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<li><a class="reference internal" href="#">6. Expressions</a><ul>
<li><a class="reference internal" href="#arithmetic-conversions">6.1. Arithmetic conversions</a></li>
<li><a class="reference internal" href="#atoms">6.2. Atoms</a><ul>
<li><a class="reference internal" href="#built-in-constants">6.2.1. Built-in constants</a></li>
<li><a class="reference internal" href="#atom-identifiers">6.2.2. Identifiers (Names)</a><ul>
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<li><a class="reference internal" href="#set-displays">6.2.7. Set displays</a></li>
<li><a class="reference internal" href="#dictionary-displays">6.2.8. Dictionary displays</a></li>
<li><a class="reference internal" href="#generator-expressions">6.2.9. Generator expressions</a></li>
<li><a class="reference internal" href="#yield-expressions">6.2.10. Yield expressions</a><ul>
<li><a class="reference internal" href="#generator-iterator-methods">6.2.10.1. Generator-iterator methods</a></li>
<li><a class="reference internal" href="#examples">6.2.10.2. Examples</a></li>
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<li><a class="reference internal" href="#expression-lists">6.15. Expression lists</a></li>
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<section id="expressions">
<span id="id1"></span><h1><span class="section-number">6. </span>Expressions<a class="headerlink" href="#expressions" title="Link to this heading">¶</a></h1>
<p id="index-0">This chapter explains the meaning of the elements of expressions in Python.</p>
<p><strong>Syntax Notes:</strong> In this and the following chapters,
<a class="reference internal" href="introduction.html#notation"><span class="std std-ref">grammar notation</span></a> will be used to describe syntax,
not lexical analysis.</p>
<p>When (one alternative of) a syntax rule has the form:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-name">name</strong>: othername
</pre>
<p>and no semantics are given, the semantics of this form of <code class="docutils literal notranslate"><span class="pre">name</span></code> are the same
as for <code class="docutils literal notranslate"><span class="pre">othername</span></code>.</p>
<section id="arithmetic-conversions">
<span id="conversions"></span><h2><span class="section-number">6.1. </span>Arithmetic conversions<a class="headerlink" href="#arithmetic-conversions" title="Link to this heading">¶</a></h2>
<p id="index-1">When a description of an arithmetic operator below uses the phrase "the numeric
arguments are converted to a common real type", this means that the operator
implementation for built-in numeric types works as described in the
<a class="reference internal" href="../library/stdtypes.html#stdtypes-mixed-arithmetic"><span class="std std-ref">Numeric Types</span></a> section of the standard
library documentation.</p>
<p>Some additional rules apply for certain operators and non-numeric operands
(for example, a string as a left argument to the <code class="docutils literal notranslate"><span class="pre">%</span></code> operator).
Extensions must define their own conversion behavior.</p>
</section>
<section id="atoms">
<span id="id2"></span><h2><span class="section-number">6.2. </span>Atoms<a class="headerlink" href="#atoms" title="Link to this heading">¶</a></h2>
<p id="index-2">Atoms are the most basic elements of expressions.
The simplest atoms are <a class="reference internal" href="lexical_analysis.html#identifiers"><span class="std std-ref">names</span></a> or literals.
Forms enclosed in parentheses, brackets or braces are also categorized
syntactically as atoms.</p>
<p>Formally, the syntax for atoms is:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-atom">atom</strong>:
| <span class="sx">'True'</span>
| <span class="sx">'False'</span>
| <span class="sx">'None'</span>
| <span class="sx">'...'</span>
| <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-identifier"><code class="xref docutils literal notranslate"><span class="pre">identifier</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-literal"><code class="xref docutils literal notranslate"><span class="pre">literal</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-enclosure"><code class="xref docutils literal notranslate"><span class="pre">enclosure</span></code></a>
<strong id="grammar-token-python-grammar-enclosure">enclosure</strong>:
| <a class="reference internal" href="#grammar-token-python-grammar-parenth_form"><code class="xref docutils literal notranslate"><span class="pre">parenth_form</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-list_display"><code class="xref docutils literal notranslate"><span class="pre">list_display</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-dict_display"><code class="xref docutils literal notranslate"><span class="pre">dict_display</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-set_display"><code class="xref docutils literal notranslate"><span class="pre">set_display</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-generator_expression"><code class="xref docutils literal notranslate"><span class="pre">generator_expression</span></code></a>
| <a class="reference internal" href="#grammar-token-python-grammar-yield_atom"><code class="xref docutils literal notranslate"><span class="pre">yield_atom</span></code></a>
</pre>
<section id="built-in-constants">
<span id="atom-singletons"></span><h3><span class="section-number">6.2.1. </span>Built-in constants<a class="headerlink" href="#built-in-constants" title="Link to this heading">¶</a></h3>
<p>The keywords <code class="docutils literal notranslate"><span class="pre">True</span></code>, <code class="docutils literal notranslate"><span class="pre">False</span></code>, and <code class="docutils literal notranslate"><span class="pre">None</span></code> name
<a class="reference internal" href="../library/constants.html#built-in-consts"><span class="std std-ref">built-in constants</span></a>.
The token <code class="docutils literal notranslate"><span class="pre">...</span></code> names the <a class="reference internal" href="../library/constants.html#Ellipsis" title="Ellipsis"><code class="xref py py-data docutils literal notranslate"><span class="pre">Ellipsis</span></code></a> constant.</p>
<p>Evaluation of these atoms yields the corresponding value.</p>
<div class="admonition note">
<p class="admonition-title">توجه</p>
<p>Several more built-in constants are available as global variables,
but only the ones mentioned here are <a class="reference internal" href="lexical_analysis.html#keywords"><span class="std std-ref">keywords</span></a>.
In particular, these names cannot be reassigned or used as attributes:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kc">False</span> <span class="o">=</span> <span class="mi">123</span>
File <span class="nb">"<input>"</span>, line <span class="m">1</span>
<span class="gr"> False = 123</span>
<span class="gr"> ^^^^^</span>
<span class="gr">SyntaxError</span>: <span class="n">cannot assign to False</span>
</pre></div>
</div>
</div>
</section>
<section id="atom-identifiers">
<span id="identifiers-names"></span><h3><span class="section-number">6.2.2. </span>Identifiers (Names)<a class="headerlink" href="#atom-identifiers" title="Link to this heading">¶</a></h3>
<p id="index-3">An identifier occurring as an atom is a name. See section <a class="reference internal" href="lexical_analysis.html#identifiers"><span class="std std-ref">Names (identifiers and keywords)</span></a>
for lexical definition and section <a class="reference internal" href="executionmodel.html#naming"><span class="std std-ref">Naming and binding</span></a> for documentation of naming and
binding.</p>
<p id="index-4">When the name is bound to an object, evaluation of the atom yields that object.
When a name is not bound, an attempt to evaluate it raises a <a class="reference internal" href="../library/exceptions.html#NameError" title="NameError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NameError</span></code></a>
exception.</p>
<section id="index-5">
<span id="private-name-mangling"></span><span id="id3"></span><h4><span class="section-number">6.2.2.1. </span>Private name mangling<a class="headerlink" href="#index-5" title="Link to this heading">¶</a></h4>
<p>When an identifier that textually occurs in a class definition begins with two
or more underscore characters and does not end in two or more underscores, it
is considered a <em class="dfn">private name</em> of that class.</p>
<div class="admonition seealso">
<p class="admonition-title">همچنین ملاحظه نمائید</p>
<p>The <a class="reference internal" href="compound_stmts.html#class"><span class="std std-ref">class specifications</span></a>.</p>
</div>
<p>More precisely, private names are transformed to a longer form before code is
generated for them. If the transformed name is longer than 255 characters,
implementation-defined truncation may happen.</p>
<p>The transformation is independent of the syntactical context in which the
identifier is used but only the following private identifiers are mangled:</p>
<ul>
<li><p>Any name used as the name of a variable that is assigned or read or any
name of an attribute being accessed.</p>
<p>The <a class="reference internal" href="../library/stdtypes.html#definition.__name__" title="definition.__name__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__name__</span></code></a> attribute of nested functions, classes, and
type aliases is however not mangled.</p>
</li>
<li><p>The name of imported modules, e.g., <code class="docutils literal notranslate"><span class="pre">__spam</span></code> in <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">__spam</span></code>.
If the module is part of a package (i.e., its name contains a dot),
the name is <em>not</em> mangled, e.g., the <code class="docutils literal notranslate"><span class="pre">__foo</span></code> in <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">__foo.bar</span></code>
is not mangled.</p></li>
<li><p>The name of an imported member, e.g., <code class="docutils literal notranslate"><span class="pre">__f</span></code> in <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">spam</span> <span class="pre">import</span> <span class="pre">__f</span></code>.</p></li>
</ul>
<p>The transformation rule is defined as follows:</p>
<ul class="simple">
<li><p>The class name, with leading underscores removed and a single leading
underscore inserted, is inserted in front of the identifier, e.g., the
identifier <code class="docutils literal notranslate"><span class="pre">__spam</span></code> occurring in a class named <code class="docutils literal notranslate"><span class="pre">Foo</span></code>, <code class="docutils literal notranslate"><span class="pre">_Foo</span></code> or
<code class="docutils literal notranslate"><span class="pre">__Foo</span></code> is transformed to <code class="docutils literal notranslate"><span class="pre">_Foo__spam</span></code>.</p></li>
<li><p>If the class name consists only of underscores, the transformation is the
identity, e.g., the identifier <code class="docutils literal notranslate"><span class="pre">__spam</span></code> occurring in a class named <code class="docutils literal notranslate"><span class="pre">_</span></code>
or <code class="docutils literal notranslate"><span class="pre">__</span></code> is left as is.</p></li>
</ul>
</section>
</section>
<section id="literals">
<span id="atom-literals"></span><h3><span class="section-number">6.2.3. </span>Literals<a class="headerlink" href="#literals" title="Link to this heading">¶</a></h3>
<p id="index-6">A <em class="dfn">literal</em> is a textual representation of a value.
Python supports numeric, string and bytes literals.
<a class="reference internal" href="lexical_analysis.html#f-strings"><span class="std std-ref">Format strings</span></a> and <a class="reference internal" href="lexical_analysis.html#t-strings"><span class="std std-ref">template strings</span></a>
are treated as string literals.</p>
<p>Numeric literals consist of a single <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-NUMBER"><code class="xref std std-token docutils literal notranslate"><span class="pre">NUMBER</span></code></a>
token, which names an integer, floating-point number, or an imaginary number.
See the <a class="reference internal" href="lexical_analysis.html#numbers"><span class="std std-ref">Numeric literals</span></a> section in Lexical analysis documentation for details.</p>
<p>String and bytes literals may consist of several tokens.
See section <a class="reference internal" href="#string-concatenation"><span class="std std-ref">String literal concatenation</span></a> for details.</p>
<p>Note that negative and complex numbers, like <code class="docutils literal notranslate"><span class="pre">-3</span></code> or <code class="docutils literal notranslate"><span class="pre">3+4.2j</span></code>,
are syntactically not literals, but <a class="reference internal" href="#unary"><span class="std std-ref">unary</span></a> or
<a class="reference internal" href="#binary"><span class="std std-ref">binary</span></a> arithmetic operations involving the <code class="docutils literal notranslate"><span class="pre">-</span></code> or <code class="docutils literal notranslate"><span class="pre">+</span></code>
operator.</p>
<p>Evaluation of a literal yields an object of the given type
(<a class="reference internal" href="../library/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>, <a class="reference internal" href="../library/functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate"><span class="pre">complex</span></code></a>, <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>,
<a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>, or <a class="reference internal" href="../library/string.templatelib.html#string.templatelib.Template" title="string.templatelib.Template"><code class="xref py py-class docutils literal notranslate"><span class="pre">Template</span></code></a>) with the given value.
The value may be approximated in the case of floating-point
and imaginary literals.</p>
<p>The formal grammar for literals is:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-literal">literal</strong>: <a class="reference internal" href="#grammar-token-python-grammar-strings"><code class="xref docutils literal notranslate"><span class="pre">strings</span></code></a> | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-NUMBER"><code class="xref docutils literal notranslate"><span class="pre">NUMBER</span></code></a>
</pre>
<section id="literals-and-object-identity">
<span id="index-7"></span><h4><span class="section-number">6.2.3.1. </span>Literals and object identity<a class="headerlink" href="#literals-and-object-identity" title="Link to this heading">¶</a></h4>
<p>All literals correspond to immutable data types, and hence the object's identity
is less important than its value. Multiple evaluations of literals with the
same value (either the same occurrence in the program text or a different
occurrence) may obtain the same object or a different object with the same
value.</p>
<div class="admonition-cpython-implementation-detail admonition">
<p class="admonition-title">CPython implementation detail</p>
<p>For example, in CPython, <em>small</em> integers with the same value evaluate
to the same object:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">>>> </span><span class="n">y</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">>>> </span><span class="n">x</span> <span class="ow">is</span> <span class="n">y</span>
<span class="go">True</span>
</pre></div>
</div>
<p>However, large integers evaluate to different objects:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="mi">123456789</span>
<span class="gp">>>> </span><span class="n">y</span> <span class="o">=</span> <span class="mi">123456789</span>
<span class="gp">>>> </span><span class="n">x</span> <span class="ow">is</span> <span class="n">y</span>
<span class="go">False</span>
</pre></div>
</div>
<p>This behavior may change in future versions of CPython.
In particular, the boundary between "small" and "large" integers has
already changed in the past.</p>
<p>CPython will emit a <a class="reference internal" href="../library/exceptions.html#SyntaxWarning" title="SyntaxWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxWarning</span></code></a> when you compare literals
using <code class="docutils literal notranslate"><span class="pre">is</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">x</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">>>> </span><span class="n">x</span> <span class="ow">is</span> <span class="mi">7</span>
<span class="go"><input>:1: SyntaxWarning: "is" with 'int' literal. Did you mean "=="?</span>
<span class="go">True</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="../faq/programming.html#faq-identity-with-is"><span class="std std-ref">When can I rely on identity tests with the is operator?</span></a> for more information.</p>
</div>
<p><a class="reference internal" href="lexical_analysis.html#t-strings"><span class="std std-ref">Template strings</span></a> are immutable but may reference mutable
objects as <a class="reference internal" href="../library/string.templatelib.html#string.templatelib.Interpolation" title="string.templatelib.Interpolation"><code class="xref py py-class docutils literal notranslate"><span class="pre">Interpolation</span></code></a> values.
For the purposes of this section, two t-strings have the "same value" if
both their structure and the <em>identity</em> of the values match.</p>
<div class="impl-detail compound">
<p><strong>جزئیات پیادهسازی در CPython:</strong> Currently, each evaluation of a template string results in
a different object.</p>
</div>
</section>
<section id="string-literal-concatenation">
<span id="string-concatenation"></span><h4><span class="section-number">6.2.3.2. </span>String literal concatenation<a class="headerlink" href="#string-literal-concatenation" title="Link to this heading">¶</a></h4>
<p>Multiple adjacent string or bytes literals, possibly
using different quoting conventions, are allowed, and their meaning is the same
as their concatenation:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="s2">"hello"</span> <span class="s1">'world'</span>
<span class="go">"helloworld"</span>
</pre></div>
</div>
<p>This feature is defined at the syntactical level, so it only works with literals.
To concatenate string expressions at run time, the '+' operator may be used:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">greeting</span> <span class="o">=</span> <span class="s2">"Hello"</span>
<span class="gp">>>> </span><span class="n">space</span> <span class="o">=</span> <span class="s2">" "</span>
<span class="gp">>>> </span><span class="n">name</span> <span class="o">=</span> <span class="s2">"Blaise"</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">greeting</span> <span class="o">+</span> <span class="n">space</span> <span class="o">+</span> <span class="n">name</span><span class="p">)</span> <span class="c1"># not: print(greeting space name)</span>
<span class="go">Hello Blaise</span>
</pre></div>
</div>
<p>Literal concatenation can freely mix raw strings, triple-quoted strings,
and formatted string literals.
For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="s2">"Hello"</span> <span class="sa">r</span><span class="s1">', '</span> <span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">!"</span>
<span class="go">"Hello, Blaise!"</span>
</pre></div>
</div>
<p>This feature can be used to reduce the number of backslashes
needed, to split long strings conveniently across long lines, or even to add
comments to parts of strings. For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"[A-Za-z_]"</span> <span class="c1"># letter or underscore</span>
<span class="s2">"[A-Za-z0-9_]*"</span> <span class="c1"># letter, digit or underscore</span>
<span class="p">)</span>
</pre></div>
</div>
<p>However, bytes literals may only be combined with other byte literals;
not with string literals of any kind.
Also, template string literals may only be combined with other template
string literals:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="sa">t</span><span class="s2">"Hello"</span> <span class="sa">t</span><span class="s2">"</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">!"</span>
<span class="go">Template(strings=('Hello', '!'), interpolations=(...))</span>
</pre></div>
</div>
<p>Formally:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-strings">strings</strong>: (<a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-STRING"><code class="xref docutils literal notranslate"><span class="pre">STRING</span></code></a> | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-fstring"><code class="xref docutils literal notranslate"><span class="pre">fstring</span></code></a>)+ | <a class="reference internal" href="lexical_analysis.html#grammar-token-python-grammar-tstring"><code class="xref docutils literal notranslate"><span class="pre">tstring</span></code></a>+
</pre>
</section>
</section>
<section id="parenthesized-forms">
<span id="parenthesized"></span><h3><span class="section-number">6.2.4. </span>Parenthesized forms<a class="headerlink" href="#parenthesized-forms" title="Link to this heading">¶</a></h3>
<p id="index-8">A parenthesized form is an optional expression list enclosed in parentheses:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-parenth_form">parenth_form</strong>: <span class="sx">"("</span> [<a class="reference internal" href="#grammar-token-python-grammar-starred_expression"><code class="xref docutils literal notranslate"><span class="pre">starred_expression</span></code></a>] <span class="sx">")"</span>
</pre>
<p>A parenthesized expression list yields whatever that expression list yields: if
the list contains at least one comma, it yields a tuple; otherwise, it yields
the single expression that makes up the expression list.</p>
<p id="index-9">An empty pair of parentheses yields an empty tuple object. Since tuples are
immutable, the same rules as for literals apply (i.e., two occurrences of the empty
tuple may or may not yield the same object).</p>
<p id="index-10">Note that tuples are not formed by the parentheses, but rather by use of the
comma. The exception is the empty tuple, for which parentheses <em>are</em>
required --- allowing unparenthesized "nothing" in expressions would cause
ambiguities and allow common typos to pass uncaught.</p>
</section>
<section id="displays-for-lists-sets-and-dictionaries">
<span id="comprehensions"></span><h3><span class="section-number">6.2.5. </span>Displays for lists, sets and dictionaries<a class="headerlink" href="#displays-for-lists-sets-and-dictionaries" title="Link to this heading">¶</a></h3>
<p id="index-11">For constructing a list, a set or a dictionary Python provides special syntax
called "displays", each of them in two flavors:</p>
<ul class="simple">
<li><p>either the container contents are listed explicitly, or</p></li>
<li><p>they are computed via a set of looping and filtering instructions, called a
<em class="dfn">comprehension</em>.</p></li>
</ul>
<p id="index-12">Common syntax elements for comprehensions are:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-comprehension">comprehension</strong>: <a class="reference internal" href="#grammar-token-python-grammar-assignment_expression"><code class="xref docutils literal notranslate"><span class="pre">assignment_expression</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a>
<strong id="grammar-token-python-grammar-comp_for">comp_for</strong>: [<span class="sx">"async"</span>] <span class="sx">"for"</span> <a class="reference internal" href="simple_stmts.html#grammar-token-python-grammar-target_list"><code class="xref docutils literal notranslate"><span class="pre">target_list</span></code></a> <span class="sx">"in"</span> <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> [<a class="reference internal" href="#grammar-token-python-grammar-comp_iter"><code class="xref docutils literal notranslate"><span class="pre">comp_iter</span></code></a>]
<strong id="grammar-token-python-grammar-comp_iter">comp_iter</strong>: <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-comp_if"><code class="xref docutils literal notranslate"><span class="pre">comp_if</span></code></a>
<strong id="grammar-token-python-grammar-comp_if">comp_if</strong>: <span class="sx">"if"</span> <a class="reference internal" href="#grammar-token-python-grammar-or_test"><code class="xref docutils literal notranslate"><span class="pre">or_test</span></code></a> [<a class="reference internal" href="#grammar-token-python-grammar-comp_iter"><code class="xref docutils literal notranslate"><span class="pre">comp_iter</span></code></a>]
</pre>
<p>The comprehension consists of a single expression followed by at least one
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause and zero or more <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">if</span></code> clauses.
In this case, the elements of the new container are those that would be produced
by considering each of the <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">if</span></code> clauses a block,
nesting from left to right, and evaluating the expression to produce an element
each time the innermost block is reached.</p>
<p>However, aside from the iterable expression in the leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause,
the comprehension is executed in a separate implicitly nested scope. This ensures
that names assigned to in the target list don't "leak" into the enclosing scope.</p>
<p>The iterable expression in the leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause is evaluated
directly in the enclosing scope and then passed as an argument to the implicitly
nested scope. Subsequent <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clauses and any filter condition in the
leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause cannot be evaluated in the enclosing scope as
they may depend on the values obtained from the leftmost iterable. For example:
<code class="docutils literal notranslate"><span class="pre">[x*y</span> <span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">range(10)</span> <span class="pre">for</span> <span class="pre">y</span> <span class="pre">in</span> <span class="pre">range(x,</span> <span class="pre">x+10)]</span></code>.</p>
<p>To ensure the comprehension always results in a container of the appropriate
type, <code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> expressions are prohibited in the implicitly
nested scope.</p>
<p id="index-13">Since Python 3.6, in an <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> function, an <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code>
clause may be used to iterate over a <a class="reference internal" href="../glossary.html#term-asynchronous-iterator"><span class="xref std std-term">asynchronous iterator</span></a>.
A comprehension in an <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code> function may consist of either a
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code> clause following the leading
expression, may contain additional <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> or <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code>
clauses, and may also use <a class="reference internal" href="#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code></a> expressions.</p>
<p>If a comprehension contains <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code> clauses, or if it contains
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code> expressions or other asynchronous comprehensions anywhere except
the iterable expression in the leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause, it is called an
<em class="dfn">asynchronous comprehension</em>. An asynchronous comprehension may suspend the
execution of the coroutine function in which it appears.
See also <span class="target" id="index-14"></span><a class="pep reference external" href="https://peps.python.org/pep-0530/"><strong>PEP 530</strong></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.6: </span>Asynchronous comprehensions were introduced.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.8: </span><code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> prohibited in the implicitly nested scope.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.11: </span>Asynchronous comprehensions are now allowed inside comprehensions in
asynchronous functions. Outer comprehensions implicitly become
asynchronous.</p>
</div>
</section>
<section id="list-displays">
<span id="lists"></span><h3><span class="section-number">6.2.6. </span>List displays<a class="headerlink" href="#list-displays" title="Link to this heading">¶</a></h3>
<p id="index-15">A list display is a possibly empty series of expressions enclosed in square
brackets:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-list_display">list_display</strong>: <span class="sx">"["</span> [<a class="reference internal" href="#grammar-token-python-grammar-flexible_expression_list"><code class="xref docutils literal notranslate"><span class="pre">flexible_expression_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-comprehension"><code class="xref docutils literal notranslate"><span class="pre">comprehension</span></code></a>] <span class="sx">"]"</span>
</pre>
<p>A list display yields a new list object, the contents being specified by either
a list of expressions or a comprehension. When a comma-separated list of
expressions is supplied, its elements are evaluated from left to right and
placed into the list object in that order. When a comprehension is supplied,
the list is constructed from the elements resulting from the comprehension.</p>
</section>
<section id="set-displays">
<span id="set"></span><h3><span class="section-number">6.2.7. </span>Set displays<a class="headerlink" href="#set-displays" title="Link to this heading">¶</a></h3>
<p id="index-16">A set display is denoted by curly braces and distinguishable from dictionary
displays by the lack of colons separating keys and values:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-set_display">set_display</strong>: <span class="sx">"{"</span> (<a class="reference internal" href="#grammar-token-python-grammar-flexible_expression_list"><code class="xref docutils literal notranslate"><span class="pre">flexible_expression_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-comprehension"><code class="xref docutils literal notranslate"><span class="pre">comprehension</span></code></a>) <span class="sx">"}"</span>
</pre>
<p>A set display yields a new mutable set object, the contents being specified by
either a sequence of expressions or a comprehension. When a comma-separated
list of expressions is supplied, its elements are evaluated from left to right
and added to the set object. When a comprehension is supplied, the set is
constructed from the elements resulting from the comprehension.</p>
<p>An empty set cannot be constructed with <code class="docutils literal notranslate"><span class="pre">{}</span></code>; this literal constructs an empty
dictionary.</p>
</section>
<section id="dictionary-displays">
<span id="dict"></span><h3><span class="section-number">6.2.8. </span>Dictionary displays<a class="headerlink" href="#dictionary-displays" title="Link to this heading">¶</a></h3>
<p id="index-17">A dictionary display is a possibly empty series of dict items (key/value pairs)
enclosed in curly braces:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-dict_display">dict_display</strong>: <span class="sx">"{"</span> [<a class="reference internal" href="#grammar-token-python-grammar-dict_item_list"><code class="xref docutils literal notranslate"><span class="pre">dict_item_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-dict_comprehension"><code class="xref docutils literal notranslate"><span class="pre">dict_comprehension</span></code></a>] <span class="sx">"}"</span>
<strong id="grammar-token-python-grammar-dict_item_list">dict_item_list</strong>: <a class="reference internal" href="#grammar-token-python-grammar-dict_item"><code class="xref docutils literal notranslate"><span class="pre">dict_item</span></code></a> (<span class="sx">","</span> <a class="reference internal" href="#grammar-token-python-grammar-dict_item"><code class="xref docutils literal notranslate"><span class="pre">dict_item</span></code></a>)* [<span class="sx">","</span>]
<strong id="grammar-token-python-grammar-dict_item">dict_item</strong>: <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <span class="sx">":"</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> | <span class="sx">"**"</span> <a class="reference internal" href="#grammar-token-python-grammar-or_expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a>
<strong id="grammar-token-python-grammar-dict_comprehension">dict_comprehension</strong>: <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <span class="sx">":"</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a>
</pre>
<p>A dictionary display yields a new dictionary object.</p>
<p>If a comma-separated sequence of dict items is given, they are evaluated
from left to right to define the entries of the dictionary: each key object is
used as a key into the dictionary to store the corresponding value. This means
that you can specify the same key multiple times in the dict item list, and the
final dictionary's value for that key will be the last one given.</p>
<p id="index-18">A double asterisk <code class="docutils literal notranslate"><span class="pre">**</span></code> denotes <em class="dfn">dictionary unpacking</em>.
Its operand must be a <a class="reference internal" href="../glossary.html#term-mapping"><span class="xref std std-term">mapping</span></a>. Each mapping item is added
to the new dictionary. Later values replace values already set by
earlier dict items and earlier dictionary unpackings.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.5: </span>Unpacking into dictionary displays, originally proposed by <span class="target" id="index-19"></span><a class="pep reference external" href="https://peps.python.org/pep-0448/"><strong>PEP 448</strong></a>.</p>
</div>
<p>A dict comprehension, in contrast to list and set comprehensions, needs two
expressions separated with a colon followed by the usual "for" and "if" clauses.
When the comprehension is run, the resulting key and value elements are inserted
in the new dictionary in the order they are produced.</p>
<p id="index-20">Restrictions on the types of the key values are listed earlier in section
<a class="reference internal" href="datamodel.html#types"><span class="std std-ref">The standard type hierarchy</span></a>. (To summarize, the key type should be <a class="reference internal" href="../glossary.html#term-hashable"><span class="xref std std-term">hashable</span></a>, which excludes
all mutable objects.) Clashes between duplicate keys are not detected; the last
value (textually rightmost in the display) stored for a given key value
prevails.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.8: </span>Prior to Python 3.8, in dict comprehensions, the evaluation order of key
and value was not well-defined. In CPython, the value was evaluated before
the key. Starting with 3.8, the key is evaluated before the value, as
proposed by <span class="target" id="index-21"></span><a class="pep reference external" href="https://peps.python.org/pep-0572/"><strong>PEP 572</strong></a>.</p>
</div>
</section>
<section id="generator-expressions">
<span id="genexpr"></span><h3><span class="section-number">6.2.9. </span>Generator expressions<a class="headerlink" href="#generator-expressions" title="Link to this heading">¶</a></h3>
<p id="index-22">A generator expression is a compact generator notation in parentheses:</p>
<pre class="highlight">
<strong id="grammar-token-python-grammar-generator_expression">generator_expression</strong>: <span class="sx">"("</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a> <a class="reference internal" href="#grammar-token-python-grammar-comp_for"><code class="xref docutils literal notranslate"><span class="pre">comp_for</span></code></a> <span class="sx">")"</span>
</pre>
<p>A generator expression yields a new generator object. Its syntax is the same as
for comprehensions, except that it is enclosed in parentheses instead of
brackets or curly braces.</p>
<p>Variables used in the generator expression are evaluated lazily when the
<a class="reference internal" href="#generator.__next__" title="generator.__next__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code></a> method is called for the generator object (in the same
fashion as normal generators). However, the iterable expression in the
leftmost <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause is immediately evaluated, and the
<a class="reference internal" href="../glossary.html#term-iterator"><span class="xref std std-term">iterator</span></a> is immediately created for that iterable, so that an error
produced while creating the iterator will be emitted at the point where the generator expression
is defined, rather than at the point where the first value is retrieved.
Subsequent <code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clauses and any filter condition in the leftmost
<code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code> clause cannot be evaluated in the enclosing scope as they may
depend on the values obtained from the leftmost iterable. For example:
<code class="docutils literal notranslate"><span class="pre">(x*y</span> <span class="pre">for</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">range(10)</span> <span class="pre">for</span> <span class="pre">y</span> <span class="pre">in</span> <span class="pre">range(x,</span> <span class="pre">x+10))</span></code>.</p>
<p>The parentheses can be omitted on calls with only one argument. See section
<a class="reference internal" href="#calls"><span class="std std-ref">Calls</span></a> for details.</p>
<p>To avoid interfering with the expected operation of the generator expression
itself, <code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> expressions are prohibited in the
implicitly defined generator.</p>
<p>If a generator expression contains either <code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code>
clauses or <a class="reference internal" href="#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code></a> expressions it is called an
<em class="dfn">asynchronous generator expression</em>. An asynchronous generator
expression returns a new asynchronous generator object,
which is an asynchronous iterator (see <a class="reference internal" href="datamodel.html#async-iterators"><span class="std std-ref">Asynchronous Iterators</span></a>).</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.6: </span>Asynchronous generator expressions were introduced.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.7: </span>Prior to Python 3.7, asynchronous generator expressions could
only appear in <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> coroutines. Starting
with 3.7, any function can use asynchronous generator expressions.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.8: </span><code class="docutils literal notranslate"><span class="pre">yield</span></code> and <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> prohibited in the implicitly nested scope.</p>
</div>
</section>
<section id="yield-expressions">
<span id="yieldexpr"></span><h3><span class="section-number">6.2.10. </span>Yield expressions<a class="headerlink" href="#yield-expressions" title="Link to this heading">¶</a></h3>
<pre class="highlight" id="index-23">
<strong id="grammar-token-python-grammar-yield_atom">yield_atom</strong>: <span class="sx">"("</span> <a class="reference internal" href="#grammar-token-python-grammar-yield_expression"><code class="xref docutils literal notranslate"><span class="pre">yield_expression</span></code></a> <span class="sx">")"</span>
<strong id="grammar-token-python-grammar-yield_from">yield_from</strong>: <span class="sx">"yield"</span> <span class="sx">"from"</span> <a class="reference internal" href="#grammar-token-python-grammar-expression"><code class="xref docutils literal notranslate"><span class="pre">expression</span></code></a>
<strong id="grammar-token-python-grammar-yield_expression">yield_expression</strong>: <span class="sx">"yield"</span> <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref docutils literal notranslate"><span class="pre">yield_list</span></code></a> | <a class="reference internal" href="#grammar-token-python-grammar-yield_from"><code class="xref docutils literal notranslate"><span class="pre">yield_from</span></code></a>
</pre>
<p>The yield expression is used when defining a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a> function
or an <a class="reference internal" href="../glossary.html#term-asynchronous-generator"><span class="xref std std-term">asynchronous generator</span></a> function and
thus can only be used in the body of a function definition. Using a yield
expression in a function's body causes that function to be a generator function,
and using it in an <a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> function's body causes that
coroutine function to be an asynchronous generator function. For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">gen</span><span class="p">():</span> <span class="c1"># defines a generator function</span>
<span class="k">yield</span> <span class="mi">123</span>
<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">agen</span><span class="p">():</span> <span class="c1"># defines an asynchronous generator function</span>
<span class="k">yield</span> <span class="mi">123</span>
</pre></div>
</div>
<p>Due to their side effects on the containing scope, <code class="docutils literal notranslate"><span class="pre">yield</span></code> expressions
are not permitted as part of the implicitly defined scopes used to
implement comprehensions and generator expressions.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.8: </span>Yield expressions prohibited in the implicitly nested scopes used to
implement comprehensions and generator expressions.</p>
</div>
<p>Generator functions are described below, while asynchronous generator
functions are described separately in section
<a class="reference internal" href="#asynchronous-generator-functions"><span class="std std-ref">Asynchronous generator functions</span></a>.</p>
<p>When a generator function is called, it returns an iterator known as a
generator. That generator then controls the execution of the generator
function. The execution starts when one of the generator's methods is called.
At that time, the execution proceeds to the first yield expression, where it is
suspended again, returning the value of <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a>
to the generator's caller,
or <code class="docutils literal notranslate"><span class="pre">None</span></code> if <code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code> is omitted.
By suspended, we mean that all local state is
retained, including the current bindings of local variables, the instruction
pointer, the internal evaluation stack, and the state of any exception handling.
When the execution is resumed by calling one of the generator's methods, the
function can proceed exactly as if the yield expression were just another
external call. The value of the yield expression after resuming depends on the
method which resumed the execution. If <a class="reference internal" href="#generator.__next__" title="generator.__next__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code></a> is used
(typically via either a <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> or the <a class="reference internal" href="../library/functions.html#next" title="next"><code class="xref py py-func docutils literal notranslate"><span class="pre">next()</span></code></a> builtin) then the
result is <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>. Otherwise, if <a class="reference internal" href="#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a> is used, then
the result will be the value passed in to that method.</p>
<p id="index-24">All of this makes generator functions quite similar to coroutines; they yield
multiple times, they have more than one entry point and their execution can be
suspended. The only difference is that a generator function cannot control
where the execution should continue after it yields; the control is always
transferred to the generator's caller.</p>
<p>Yield expressions are allowed anywhere in a <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> construct. If the
generator is not resumed before it is
finalized (by reaching a zero reference count or by being garbage collected),
the generator-iterator's <a class="reference internal" href="#generator.close" title="generator.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method will be called,
allowing any pending <a class="reference internal" href="compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> clauses to execute.</p>
<p id="index-25">When <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre"><expr></span></code> is used, the supplied expression must be an
iterable. The values produced by iterating that iterable are passed directly
to the caller of the current generator's methods. Any values passed in with
<a class="reference internal" href="#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a> and any exceptions passed in with
<a class="reference internal" href="#generator.throw" title="generator.throw"><code class="xref py py-meth docutils literal notranslate"><span class="pre">throw()</span></code></a> are passed to the underlying iterator if it has the
appropriate methods. If this is not the case, then <code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code>
will raise <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">AttributeError</span></code></a> or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>, while
<code class="xref py py-meth docutils literal notranslate"><span class="pre">throw()</span></code> will just raise the passed in exception immediately.</p>
<p>When the underlying iterator is complete, the <a class="reference internal" href="../library/exceptions.html#StopIteration.value" title="StopIteration.value"><code class="xref py py-attr docutils literal notranslate"><span class="pre">value</span></code></a>
attribute of the raised <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> instance becomes the value of
the yield expression. It can be either set explicitly when raising
<code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code>, or automatically when the subiterator is a generator
(by returning a value from the subgenerator).</p>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.3: </span>Added <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre"><expr></span></code> to delegate control flow to a subiterator.</p>
</div>
<p>The parentheses may be omitted when the yield expression is the sole expression
on the right hand side of an assignment statement.</p>
<div class="admonition seealso">
<p class="admonition-title">همچنین ملاحظه نمائید</p>
<dl class="simple">
<dt><span class="target" id="index-26"></span><a class="pep reference external" href="https://peps.python.org/pep-0255/"><strong>PEP 255</strong></a> - Simple Generators</dt><dd><p>The proposal for adding generators and the <a class="reference internal" href="simple_stmts.html#yield"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">yield</span></code></a> statement to Python.</p>
</dd>
<dt><span class="target" id="index-27"></span><a class="pep reference external" href="https://peps.python.org/pep-0342/"><strong>PEP 342</strong></a> - Coroutines via Enhanced Generators</dt><dd><p>The proposal to enhance the API and syntax of generators, making them
usable as simple coroutines.</p>
</dd>
<dt><span class="target" id="index-28"></span><a class="pep reference external" href="https://peps.python.org/pep-0380/"><strong>PEP 380</strong></a> - Syntax for Delegating to a Subgenerator</dt><dd><p>The proposal to introduce the <a class="reference internal" href="#grammar-token-python-grammar-yield_from"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_from</span></code></a> syntax,
making delegation to subgenerators easy.</p>
</dd>
<dt><span class="target" id="index-29"></span><a class="pep reference external" href="https://peps.python.org/pep-0525/"><strong>PEP 525</strong></a> - Asynchronous Generators</dt><dd><p>The proposal that expanded on <span class="target" id="index-30"></span><a class="pep reference external" href="https://peps.python.org/pep-0492/"><strong>PEP 492</strong></a> by adding generator capabilities to
coroutine functions.</p>
</dd>
</dl>
</div>
<section id="generator-iterator-methods">
<span id="generator-methods"></span><span id="index-31"></span><h4><span class="section-number">6.2.10.1. </span>Generator-iterator methods<a class="headerlink" href="#generator-iterator-methods" title="Link to this heading">¶</a></h4>
<p>This subsection describes the methods of a generator iterator. They can
be used to control the execution of a generator function.</p>
<p>Note that calling any of the generator methods below when the generator
is already executing raises a <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> exception.</p>
<dl class="py method" id="index-32">
<dt class="sig sig-object py" id="generator.__next__">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">__next__</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#generator.__next__" title="Link to this definition">¶</a></dt>
<dd><p>Starts the execution of a generator function or resumes it at the last
executed yield expression. When a generator function is resumed with a
<code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code> method, the current yield expression always
evaluates to <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>. The execution then continues to the next yield
expression, where the generator is suspended again, and the value of the
<a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a> is returned to <code class="xref py py-meth docutils literal notranslate"><span class="pre">__next__()</span></code>'s
caller. If the generator exits without yielding another value, a
<a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception is raised.</p>
<p>This method is normally called implicitly, e.g. by a <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> loop, or
by the built-in <a class="reference internal" href="../library/functions.html#next" title="next"><code class="xref py py-func docutils literal notranslate"><span class="pre">next()</span></code></a> function.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="generator.send">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">send</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#generator.send" title="Link to this definition">¶</a></dt>
<dd><p>Resumes the execution and "sends" a value into the generator function. The
<em>value</em> argument becomes the result of the current yield expression. The
<code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code> method returns the next value yielded by the generator, or
raises <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> if the generator exits without yielding another
value. When <code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code> is called to start the generator, it must be called
with <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as the argument, because there is no yield expression that
could receive the value.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="generator.throw">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">throw</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#generator.throw" title="Link to this definition">¶</a></dt>
<dt class="sig sig-object py">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">throw</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">type</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">traceback</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span></dt>
<dd><p>Raises an exception at the point where the generator was paused,
and returns the next value yielded by the generator function. If the generator
exits without yielding another value, a <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception is
raised. If the generator function does not catch the passed-in exception, or
raises a different exception, then that exception propagates to the caller.</p>
<p>In typical use, this is called with a single exception instance similar to the
way the <a class="reference internal" href="simple_stmts.html#raise"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">raise</span></code></a> keyword is used.</p>
<p>For backwards compatibility, however, the second signature is
supported, following a convention from older versions of Python.
The <em>type</em> argument should be an exception class, and <em>value</em>
should be an exception instance. If the <em>value</em> is not provided, the
<em>type</em> constructor is called to get an instance. If <em>traceback</em>
is provided, it is set on the exception, otherwise any existing
<a class="reference internal" href="../library/exceptions.html#BaseException.__traceback__" title="BaseException.__traceback__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__traceback__</span></code></a> attribute stored in <em>value</em> may
be cleared.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.12: </span>The second signature (type[, value[, traceback]]) is deprecated and
may be removed in a future version of Python.</p>
</div>
</dd></dl>
<dl class="py method" id="index-33">
<dt class="sig sig-object py" id="generator.close">
<span class="sig-prename descclassname"><span class="pre">generator.</span></span><span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#generator.close" title="Link to this definition">¶</a></dt>
<dd><p>Raises a <a class="reference internal" href="../library/exceptions.html#GeneratorExit" title="GeneratorExit"><code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code></a> exception at the point where the generator
function was paused (equivalent to calling <code class="docutils literal notranslate"><span class="pre">throw(GeneratorExit)</span></code>).
The exception is raised by the yield expression where the generator was paused.
If the generator function catches the exception and returns a
value, this value is returned from <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code>. If the generator function
is already closed, or raises <code class="xref py py-exc docutils literal notranslate"><span class="pre">GeneratorExit</span></code> (by not catching the
exception), <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code> returns <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>. If the generator yields a
value, a <a class="reference internal" href="../library/exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> is raised. If the generator raises any other
exception, it is propagated to the caller. If the generator has already
exited due to an exception or normal exit, <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code> returns
<code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code> and has no other effect.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.13: </span>If a generator returns a value upon being closed, the value is returned
by <code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code>.</p>
</div>
</dd></dl>
</section>
<section id="examples">
<span id="index-34"></span><h4><span class="section-number">6.2.10.2. </span>Examples<a class="headerlink" href="#examples" title="Link to this heading">¶</a></h4>
<p>Here is a simple example that demonstrates the behavior of generators and
generator functions:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span><span class="w"> </span><span class="nf">echo</span><span class="p">(</span><span class="n">value</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Execution starts when 'next()' is called for the first time."</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">try</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">try</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">value</span> <span class="o">=</span> <span class="p">(</span><span class="k">yield</span> <span class="n">value</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">except</span> <span class="ne">Exception</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">value</span> <span class="o">=</span> <span class="n">e</span>
<span class="gp">... </span> <span class="k">finally</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"Don't forget to clean up when 'close()' is called."</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">generator</span> <span class="o">=</span> <span class="n">echo</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">generator</span><span class="p">))</span>
<span class="go">Execution starts when 'next()' is called for the first time.</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">generator</span><span class="p">))</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">generator</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span>
<span class="go">2</span>
<span class="gp">>>> </span><span class="n">generator</span><span class="o">.</span><span class="n">throw</span><span class="p">(</span><span class="ne">TypeError</span><span class="p">,</span> <span class="s2">"spam"</span><span class="p">)</span>
<span class="go">TypeError('spam',)</span>
<span class="gp">>>> </span><span class="n">generator</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="go">Don't forget to clean up when 'close()' is called.</span>
</pre></div>
</div>
<p>For examples using <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code>, see <a class="reference internal" href="../whatsnew/3.3.html#pep-380"><span class="std std-ref">PEP 380: Syntax for Delegating to a Subgenerator</span></a> in "What's New in
Python."</p>
</section>
<section id="asynchronous-generator-functions">
<span id="id4"></span><h4><span class="section-number">6.2.10.3. </span>Asynchronous generator functions<a class="headerlink" href="#asynchronous-generator-functions" title="Link to this heading">¶</a></h4>
<p>The presence of a yield expression in a function or method defined using
<a class="reference internal" href="compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> further defines the function as an
<a class="reference internal" href="../glossary.html#term-asynchronous-generator"><span class="xref std std-term">asynchronous generator</span></a> function.</p>
<p>When an asynchronous generator function is called, it returns an
asynchronous iterator known as an asynchronous generator object.
That object then controls the execution of the generator function.
An asynchronous generator object is typically used in an
<a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> statement in a coroutine function analogously to
how a generator object would be used in a <a class="reference internal" href="compound_stmts.html#for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">for</span></code></a> statement.</p>
<p>Calling one of the asynchronous generator's methods returns an <a class="reference internal" href="../glossary.html#term-awaitable"><span class="xref std std-term">awaitable</span></a>
object, and the execution starts when this object is awaited on. At that time,
the execution proceeds to the first yield expression, where it is suspended
again, returning the value of <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a> to the
awaiting coroutine. As with a generator, suspension means that all local state
is retained, including the current bindings of local variables, the instruction
pointer, the internal evaluation stack, and the state of any exception handling.
When the execution is resumed by awaiting on the next object returned by the
asynchronous generator's methods, the function can proceed exactly as if the
yield expression were just another external call. The value of the yield
expression after resuming depends on the method which resumed the execution. If
<a class="reference internal" href="#agen.__anext__" title="agen.__anext__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__anext__()</span></code></a> is used then the result is <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>. Otherwise, if
<a class="reference internal" href="#agen.asend" title="agen.asend"><code class="xref py py-meth docutils literal notranslate"><span class="pre">asend()</span></code></a> is used, then the result will be the value passed in to that
method.</p>
<p>If an asynchronous generator happens to exit early by <a class="reference internal" href="simple_stmts.html#break"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">break</span></code></a>, the caller
task being cancelled, or other exceptions, the generator's async cleanup code
will run and possibly raise exceptions or access context variables in an
unexpected context--perhaps after the lifetime of tasks it depends, or
during the event loop shutdown when the async-generator garbage collection hook
is called.
To prevent this, the caller must explicitly close the async generator by calling
<a class="reference internal" href="#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code></a> method to finalize the generator and ultimately detach it
from the event loop.</p>
<p>In an asynchronous generator function, yield expressions are allowed anywhere
in a <a class="reference internal" href="compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> construct. However, if an asynchronous generator is not
resumed before it is finalized (by reaching a zero reference count or by
being garbage collected), then a yield expression within a <code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code>
construct could result in a failure to execute pending <a class="reference internal" href="compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a>
clauses. In this case, it is the responsibility of the event loop or
scheduler running the asynchronous generator to call the asynchronous
generator-iterator's <a class="reference internal" href="#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code></a> method and run the resulting
coroutine object, thus allowing any pending <code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code> clauses
to execute.</p>
<p>To take care of finalization upon event loop termination, an event loop should
define a <em>finalizer</em> function which takes an asynchronous generator-iterator and
presumably calls <a class="reference internal" href="#agen.aclose" title="agen.aclose"><code class="xref py py-meth docutils literal notranslate"><span class="pre">aclose()</span></code></a> and executes the coroutine.
This <em>finalizer</em> may be registered by calling <a class="reference internal" href="../library/sys.html#sys.set_asyncgen_hooks" title="sys.set_asyncgen_hooks"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.set_asyncgen_hooks()</span></code></a>.
When first iterated over, an asynchronous generator-iterator will store the
registered <em>finalizer</em> to be called upon finalization. For a reference example
of a <em>finalizer</em> method see the implementation of
<code class="docutils literal notranslate"><span class="pre">asyncio.Loop.shutdown_asyncgens</span></code> in <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.14/Lib/asyncio/base_events.py">Lib/asyncio/base_events.py</a>.</p>
<p>The expression <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span> <span class="pre"><expr></span></code> is a syntax error when used in an
asynchronous generator function.</p>
</section>
<section id="asynchronous-generator-iterator-methods">
<span id="asynchronous-generator-methods"></span><span id="index-35"></span><h4><span class="section-number">6.2.10.4. </span>Asynchronous generator-iterator methods<a class="headerlink" href="#asynchronous-generator-iterator-methods" title="Link to this heading">¶</a></h4>
<p>This subsection describes the methods of an asynchronous generator iterator,
which are used to control the execution of a generator function.</p>
<dl class="py method" id="index-36">
<dt class="sig sig-object py" id="agen.__anext__">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">__anext__</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#agen.__anext__" title="Link to this definition">¶</a></dt>
<dd><p>Returns an awaitable which when run starts to execute the asynchronous
generator or resumes it at the last executed yield expression. When an
asynchronous generator function is resumed with an <code class="xref py py-meth docutils literal notranslate"><span class="pre">__anext__()</span></code>
method, the current yield expression always evaluates to <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> in the
returned awaitable, which when run will continue to the next yield
expression. The value of the <a class="reference internal" href="#grammar-token-python-grammar-yield_list"><code class="xref std std-token docutils literal notranslate"><span class="pre">yield_list</span></code></a> of the
yield expression is the value of the <a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception raised by
the completing coroutine. If the asynchronous generator exits without
yielding another value, the awaitable instead raises a
<a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> exception, signalling that the asynchronous
iteration has completed.</p>
<p>This method is normally called implicitly by a <a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> loop.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="agen.asend">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">asend</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#agen.asend" title="Link to this definition">¶</a></dt>
<dd><p>Returns an awaitable which when run resumes the execution of the
asynchronous generator. As with the <a class="reference internal" href="#generator.send" title="generator.send"><code class="xref py py-meth docutils literal notranslate"><span class="pre">send()</span></code></a> method for a
generator, this "sends" a value into the asynchronous generator function,
and the <em>value</em> argument becomes the result of the current yield expression.
The awaitable returned by the <code class="xref py py-meth docutils literal notranslate"><span class="pre">asend()</span></code> method will return the next
value yielded by the generator as the value of the raised
<a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a>, or raises <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> if the
asynchronous generator exits without yielding another value. When
<code class="xref py py-meth docutils literal notranslate"><span class="pre">asend()</span></code> is called to start the asynchronous
generator, it must be called with <a class="reference internal" href="../library/constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as the argument,
because there is no yield expression that could receive the value.</p>
</dd></dl>
<dl class="py method">
<dt class="sig sig-object py" id="agen.athrow">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">athrow</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#agen.athrow" title="Link to this definition">¶</a></dt>
<dt class="sig sig-object py">
<em class="property"><span class="k"><span class="pre">async</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">agen.</span></span><span class="sig-name descname"><span class="pre">athrow</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">type</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">value</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">traceback</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span></dt>
<dd><p>Returns an awaitable that raises an exception of type <code class="docutils literal notranslate"><span class="pre">type</span></code> at the point
where the asynchronous generator was paused, and returns the next value
yielded by the generator function as the value of the raised
<a class="reference internal" href="../library/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> exception. If the asynchronous generator exits
without yielding another value, a <a class="reference internal" href="../library/exceptions.html#StopAsyncIteration" title="StopAsyncIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopAsyncIteration</span></code></a> exception is
raised by the awaitable.
If the generator function does not catch the passed-in exception, or
raises a different exception, then when the awaitable is run that exception
propagates to the caller of the awaitable.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">تغییر داده شده در نسخه 3.12: </span>The second signature (type[, value[, traceback]]) is deprecated and
may be removed in a future version of Python.</p>
</div>