. An object that supports the <a class="reference internal" href="library/os.html#os.PathLike" title="os.PathLike"><code class="xref py py-class docutils literal notranslate">os.PathLike</code></a> protocol can be converted to a <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> or <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> file system path by calling the <a class="reference internal" href="library/os.html#os.fspath" title="os.fspath"><code class="xref py py-func docutils literal notranslate">os.fspath()</code></a> function; <a class="reference internal" href="library/os.html#os.fsdecode" title="os.fsdecode"><code class="xref py py-func docutils literal notranslate">os.fsdecode()</code></a> and <a class="reference internal" href="library/os.html#os.fsencode" title="os.fsencode"><code class="xref py py-func docutils literal notranslate">os.fsencode()</code></a> can be used to guarantee a <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> or <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> result instead, respectively. Introduced by <a class="pep reference external" href="https://peps.python.org/pep-0519/">PEP 519</a>. </dd> <dt id="term-PEP">PEP<a class="headerlink" href="#term-PEP" title="Link to this term">¶</a></dt><dd>Python Enhancement Proposal. A PEP is a design document providing information to the Python community, or describing a new feature for Python or its processes or environment. PEPs should provide a concise technical specification and a rationale for proposed features. PEPs are intended to be the primary mechanisms for proposing major new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python. The PEP author is responsible for building consensus within the community and documenting dissenting opinions. See <a class="pep reference external" href="https://peps.python.org/pep-0001/">PEP 1</a>. </dd> <dt id="term-portion">portion<a class="headerlink" href="#term-portion" title="Link to this term">¶</a></dt><dd>A set of files in a single directory (possibly stored in a zip file) that contribute to a namespace package, as defined in <a class="pep reference external" href="https://peps.python.org/pep-0420/">PEP 420</a>. </dd> <dt id="term-positional-argument">positional argument<a class="headerlink" href="#term-positional-argument" title="Link to this term">¶</a></dt><dd>See <a class="reference internal" href="#term-argument">argument</a>. </dd> <dt id="term-provisional-API">provisional API<a class="headerlink" href="#term-provisional-API" title="Link to this term">¶</a></dt><dd>A provisional API is one which has been deliberately excluded from the standard library’s backwards compatibility guarantees. While major changes to such interfaces are not expected, as long as they are marked provisional, backwards incompatible changes (up to and including removal of the interface) may occur if deemed necessary by core developers. Such changes will not be made gratuitously – they will occur only if serious fundamental flaws are uncovered that were missed prior to the inclusion of the API. Even for provisional APIs, backwards incompatible changes are seen as a “solution of last resort” - every attempt will still be made to find a backwards compatible resolution to any identified problems. This process allows the standard library to continue to evolve over time, without locking in problematic design errors for extended periods of time. See <a class="pep reference external" href="https://peps.python.org/pep-0411/">PEP 411</a> for more details. </dd> <dt id="term-provisional-package">provisional package<a class="headerlink" href="#term-provisional-package" title="Link to this term">¶</a></dt><dd>See <a class="reference internal" href="#term-provisional-API">provisional API</a>. </dd> <dt id="term-Python-3000">Python 3000<a class="headerlink" href="#term-Python-3000" title="Link to this term">¶</a></dt><dd>Nickname for the Python 3.x release line (coined long ago when the release of version 3 was something in the distant future.) This is also abbreviated “Py3k”. </dd> <dt id="term-Pythonic">Pythonic<a class="headerlink" href="#term-Pythonic" title="Link to this term">¶</a></dt><dd>An idea or piece of code which closely follows the most common idioms of the Python language, rather than implementing code using concepts common to other languages. For example, a common idiom in Python is to loop over all elements of an iterable using a <a class="reference internal" href="reference/compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate">for</code></a> statement. Many other languages don’t have this type of construct, so people unfamiliar with Python sometimes use a numerical counter instead: <div class="highlight-python3 notranslate"><div class="highlight"><pre>for i in range(len(food)): print(food[i]) </pre></div> </div> As opposed to the cleaner, Pythonic method: <div class="highlight-python3 notranslate"><div class="highlight"><pre>for piece in food: print(piece) </pre></div> </div> </dd> <dt id="term-qualified-name">qualified name<a class="headerlink" href="#term-qualified-name" title="Link to this term">¶</a></dt><dd>A dotted name showing the “path” from a module’s global scope to a class, function or method defined in that module, as defined in <a class="pep reference external" href="https://peps.python.org/pep-3155/">PEP 3155</a>. For top-level functions and classes, the qualified name is the same as the object’s name: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class C: ... class D: ... def meth(self): ... pass ... >>> C.__qualname__ 'C' >>> C.D.__qualname__ 'C.D' >>> C.D.meth.__qualname__ 'C.D.meth' </pre></div> </div> When used to refer to modules, the fully qualified name means the entire dotted path to the module, including any parent packages, e.g. <code class="docutils literal notranslate">email.mime.text</code>: <div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> import email.mime.text >>> email.mime.text.__name__ 'email.mime.text' </pre></div> </div> </dd> <dt id="term-reference-count">reference count<a class="headerlink" href="#term-reference-count" title="Link to this term">¶</a></dt><dd>The number of references to an object. When the reference count of an object drops to zero, it is deallocated. Some objects are <a class="reference internal" href="#term-immortal">immortal</a> and have reference counts that are never modified, and therefore the objects are never deallocated. Reference counting is generally not visible to Python code, but it is a key element of the <a class="reference internal" href="#term-CPython">CPython</a> implementation. Programmers can call the <a class="reference internal" href="library/sys.html#sys.getrefcount" title="sys.getrefcount"><code class="xref py py-func docutils literal notranslate">sys.getrefcount()</code></a> function to return the reference count for a particular object. </dd> <dt id="term-regular-package">regular package<a class="headerlink" href="#term-regular-package" title="Link to this term">¶</a></dt><dd>A traditional <a class="reference internal" href="#term-package">package</a>, such as a directory containing an <code class="docutils literal notranslate">__init__.py</code> file. See also <a class="reference internal" href="#term-namespace-package">namespace package</a>. </dd> <dt id="term-REPL">REPL<a class="headerlink" href="#term-REPL" title="Link to this term">¶</a></dt><dd>An acronym for the “read–eval–print loop”, another name for the <a class="reference internal" href="#term-interactive">interactive</a> interpreter shell. </dd> <dt id="term-__slots__">__slots__<a class="headerlink" href="#term-__slots__" title="Link to this term">¶</a></dt><dd>A declaration inside a class that saves memory by pre-declaring space for instance attributes and eliminating instance dictionaries. Though popular, the technique is somewhat tricky to get right and is best reserved for rare cases where there are large numbers of instances in a memory-critical application. </dd> <dt id="term-sequence">sequence<a class="headerlink" href="#term-sequence" title="Link to this term">¶</a></dt><dd>An <a class="reference internal" href="#term-iterable">iterable</a> which supports efficient element access using integer indices via the <a class="reference internal" href="reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> special method and defines a <a class="reference internal" href="reference/datamodel.html#object.__len__" title="object.__len__"><code class="xref py py-meth docutils literal notranslate">__len__()</code></a> method that returns the length of the sequence. Some built-in sequence types are <a class="reference internal" href="library/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate">list</code></a>, <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>, <a class="reference internal" href="library/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate">tuple</code></a>, and <a class="reference internal" href="library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a>. Note that <a class="reference internal" href="library/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate">dict</code></a> also supports <a class="reference internal" href="reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> and <code class="xref py py-meth docutils literal notranslate">__len__()</code>, but is considered a mapping rather than a sequence because the lookups use arbitrary <a class="reference internal" href="#term-hashable">hashable</a> keys rather than integers. The <a class="reference internal" href="library/collections.abc.html#collections.abc.Sequence" title="collections.abc.Sequence"><code class="xref py py-class docutils literal notranslate">collections.abc.Sequence</code></a> abstract base class defines a much richer interface that goes beyond just <a class="reference internal" href="reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a> and <a class="reference internal" href="reference/datamodel.html#object.__len__" title="object.__len__"><code class="xref py py-meth docutils literal notranslate">__len__()</code></a>, adding <code class="xref py py-meth docutils literal notranslate">count()</code>, <code class="xref py py-meth docutils literal notranslate">index()</code>, <a class="reference internal" href="reference/datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate">__contains__()</code></a>, and <a class="reference internal" href="reference/datamodel.html#object.__reversed__" title="object.__reversed__"><code class="xref py py-meth docutils literal notranslate">__reversed__()</code></a>. Types that implement this expanded interface can be registered explicitly using <a class="reference internal" href="library/abc.html#abc.ABCMeta.register" title="abc.ABCMeta.register"><code class="xref py py-func docutils literal notranslate">register()</code></a>. For more documentation on sequence methods generally, see <a class="reference internal" href="library/stdtypes.html#typesseq-common">Common Sequence Operations</a>. </dd> <dt id="term-set-comprehension">set comprehension<a class="headerlink" href="#term-set-comprehension" title="Link to this term">¶</a></dt><dd>A compact way to process all or part of the elements in an iterable and return a set with the results. <code class="docutils literal notranslate">results = {c for c in 'abracadabra' if c not in 'abc'}</code> generates the set of strings <code class="docutils literal notranslate">{'r', 'd'}</code>. See <a class="reference internal" href="reference/expressions.html#comprehensions">Displays for lists, sets and dictionaries</a>. </dd> <dt id="term-single-dispatch">single dispatch<a class="headerlink" href="#term-single-dispatch" title="Link to this term">¶</a></dt><dd>A form of <a class="reference internal" href="#term-generic-function">generic function</a> dispatch where the implementation is chosen based on the type of a single argument. </dd> <dt id="term-slice">slice<a class="headerlink" href="#term-slice" title="Link to this term">¶</a></dt><dd>An object usually containing a portion of a <a class="reference internal" href="#term-sequence">sequence</a>. A slice is created using the subscript notation, <code class="docutils literal notranslate">[]</code> with colons between numbers when several are given, such as in <code class="docutils literal notranslate">variable_name[1:3:5]</code>. The bracket (subscript) notation uses <a class="reference internal" href="library/functions.html#slice" title="slice"><code class="xref py py-class docutils literal notranslate">slice</code></a> objects internally. </dd> <dt id="term-soft-deprecated">soft deprecated<a class="headerlink" href="#term-soft-deprecated" title="Link to this term">¶</a></dt><dd>A soft deprecated API should not be used in new code, but it is safe for already existing code to use it. The API remains documented and tested, but will not be enhanced further. Soft deprecation, unlike normal deprecation, does not plan on removing the API and will not emit warnings. See <a class="reference external" href="https://peps.python.org/pep-0387/#soft-deprecation">PEP 387: Soft Deprecation</a>. </dd> <dt id="term-special-method">special method<a class="headerlink" href="#term-special-method" title="Link to this term">¶</a></dt><dd>A method that is called implicitly by Python to execute a certain operation on a type, such as addition. Such methods have names starting and ending with double underscores. Special methods are documented in <a class="reference internal" href="reference/datamodel.html#specialnames">Special method names</a>. </dd> <dt id="term-statement">statement<a class="headerlink" href="#term-statement" title="Link to this term">¶</a></dt><dd>A statement is part of a suite (a “block” of code). A statement is either an <a class="reference internal" href="#term-expression">expression</a> or one of several constructs with a keyword, such as <a class="reference internal" href="reference/compound_stmts.html#if"><code class="xref std std-keyword docutils literal notranslate">if</code></a>, <a class="reference internal" href="reference/compound_stmts.html#while"><code class="xref std std-keyword docutils literal notranslate">while</code></a> or <a class="reference internal" href="reference/compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate">for</code></a>. </dd> <dt id="term-static-type-checker">static type checker<a class="headerlink" href="#term-static-type-checker" title="Link to this term">¶</a></dt><dd>An external tool that reads Python code and analyzes it, looking for issues such as incorrect types. See also <a class="reference internal" href="#term-type-hint">type hints</a> and the <a class="reference internal" href="library/typing.html#module-typing" title="typing: Support for type hints (see :pep:`484`)."><code class="xref py py-mod docutils literal notranslate">typing</code></a> module. </dd> <dt id="term-strong-reference">strong reference<a class="headerlink" href="#term-strong-reference" title="Link to this term">¶</a></dt><dd>In Python’s C API, a strong reference is a reference to an object which is owned by the code holding the reference. The strong reference is taken by calling <a class="reference internal" href="c-api/refcounting.html#c.Py_INCREF" title="Py_INCREF"><code class="xref c c-func docutils literal notranslate">Py_INCREF()</code></a> when the reference is created and released with <a class="reference internal" href="c-api/refcounting.html#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a> when the reference is deleted. The <a class="reference internal" href="c-api/refcounting.html#c.Py_NewRef" title="Py_NewRef"><code class="xref c c-func docutils literal notranslate">Py_NewRef()</code></a> function can be used to create a strong reference to an object. Usually, the <a class="reference internal" href="c-api/refcounting.html#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate">Py_DECREF()</code></a> function must be called on the strong reference before exiting the scope of the strong reference, to avoid leaking one reference. See also <a class="reference internal" href="#term-borrowed-reference">borrowed reference</a>. </dd> <dt id="term-text-encoding">text encoding<a class="headerlink" href="#term-text-encoding" title="Link to this term">¶</a></dt><dd>A string in Python is a sequence of Unicode code points (in range <code class="docutils literal notranslate">U+0000</code>–<code class="docutils literal notranslate">U+10FFFF</code>). To store or transfer a string, it needs to be serialized as a sequence of bytes. Serializing a string into a sequence of bytes is known as “encoding”, and recreating the string from the sequence of bytes is known as “decoding”. There are a variety of different text serialization <a class="reference internal" href="library/codecs.html#standard-encodings">codecs</a>, which are collectively referred to as “text encodings”. </dd> <dt id="term-text-file">text file<a class="headerlink" href="#term-text-file" title="Link to this term">¶</a></dt><dd>A <a class="reference internal" href="#term-file-object">file object</a> able to read and write <a class="reference internal" href="library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> objects. Often, a text file actually accesses a byte-oriented datastream and handles the <a class="reference internal" href="#term-text-encoding">text encoding</a> automatically. Examples of text files are files opened in text mode (<code class="docutils literal notranslate">'r'</code> or <code class="docutils literal notranslate">'w'</code>), <a class="reference internal" href="library/sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate">sys.stdin</code></a>, <a class="reference internal" href="library/sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate">sys.stdout</code></a>, and instances of <a class="reference internal" href="library/io.html#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate">io.StringIO</code></a>. See also <a class="reference internal" href="#term-binary-file">binary file</a> for a file object able to read and write <a class="reference internal" href="#term-bytes-like-object">bytes-like objects</a>. </dd> <dt id="term-triple-quoted-string">triple-quoted string<a class="headerlink" href="#term-triple-quoted-string" title="Link to this term">¶</a></dt><dd>A string which is bound by three instances of either a quotation mark (”) or an apostrophe (‘). While they don’t provide any functionality not available with single-quoted strings, they are useful for a number of reasons. They allow you to include unescaped single and double quotes within a string and they can span multiple lines without the use of the continuation character, making them especially useful when writing docstrings. </dd> <dt id="term-type">type<a class="headerlink" href="#term-type" title="Link to this term">¶</a></dt><dd>The type of a Python object determines what kind of object it is; every object has a type. An object’s type is accessible as its <a class="reference internal" href="reference/datamodel.html#object.__class__" title="object.__class__"><code class="xref py py-attr docutils literal notranslate">__class__</code></a> attribute or can be retrieved with <code class="docutils literal notranslate">type(obj)</code>. </dd> <dt id="term-type-alias">type alias<a class="headerlink" href="#term-type-alias" title="Link to this term">¶</a></dt><dd>A synonym for a type, created by assigning the type to an identifier. Type aliases are useful for simplifying <a class="reference internal" href="#term-type-hint">type hints</a>. For example: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def remove_gray_shades( colors: list[tuple[int, int, int]]) -> list[tuple[int, int, int]]: pass </pre></div> </div> could be made more readable like this: <div class="highlight-python3 notranslate"><div class="highlight"><pre>Color = tuple[int, int, int] def remove_gray_shades(colors: list[Color]) -> list[Color]: pass </pre></div> </div> See <a class="reference internal" href="library/typing.html#module-typing" title="typing: Support for type hints (see :pep:`484`)."><code class="xref py py-mod docutils literal notranslate">typing</code></a> and <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a>, which describe this functionality. </dd> <dt id="term-type-hint">type hint<a class="headerlink" href="#term-type-hint" title="Link to this term">¶</a></dt><dd>An <a class="reference internal" href="#term-annotation">annotation</a> that specifies the expected type for a variable, a class attribute, or a function parameter or return value. Type hints are optional and are not enforced by Python but they are useful to <a class="reference internal" href="#term-static-type-checker">static type checkers</a>. They can also aid IDEs with code completion and refactoring. Type hints of global variables, class attributes, and functions, but not local variables, can be accessed using <a class="reference internal" href="library/typing.html#typing.get_type_hints" title="typing.get_type_hints"><code class="xref py py-func docutils literal notranslate">typing.get_type_hints()</code></a>. See <a class="reference internal" href="library/typing.html#module-typing" title="typing: Support for type hints (see :pep:`484`)."><code class="xref py py-mod docutils literal notranslate">typing</code></a> and <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a>, which describe this functionality. </dd> <dt id="term-universal-newlines">universal newlines<a class="headerlink" href="#term-universal-newlines" title="Link to this term">¶</a></dt><dd>A manner of interpreting text streams in which all of the following are recognized as ending a line: the Unix end-of-line convention <code class="docutils literal notranslate">'\n'</code>, the Windows convention <code class="docutils literal notranslate">'\r\n'</code>, and the old Macintosh convention <code class="docutils literal notranslate">'\r'</code>. See <a class="pep reference external" href="https://peps.python.org/pep-0278/">PEP 278</a> and <a class="pep reference external" href="https://peps.python.org/pep-3116/">PEP 3116</a>, as well as <a class="reference internal" href="library/stdtypes.html#bytes.splitlines" title="bytes.splitlines"><code class="xref py py-func docutils literal notranslate">bytes.splitlines()</code></a> for an additional use. </dd> <dt id="term-variable-annotation">variable annotation<a class="headerlink" href="#term-variable-annotation" title="Link to this term">¶</a></dt><dd>An <a class="reference internal" href="#term-annotation">annotation</a> of a variable or a class attribute. When annotating a variable or a class attribute, assignment is optional: <div class="highlight-python3 notranslate"><div class="highlight"><pre>class C: field: 'annotation' </pre></div> </div> Variable annotations are usually used for <a class="reference internal" href="#term-type-hint">type hints</a>: for example this variable is expected to take <a class="reference internal" href="library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a> values: <div class="highlight-python3 notranslate"><div class="highlight"><pre>count: int = 0 </pre></div> </div> Variable annotation syntax is explained in section <a class="reference internal" href="reference/simple_stmts.html#annassign">Annotated assignment statements</a>. See <a class="reference internal" href="#term-function-annotation">function annotation</a>, <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-0526/">PEP 526</a>, which describe this functionality. Also see <a class="reference internal" href="howto/annotations.html#annotations-howto">Annotations Best Practices</a> for best practices on working with annotations. </dd> <dt id="term-virtual-environment">virtual environment<a class="headerlink" href="#term-virtual-environment" title="Link to this term">¶</a></dt><dd>A cooperatively isolated runtime environment that allows Python users and applications to install and upgrade Python distribution packages without interfering with the behaviour of other Python applications running on the same system. See also <a class="reference internal" href="library/venv.html#module-venv" title="venv: Creation of virtual environments."><code class="xref py py-mod docutils literal notranslate">venv</code></a>. </dd> <dt id="term-virtual-machine">virtual machine<a class="headerlink" href="#term-virtual-machine" title="Link to this term">¶</a></dt><dd>A computer defined entirely in software. Python’s virtual machine executes the <a class="reference internal" href="#term-bytecode">bytecode</a> emitted by the bytecode compiler. </dd> <dt id="term-Zen-of-Python">Zen of Python<a class="headerlink" href="#term-Zen-of-Python" title="Link to this term">¶</a></dt><dd>Listing of Python design principles and philosophies that are helpful in understanding and using the language. The listing can be found by typing “<code class="docutils literal notranslate">import this</code>” at the interactive prompt. </dd> </dl> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h4>Previous topic</h4> <a href="deprecations/index.html" title="previous chapter">Deprecations</a> </div> <div> <h4>Next topic</h4> <a href="about.html" title="next chapter">About these documents</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/glossary.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" >index</a></li> <li class="right" > <a href="py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="about.html" title="About these documents" >next</a> |</li> <li class="right" > <a href="deprecations/index.html" title="Deprecations" >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-this"><a href="">Glossary</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="footer"> © <a href="copyright.html"> Copyright </a> 2001-2024, Python Software Foundation. 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