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<!DOCTYPE html>

<head>

<title>What’s New In Python 3.10 — Python 3.11.5 belgelendirmesi</title><meta name="viewport" content="width=device-width, initial-scale=1.0">

title="Python 3.11.5 belgelendirmesi içinde ara"

href="../_static/opensearch.xml"/>

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<h3><a href="../contents.html">İçindekiler</a></h3>

<ul>

<li><a class="reference internal" href="#">What’s New In Python 3.10</a><ul>

<li><a class="reference internal" href="#summary-release-highlights">Summary – Release highlights</a></li>

<li><a class="reference internal" href="#new-features">New Features</a><ul>

<li><a class="reference internal" href="#parenthesized-context-managers">Parenthesized context managers</a></li>

<li><a class="reference internal" href="#better-error-messages">Better error messages</a><ul>

<li><a class="reference internal" href="#syntaxerrors">SyntaxErrors</a></li>

<li><a class="reference internal" href="#indentationerrors">IndentationErrors</a></li>

<li><a class="reference internal" href="#attributeerrors">AttributeErrors</a></li>

<li><a class="reference internal" href="#nameerrors">NameErrors</a></li>

</ul>

</li>

<li><a class="reference internal" href="#pep-626-precise-line-numbers-for-debugging-and-other-tools">PEP 626: Precise line numbers for debugging and other tools</a></li>

<li><a class="reference internal" href="#pep-634-structural-pattern-matching">PEP 634: Structural Pattern Matching</a><ul>

<li><a class="reference internal" href="#syntax-and-operations">Syntax and operations</a></li>

<li><a class="reference internal" href="#declarative-approach">Declarative approach</a></li>

<li><a class="reference internal" href="#simple-pattern-match-to-a-literal">Simple pattern: match to a literal</a><ul>

<li><a class="reference internal" href="#behavior-without-the-wildcard">Behavior without the wildcard</a></li>

</ul>

</li>

<li><a class="reference internal" href="#patterns-with-a-literal-and-variable">Patterns with a literal and variable</a></li>

<li><a class="reference internal" href="#patterns-and-classes">Patterns and classes</a><ul>

<li><a class="reference internal" href="#patterns-with-positional-parameters">Patterns with positional parameters</a></li>

</ul>

</li>

<li><a class="reference internal" href="#nested-patterns">Nested patterns</a></li>

<li><a class="reference internal" href="#complex-patterns-and-the-wildcard">Complex patterns and the wildcard</a></li>

<li><a class="reference internal" href="#guard">Guard</a></li>

<li><a class="reference internal" href="#other-key-features">Other Key Features</a></li>

</ul>

</li>

<li><a class="reference internal" href="#optional-encodingwarning-and-encoding-locale-option">Optional <code class="docutils literal notranslate">EncodingWarning</code> and <code class="docutils literal notranslate">encoding="locale"</code> option</a></li>

</ul>

</li>

<li><a class="reference internal" href="#new-features-related-to-type-hints">New Features Related to Type Hints</a><ul>

<li><a class="reference internal" href="#pep-604-new-type-union-operator">PEP 604: New Type Union Operator</a></li>

<li><a class="reference internal" href="#pep-612-parameter-specification-variables">PEP 612: Parameter Specification Variables</a></li>

<li><a class="reference internal" href="#pep-613-typealias">PEP 613: TypeAlias</a></li>

<li><a class="reference internal" href="#pep-647-user-defined-type-guards">PEP 647: User-Defined Type Guards</a></li>

</ul>

</li>

<li><a class="reference internal" href="#other-language-changes">Other Language Changes</a></li>

<li><a class="reference internal" href="#new-modules">New Modules</a></li>

<li><a class="reference internal" href="#improved-modules">Improved Modules</a><ul>

<li><a class="reference internal" href="#asyncio">asyncio</a></li>

<li><a class="reference internal" href="#argparse">argparse</a></li>

<li><a class="reference internal" href="#array">array</a></li>

<li><a class="reference internal" href="#asynchat-asyncore-smtpd">asynchat, asyncore, smtpd</a></li>

<li><a class="reference internal" href="#bisect">bisect</a></li>

<li><a class="reference internal" href="#codecs">codecs</a></li>

<li><a class="reference internal" href="#collections-abc">collections.abc</a></li>

<li><a class="reference internal" href="#contextlib">contextlib</a></li>

<li><a class="reference internal" href="#curses">curses</a></li>

<li><a class="reference internal" href="#dataclasses">dataclasses</a><ul>

<li><a class="reference internal" href="#slots">__slots__</a></li>

<li><a class="reference internal" href="#keyword-only-fields">Keyword-only fields</a></li>

</ul>

</li>

<li><a class="reference internal" href="#distutils">distutils</a></li>

<li><a class="reference internal" href="#doctest">doctest</a></li>

<li><a class="reference internal" href="#encodings">encodings</a></li>

<li><a class="reference internal" href="#fileinput">fileinput</a></li>

<li><a class="reference internal" href="#faulthandler">faulthandler</a></li>

<li><a class="reference internal" href="#hashlib">hashlib</a></li>

<li><a class="reference internal" href="#idle-and-idlelib">IDLE and idlelib</a></li>

<li><a class="reference internal" href="#importlib-metadata">importlib.metadata</a></li>

<li><a class="reference internal" href="#inspect">inspect</a></li>

<li><a class="reference internal" href="#itertools">itertools</a></li>

<li><a class="reference internal" href="#linecache">linecache</a></li>

<li><a class="reference internal" href="#pathlib">pathlib</a></li>

<li><a class="reference internal" href="#platform">platform</a></li>

<li><a class="reference internal" href="#pprint">pprint</a></li>

<li><a class="reference internal" href="#py-compile">py_compile</a></li>

<li><a class="reference internal" href="#pyclbr">pyclbr</a></li>

<li><a class="reference internal" href="#shelve">shelve</a></li>

<li><a class="reference internal" href="#statistics">statistics</a></li>

<li><a class="reference internal" href="#socket">socket</a></li>

<li><a class="reference internal" href="#sqlite3">sqlite3</a></li>

<li><a class="reference internal" href="#thread">_thread</a></li>

<li><a class="reference internal" href="#threading">threading</a></li>

<li><a class="reference internal" href="#traceback">traceback</a></li>

<li><a class="reference internal" href="#types">types</a></li>

<li><a class="reference internal" href="#typing">typing</a></li>

<li><a class="reference internal" href="#unittest">unittest</a></li>

<li><a class="reference internal" href="#urllib-parse">urllib.parse</a></li>

<li><a class="reference internal" href="#zipimport">zipimport</a></li>

</ul>

</li>

<li><a class="reference internal" href="#optimizations">Optimizations</a></li>

<li><a class="reference internal" href="#deprecated">Deprecated</a></li>

<li><a class="reference internal" href="#removed">Removed</a></li>

<li><a class="reference internal" href="#porting-to-python-3-10">Porting to Python 3.10</a><ul>

<li><a class="reference internal" href="#changes-in-the-python-syntax">Changes in the Python syntax</a></li>

<li><a class="reference internal" href="#changes-in-the-python-api">Changes in the Python API</a></li>

<li><a class="reference internal" href="#changes-in-the-c-api">Changes in the C API</a></li>

</ul>

</li>

<li><a class="reference internal" href="#cpython-bytecode-changes">CPython bytecode changes</a></li>

<li><a class="reference internal" href="#build-changes">Build Changes</a></li>

<li><a class="reference internal" href="#c-api-changes">C API Changes</a><ul>

<li><a class="reference internal" href="#pep-652-maintaining-the-stable-abi">PEP 652: Maintaining the Stable ABI</a></li>

<li><a class="reference internal" href="#id1">New Features</a></li>

<li><a class="reference internal" href="#id2">Porting to Python 3.10</a></li>

<li><a class="reference internal" href="#id3">Deprecated</a></li>

<li><a class="reference internal" href="#id4">Removed</a></li>

</ul>

</li>

</ul>

</li>

</ul>

</div>

<div>

<h4>Önceki konu</h4>

<a href="3.11.html"

title="önceki bölüm">What’s New In Python 3.11</a>

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<h4>Sonraki konu</h4>

<a href="3.9.html"

title="sonraki bölüm">Python 3.9’daki Yenilikler</a>

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<h3>Bu Sayfa</h3>

<li><a href="../bugs.html">Hata Bildir</a></li>

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<a href="https://github.com/python/cpython/blob/3.11/Doc/whatsnew/3.10.rst"

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<h3>Gezinti</h3>

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<h1>What’s New In Python 3.10<a class="headerlink" href="#what-s-new-in-python-3-10" title="Permalink to this heading">¶</a></h1>

<dt class="field-odd">Editor:</dt>

<dd class="field-odd">Pablo Galindo Salgado

</dd>

</dl>

This article explains the new features in Python 3.10, compared to 3.9.

Python 3.10 was released on October 4, 2021.

For full details, see the <a class="reference internal" href="changelog.html#changelog">changelog</a>.

<h2>Summary – Release highlights<a class="headerlink" href="#summary-release-highlights" title="Permalink to this heading">¶</a></h2>

New syntax features:

<li><a class="pep reference external" href="https://peps.python.org/pep-0634/">PEP 634</a>, Structural Pattern Matching: Specification</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0635/">PEP 635</a>, Structural Pattern Matching: Motivation and Rationale</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0636/">PEP 636</a>, Structural Pattern Matching: Tutorial</li>

<li><a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=12782">bpo-12782</a>, Parenthesized context managers are now officially allowed.</li>

</ul>

New features in the standard library:

<li><a class="pep reference external" href="https://peps.python.org/pep-0618/">PEP 618</a>, Add Optional Length-Checking To zip.</li>

</ul>

Interpreter improvements:

<li><a class="pep reference external" href="https://peps.python.org/pep-0626/">PEP 626</a>, Precise line numbers for debugging and other tools.</li>

</ul>

New typing features:

<li><a class="pep reference external" href="https://peps.python.org/pep-0604/">PEP 604</a>, Allow writing union types as X | Y</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a>, Parameter Specification Variables</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0613/">PEP 613</a>, Explicit Type Aliases</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0647/">PEP 647</a>, User-Defined Type Guards</li>

</ul>

Important deprecations, removals or restrictions:

<li><a class="pep reference external" href="https://peps.python.org/pep-0644/">PEP 644</a>, Require OpenSSL 1.1.1 or newer</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0632/">PEP 632</a>, Deprecate distutils module.</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0623/">PEP 623</a>, Deprecate and prepare for the removal of the wstr member in PyUnicodeObject.</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0624/">PEP 624</a>, Remove Py_UNICODE encoder APIs</li>

<li><a class="pep reference external" href="https://peps.python.org/pep-0597/">PEP 597</a>, Add optional EncodingWarning</li>

</ul>

</section>

<h2>New Features<a class="headerlink" href="#new-features" title="Permalink to this heading">¶</a></h2>

<h3>Parenthesized context managers<a class="headerlink" href="#parenthesized-context-managers" title="Permalink to this heading">¶</a></h3>

Using enclosing parentheses for continuation across multiple lines

in context managers is now supported. This allows formatting a long

collection of context managers in multiple lines in a similar way

as it was previously possible with import statements. For instance,

all these examples are now valid:

<div class="highlight-python notranslate"><div class="highlight"><pre>with (CtxManager() as example):

...

with (

CtxManager1(),

CtxManager2()

):

...

with (CtxManager1() as example,

CtxManager2()):

...

with (CtxManager1(),

CtxManager2() as example):

...

with (

CtxManager1() as example1,

CtxManager2() as example2

):

...

</pre></div>

</div>

it is also possible to use a trailing comma at the end of the

enclosed group:

<div class="highlight-python notranslate"><div class="highlight"><pre>with (

CtxManager1() as example1,

CtxManager2() as example2,

CtxManager3() as example3,

):

...

</pre></div>

</div>

This new syntax uses the non LL(1) capacities of the new parser.

Check <a class="pep reference external" href="https://peps.python.org/pep-0617/">PEP 617</a> for more details.

(Contributed by Guido van Rossum, Pablo Galindo and Lysandros Nikolaou

in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=12782">bpo-12782</a> and <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=40334">bpo-40334</a>.)

</section>

<h3>Better error messages<a class="headerlink" href="#better-error-messages" title="Permalink to this heading">¶</a></h3>

<h4>SyntaxErrors<a class="headerlink" href="#syntaxerrors" title="Permalink to this heading">¶</a></h4>

When parsing code that contains unclosed parentheses or brackets the interpreter

now includes the location of the unclosed bracket of parentheses instead of displaying

SyntaxError: unexpected EOF while parsing or pointing to some incorrect location.

For instance, consider the following code (notice the unclosed ‘{‘):

<div class="highlight-python notranslate"><div class="highlight"><pre>expected = {9: 1, 18: 2, 19: 2, 27: 3, 28: 3, 29: 3, 36: 4, 37: 4,

38: 4, 39: 4, 45: 5, 46: 5, 47: 5, 48: 5, 49: 5, 54: 6,

some_other_code = foo()

</pre></div>

</div>

Previous versions of the interpreter reported confusing places as the location of

the syntax error:

<div class="highlight-python notranslate"><div class="highlight"><pre>File "example.py", line 3

some_other_code = foo()

^

SyntaxError: invalid syntax

</pre></div>

</div>

but in Python 3.10 a more informative error is emitted:

expected = {9: 1, 18: 2, 19: 2, 27: 3, 28: 3, 29: 3, 36: 4, 37: 4,

^

SyntaxError: '{' was never closed

</pre></div>

</div>

In a similar way, errors involving unclosed string literals (single and triple

quoted) now point to the start of the string instead of reporting EOF/EOL.

These improvements are inspired by previous work in the PyPy interpreter.

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=42864">bpo-42864</a> and Batuhan Taskaya in

<a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=40176">bpo-40176</a>.)

<a class="reference internal" href="../library/exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate">SyntaxError</code></a> exceptions raised by the interpreter will now highlight the

full error range of the expression that constitutes the syntax error itself,

instead of just where the problem is detected. In this way, instead of displaying

(before Python 3.10):

<div class="highlight-python notranslate"><div class="highlight"><pre>>>> foo(x, z for z in range(10), t, w)

File "<stdin>", line 1

foo(x, z for z in range(10), t, w)

^

SyntaxError: Generator expression must be parenthesized

</pre></div>

</div>

now Python 3.10 will display the exception as:

File "<stdin>", line 1

^^^^^^^^^^^^^^^^^^^^

SyntaxError: Generator expression must be parenthesized

</pre></div>

</div>

This improvement was contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43914">bpo-43914</a>.

A considerable amount of new specialized messages for <a class="reference internal" href="../library/exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate">SyntaxError</code></a> exceptions

have been incorporated. Some of the most notable ones are as follows:

<ul>

<li>Missing <code class="docutils literal notranslate">:</code> before blocks:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> if rocket.position > event_horizon

File "<stdin>", line 1

if rocket.position > event_horizon

^

SyntaxError: expected ':'

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=42997">bpo-42997</a>.)

</div></blockquote>

</li>

<li>Unparenthesised tuples in comprehensions targets:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> {x,y for x,y in zip('abcd', '1234')}

File "<stdin>", line 1

{x,y for x,y in zip('abcd', '1234')}

^

SyntaxError: did you forget parentheses around the comprehension target?

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43017">bpo-43017</a>.)

</div></blockquote>

</li>

<li>Missing commas in collection literals and between expressions:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> items = {

... x: 1,

... y: 2

... z: 3,

File "<stdin>", line 3

y: 2

^

SyntaxError: invalid syntax. Perhaps you forgot a comma?

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43822">bpo-43822</a>.)

</div></blockquote>

</li>

<li>Multiple Exception types without parentheses:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> try:

... build_dyson_sphere()

... except NotEnoughScienceError, NotEnoughResourcesError:

File "<stdin>", line 3

except NotEnoughScienceError, NotEnoughResourcesError:

^

SyntaxError: multiple exception types must be parenthesized

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43149">bpo-43149</a>.)

</div></blockquote>

</li>

<li>Missing <code class="docutils literal notranslate">:</code> and values in dictionary literals:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> values = {

... x: 1,

... y: 2,

... z:

... }

File "<stdin>", line 4

z:

^

SyntaxError: expression expected after dictionary key and ':'

>>> values = {x:1, y:2, z w:3}

File "<stdin>", line 1

values = {x:1, y:2, z w:3}

^

SyntaxError: ':' expected after dictionary key

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43823">bpo-43823</a>.)

</div></blockquote>

</li>

<li><code class="docutils literal notranslate">try</code> blocks without <code class="docutils literal notranslate">except</code> or <code class="docutils literal notranslate">finally</code> blocks:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> try:

... x = 2

... something = 3

File "<stdin>", line 3

something = 3

^^^^^^^^^

SyntaxError: expected 'except' or 'finally' block

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=44305">bpo-44305</a>.)

</div></blockquote>

</li>

<li>Usage of <code class="docutils literal notranslate">=</code> instead of <code class="docutils literal notranslate">==</code> in comparisons:

File "<stdin>", line 1

if rocket.position = event_horizon:

^

SyntaxError: cannot assign to attribute here. Maybe you meant '==' instead of '='?

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43797">bpo-43797</a>.)

</div></blockquote>

</li>

<li>Usage of <code class="docutils literal notranslate">*</code> in f-strings:

<div><div class="highlight-python notranslate"><div class="highlight"><pre>>>> f"Black holes {*all_black_holes} and revelations"

File "<stdin>", line 1

(*all_black_holes)

^

SyntaxError: f-string: cannot use starred expression here

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=41064">bpo-41064</a>.)

</div></blockquote>

</li>

</ul>

</section>

<h4>IndentationErrors<a class="headerlink" href="#indentationerrors" title="Permalink to this heading">¶</a></h4>

Many <a class="reference internal" href="../library/exceptions.html#IndentationError" title="IndentationError"><code class="xref py py-exc docutils literal notranslate">IndentationError</code></a> exceptions now have more context regarding what kind of block

was expecting an indentation, including the location of the statement:

<div class="highlight-python notranslate"><div class="highlight"><pre>>>> def foo():

... if lel:

... x = 2

File "<stdin>", line 3

x = 2

^

IndentationError: expected an indented block after 'if' statement in line 2

</pre></div>

</div>

</section>

<h4>AttributeErrors<a class="headerlink" href="#attributeerrors" title="Permalink to this heading">¶</a></h4>

When printing <a class="reference internal" href="../library/exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>, <code class="xref c c-func docutils literal notranslate">PyErr_Display()</code> will offer

suggestions of similar attribute names in the object that the exception was

raised from:

<div class="highlight-python notranslate"><div class="highlight"><pre>>>> collections.namedtoplo

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

AttributeError: module 'collections' has no attribute 'namedtoplo'. Did you mean: namedtuple?

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=38530">bpo-38530</a>.)

Uyarı

Notice this won’t work if <code class="xref c c-func docutils literal notranslate">PyErr_Display()</code> is not called to display the error

which can happen if some other custom error display function is used. This is a common

scenario in some REPLs like IPython.

</div>

</div></blockquote>

</section>

<h4>NameErrors<a class="headerlink" href="#nameerrors" title="Permalink to this heading">¶</a></h4>

When printing <a class="reference internal" href="../library/exceptions.html#NameError" title="NameError"><code class="xref py py-exc docutils literal notranslate">NameError</code></a> raised by the interpreter, <code class="xref c c-func docutils literal notranslate">PyErr_Display()</code>

will offer suggestions of similar variable names in the function that the exception

was raised from:

<div class="highlight-python notranslate"><div class="highlight"><pre>>>> schwarzschild_black_hole = None

>>> schwarschild_black_hole

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

NameError: name 'schwarschild_black_hole' is not defined. Did you mean: schwarzschild_black_hole?

</pre></div>

</div>

(Contributed by Pablo Galindo in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=38530">bpo-38530</a>.)

Uyarı

Notice this won’t work if <code class="xref c c-func docutils literal notranslate">PyErr_Display()</code> is not called to display the error,

which can happen if some other custom error display function is used. This is a common

scenario in some REPLs like IPython.

</div>

</div></blockquote>

</section>

<h3>PEP 626: Precise line numbers for debugging and other tools<a class="headerlink" href="#pep-626-precise-line-numbers-for-debugging-and-other-tools" title="Permalink to this heading">¶</a></h3>

PEP 626 brings more precise and reliable line numbers for debugging, profiling and coverage tools.

Tracing events, with the correct line number, are generated for all lines of code executed and only for lines of code that are executed.

The <code class="docutils literal notranslate">f_lineno</code> attribute of frame objects will always contain the expected line number.

The <code class="docutils literal notranslate">co_lnotab</code> attribute of code objects is deprecated and will be removed in 3.12.

Code that needs to convert from offset to line number should use the new <code class="docutils literal notranslate">co_lines()</code> method instead.

</section>

<h3>PEP 634: Structural Pattern Matching<a class="headerlink" href="#pep-634-structural-pattern-matching" title="Permalink to this heading">¶</a></h3>

Structural pattern matching has been added in the form of a match statement

and case statements of patterns with associated actions. Patterns

consist of sequences, mappings, primitive data types as well as class instances.

Pattern matching enables programs to extract information from complex data types,

branch on the structure of data, and apply specific actions based on different

forms of data.

<h4>Syntax and operations<a class="headerlink" href="#syntax-and-operations" title="Permalink to this heading">¶</a></h4>

The generic syntax of pattern matching is:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>match subject:

case <pattern_1>:

<action_1>

case <pattern_2>:

<action_2>

case <pattern_3>:

<action_3>

case _:

<action_wildcard>

</pre></div>

</div>

A match statement takes an expression and compares its value to successive

patterns given as one or more case blocks. Specifically, pattern matching

operates by:

<li>using data with type and shape (the <code class="docutils literal notranslate">subject</code>)</li>

<li>evaluating the <code class="docutils literal notranslate">subject</code> in the <code class="docutils literal notranslate">match</code> statement</li>

<li>comparing the subject with each pattern in a <code class="docutils literal notranslate">case</code> statement

from top to bottom until a match is confirmed.</li>

<li>executing the action associated with the pattern of the confirmed

match</li>

<li>If an exact match is not confirmed, the last case, a wildcard <code class="docutils literal notranslate">_</code>,

if provided, will be used as the matching case. If an exact match is

not confirmed and a wildcard case does not exist, the entire match

block is a no-op.</li>

</ol>

</div></blockquote>

</section>

<h4>Declarative approach<a class="headerlink" href="#declarative-approach" title="Permalink to this heading">¶</a></h4>

Readers may be aware of pattern matching through the simple example of matching

a subject (data object) to a literal (pattern) with the switch statement found

in C, Java or JavaScript (and many other languages). Often the switch statement

is used for comparison of an object/expression with case statements containing

literals.

More powerful examples of pattern matching can be found in languages such as

Scala and Elixir. With structural pattern matching, the approach is “declarative” and

explicitly states the conditions (the patterns) for data to match.

While an “imperative” series of instructions using nested “if” statements

could be used to accomplish something similar to structural pattern matching,

it is less clear than the “declarative” approach. Instead the “declarative”

approach states the conditions to meet for a match and is more readable through

its explicit patterns. While structural pattern matching can be used in its

simplest form comparing a variable to a literal in a case statement, its

true value for Python lies in its handling of the subject’s type and shape.

</section>

<h4>Simple pattern: match to a literal<a class="headerlink" href="#simple-pattern-match-to-a-literal" title="Permalink to this heading">¶</a></h4>

Let’s look at this example as pattern matching in its simplest form: a value,

the subject, being matched to several literals, the patterns. In the example

below, <code class="docutils literal notranslate">status</code> is the subject of the match statement. The patterns are

each of the case statements, where literals represent request status codes.

The associated action to the case is executed after a match:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>def http_error(status):

match status:

case 400:

return "Bad request"

case 404:

return "Not found"

case 418:

return "I'm a teapot"

case _:

return "Something's wrong with the internet"

</pre></div>

</div>

If the above function is passed a <code class="docutils literal notranslate">status</code> of 418, “I’m a teapot” is returned.

If the above function is passed a <code class="docutils literal notranslate">status</code> of 500, the case statement with

<code class="docutils literal notranslate">_</code> will match as a wildcard, and “Something’s wrong with the internet” is

returned.

Note the last block: the variable name, <code class="docutils literal notranslate">_</code>, acts as a wildcard and insures

the subject will always match. The use of <code class="docutils literal notranslate">_</code> is optional.

You can combine several literals in a single pattern using <code class="docutils literal notranslate">|</code> (“or”):

<div class="highlight-python3 notranslate"><div class="highlight"><pre>case 401 | 403 | 404:

return "Not allowed"

</pre></div>

</div>

<h5>Behavior without the wildcard<a class="headerlink" href="#behavior-without-the-wildcard" title="Permalink to this heading">¶</a></h5>

If we modify the above example by removing the last case block, the example

becomes:

match status:

case 400:

return "Bad request"

case 404:

return "Not found"

case 418:

return "I'm a teapot"

</pre></div>

</div>

Without the use of <code class="docutils literal notranslate">_</code> in a case statement, a match may not exist. If no

match exists, the behavior is a no-op. For example, if <code class="docutils literal notranslate">status</code> of 500 is

passed, a no-op occurs.

</section>

<h4>Patterns with a literal and variable<a class="headerlink" href="#patterns-with-a-literal-and-variable" title="Permalink to this heading">¶</a></h4>

Patterns can look like unpacking assignments, and a pattern may be used to bind

variables. In this example, a data point can be unpacked to its x-coordinate

and y-coordinate:

<div class="highlight-python3 notranslate"><div class="highlight"><pre># point is an (x, y) tuple

match point:

case (0, 0):

print("Origin")

case (0, y):

print(f"Y={y}")

case (x, 0):

case (x, y):

print(f"X={x}, Y={y}")

case _:

raise ValueError("Not a point")

</pre></div>

</div>

The first pattern has two literals, <code class="docutils literal notranslate">(0, 0)</code>, and may be thought of as an

extension of the literal pattern shown above. The next two patterns combine a

literal and a variable, and the variable binds a value from the subject

(<code class="docutils literal notranslate">point</code>). The fourth pattern captures two values, which makes it

conceptually similar to the unpacking assignment <code class="docutils literal notranslate">(x, y) = point</code>.

</section>

<h4>Patterns and classes<a class="headerlink" href="#patterns-and-classes" title="Permalink to this heading">¶</a></h4>

If you are using classes to structure your data, you can use as a pattern

the class name followed by an argument list resembling a constructor. This

pattern has the ability to capture class attributes into variables:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>class Point:

x: int

y: int

def location(point):

match point:

case Point(x=0, y=0):

print("Origin is the point's location.")

case Point(x=x, y=0):

print(f"X={x} and the point is on the x-axis.")

case Point():

print("The point is located somewhere else on the plane.")

case _:

print("Not a point")

</pre></div>

</div>

<h5>Patterns with positional parameters<a class="headerlink" href="#patterns-with-positional-parameters" title="Permalink to this heading">¶</a></h5>

You can use positional parameters with some builtin classes that provide an

ordering for their attributes (e.g. dataclasses). You can also define a specific

position for attributes in patterns by setting the <code class="docutils literal notranslate">__match_args__</code> special

attribute in your classes. If it’s set to (“x”, “y”), the following patterns

are all equivalent (and all bind the <code class="docutils literal notranslate">y</code> attribute to the <code class="docutils literal notranslate">var</code> variable):

<div class="highlight-python3 notranslate"><div class="highlight"><pre>Point(1, var)

Point(1, y=var)

Point(x=1, y=var)

Point(y=var, x=1)

</pre></div>

</div>

</section>

<h4>Nested patterns<a class="headerlink" href="#nested-patterns" title="Permalink to this heading">¶</a></h4>

Patterns can be arbitrarily nested. For example, if our data is a short

list of points, it could be matched like this:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>match points:

case []:

print("No points in the list.")

print("The origin is the only point in the list.")

case [Point(x, y)]:

print(f"A single point {x}, {y} is in the list.")

case [Point(0, y1), Point(0, y2)]:

print(f"Two points on the Y axis at {y1}, {y2} are in the list.")

case _:

print("Something else is found in the list.")

</pre></div>

</div>

</section>

<h4>Complex patterns and the wildcard<a class="headerlink" href="#complex-patterns-and-the-wildcard" title="Permalink to this heading">¶</a></h4>

To this point, the examples have used <code class="docutils literal notranslate">_</code> alone in the last case statement.

A wildcard can be used in more complex patterns, such as <code class="docutils literal notranslate">('error', code, _)</code>.

For example:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>match test_variable:

case ('warning', code, 40):

print("A warning has been received.")

case ('error', code, _):

print(f"An error {code} occurred.")

</pre></div>

</div>

In the above case, <code class="docutils literal notranslate">test_variable</code> will match for (‘error’, code, 100) and

(‘error’, code, 800).

</section>

<h4>Guard<a class="headerlink" href="#guard" title="Permalink to this heading">¶</a></h4>

We can add an <code class="docutils literal notranslate">if</code> clause to a pattern, known as a “guard”. If the

guard is false, <code class="docutils literal notranslate">match</code> goes on to try the next case block. Note

that value capture happens before the guard is evaluated:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>match point:

case Point(x, y) if x == y:

print(f"The point is located on the diagonal Y=X at {x}.")

case Point(x, y):

print(f"Point is not on the diagonal.")

</pre></div>

</div>

</section>

<h4>Other Key Features<a class="headerlink" href="#other-key-features" title="Permalink to this heading">¶</a></h4>

Several other key features:

<ul>

<li>Like unpacking assignments, tuple and list patterns have exactly the

same meaning and actually match arbitrary sequences. Technically,

the subject must be a sequence.

Therefore, an important exception is that patterns don’t match iterators.

Also, to prevent a common mistake, sequence patterns don’t match strings.</li>

<li>Sequence patterns support wildcards: <code class="docutils literal notranslate">[x, y, *rest]</code> and <code class="docutils literal notranslate">(x, y,

*rest)</code> work similar to wildcards in unpacking assignments. The

name after <code class="docutils literal notranslate">*</code> may also be <code class="docutils literal notranslate">_</code>, so <code class="docutils literal notranslate">(x, y, *_)</code> matches a sequence

of at least two items without binding the remaining items.</li>

<li>Mapping patterns: <code class="docutils literal notranslate">{"bandwidth": b, "latency": l}</code> captures the

<code class="docutils literal notranslate">"bandwidth"</code> and <code class="docutils literal notranslate">"latency"</code> values from a dict. Unlike sequence

patterns, extra keys are ignored. A wildcard <code class="docutils literal notranslate">**rest</code> is also

supported. (But <code class="docutils literal notranslate">**_</code> would be redundant, so is not allowed.)</li>

<li>Subpatterns may be captured using the <code class="docutils literal notranslate">as</code> keyword:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>case (Point(x1, y1), Point(x2, y2) as p2): ...

</pre></div>

</div>

This binds x1, y1, x2, y2 like you would expect without the <code class="docutils literal notranslate">as</code> clause,

and p2 to the entire second item of the subject.

</li>

<li>Most literals are compared by equality. However, the singletons <code class="docutils literal notranslate">True</code>,

<code class="docutils literal notranslate">False</code> and <code class="docutils literal notranslate">None</code> are compared by identity.</li>

<li>Named constants may be used in patterns. These named constants must be

dotted names to prevent the constant from being interpreted as a capture

variable:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>from enum import Enum

class Color(Enum):

RED = 0

GREEN = 1

BLUE = 2

match color:

case Color.RED:

print("I see red!")

case Color.GREEN:

print("Grass is green")

case Color.BLUE:

print("I'm feeling the blues :(")

</pre></div>

</div>

</li>

</ul>

For the full specification see <a class="pep reference external" href="https://peps.python.org/pep-0634/">PEP 634</a>. Motivation and rationale

are in <a class="pep reference external" href="https://peps.python.org/pep-0635/">PEP 635</a>, and a longer tutorial is in <a class="pep reference external" href="https://peps.python.org/pep-0636/">PEP 636</a>.

</section>

<h3>Optional <code class="docutils literal notranslate">EncodingWarning</code> and <code class="docutils literal notranslate">encoding="locale"</code> option<a class="headerlink" href="#optional-encodingwarning-and-encoding-locale-option" title="Permalink to this heading">¶</a></h3>

The default encoding of <code class="xref py py-class docutils literal notranslate">TextIOWrapper</code> and <a class="reference internal" href="../library/functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> is

platform and locale dependent. Since UTF-8 is used on most Unix

platforms, omitting <code class="docutils literal notranslate">encoding</code> option when opening UTF-8 files

(e.g. JSON, YAML, TOML, Markdown) is a very common bug. For example:

<div class="highlight-python3 notranslate"><div class="highlight"><pre># BUG: "rb" mode or encoding="utf-8" should be used.

with open("data.json") as f:

data = json.load(f)

</pre></div>

</div>

To find this type of bug, an optional <code class="docutils literal notranslate">EncodingWarning</code> is added.

It is emitted when <a class="reference internal" href="../library/sys.html#sys.flags" title="sys.flags"><code class="xref py py-data docutils literal notranslate">sys.flags.warn_default_encoding</code></a>

is true and locale-specific default encoding is used.

<code class="docutils literal notranslate">-X warn_default_encoding</code> option and <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONWARNDEFAULTENCODING"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNDEFAULTENCODING</code></a>

are added to enable the warning.

See <a class="reference internal" href="../library/io.html#io-text-encoding">Text Encoding</a> for more information.

</section>

<h2>New Features Related to Type Hints<a class="headerlink" href="#new-features-related-to-type-hints" title="Permalink to this heading">¶</a></h2>

This section covers major changes affecting <a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> type hints 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.

<h3>PEP 604: New Type Union Operator<a class="headerlink" href="#pep-604-new-type-union-operator" title="Permalink to this heading">¶</a></h3>

A new type union operator was introduced which enables the syntax <code class="docutils literal notranslate">X | Y</code>.

This provides a cleaner way of expressing ‘either type X or type Y’ instead of

using <a class="reference internal" href="../library/typing.html#typing.Union" title="typing.Union"><code class="xref py py-data docutils literal notranslate">typing.Union</code></a>, especially in type hints.

In previous versions of Python, to apply a type hint for functions accepting

arguments of multiple types, <a class="reference internal" href="../library/typing.html#typing.Union" title="typing.Union"><code class="xref py py-data docutils literal notranslate">typing.Union</code></a> was used:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>def square(number: Union[int, float]) -> Union[int, float]:

return number ** 2

</pre></div>

</div>

Type hints can now be written in a more succinct manner:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>def square(number: int | float) -> int | float:

return number ** 2

</pre></div>

</div>

This new syntax is also accepted as the second argument to <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>:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> isinstance(1, int | str)

True

</pre></div>

</div>

See <a class="reference internal" href="../library/stdtypes.html#types-union">Sendika Türü</a> and <a class="pep reference external" href="https://peps.python.org/pep-0604/">PEP 604</a> for more details.

(Contributed by Maggie Moss and Philippe Prados in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=41428">bpo-41428</a>,

with additions by Yurii Karabas and Serhiy Storchaka in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=44490">bpo-44490</a>.)

</section>

<h3>PEP 612: Parameter Specification Variables<a class="headerlink" href="#pep-612-parameter-specification-variables" title="Permalink to this heading">¶</a></h3>

Two new options to improve the information provided to static type checkers for

<a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a>‘s <code class="docutils literal notranslate">Callable</code> have been added to 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.

The first is the parameter specification variable. They are used to forward the

parameter types of one callable to another callable – a pattern commonly

found in higher order functions and decorators. Examples of usage can be found

in <a class="reference internal" href="../library/typing.html#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">typing.ParamSpec</code></a>. Previously, there was no easy way to type annotate

dependency of parameter types in such a precise manner.

The second option is the new <code class="docutils literal notranslate">Concatenate</code> operator. It’s used in conjunction

with parameter specification variables to type annotate a higher order callable

which adds or removes parameters of another callable. Examples of usage can

be found in <a class="reference internal" href="../library/typing.html#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-class docutils literal notranslate">typing.Concatenate</code></a>.

See <a class="reference internal" href="../library/typing.html#typing.Callable" title="typing.Callable"><code class="xref py py-class docutils literal notranslate">typing.Callable</code></a>, <a class="reference internal" href="../library/typing.html#typing.ParamSpec" title="typing.ParamSpec"><code class="xref py py-class docutils literal notranslate">typing.ParamSpec</code></a>,

<a class="reference internal" href="../library/typing.html#typing.Concatenate" title="typing.Concatenate"><code class="xref py py-class docutils literal notranslate">typing.Concatenate</code></a>, <a class="reference internal" href="../library/typing.html#typing.ParamSpecArgs" title="typing.ParamSpecArgs"><code class="xref py py-class docutils literal notranslate">typing.ParamSpecArgs</code></a>,

<a class="reference internal" href="../library/typing.html#typing.ParamSpecKwargs" title="typing.ParamSpecKwargs"><code class="xref py py-class docutils literal notranslate">typing.ParamSpecKwargs</code></a>, and <a class="pep reference external" href="https://peps.python.org/pep-0612/">PEP 612</a> for more details.

(Contributed by Ken Jin in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=41559">bpo-41559</a>, with minor enhancements by Jelle

Zijlstra in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43783">bpo-43783</a>. PEP written by Mark Mendoza.)

</section>

<h3>PEP 613: TypeAlias<a class="headerlink" href="#pep-613-typealias" title="Permalink to this heading">¶</a></h3>

<a class="pep reference external" href="https://peps.python.org/pep-0484/">PEP 484</a> introduced the concept of type aliases, only requiring them to be

top-level unannotated assignments. This simplicity sometimes made it difficult

for type checkers to distinguish between type aliases and ordinary assignments,

especially when forward references or invalid types were involved. Compare:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>StrCache = 'Cache[str]' # a type alias

LOG_PREFIX = 'LOG[DEBUG]' # a module constant

</pre></div>

</div>

Now 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 has a special value <code class="xref py py-data docutils literal notranslate">TypeAlias</code>

which lets you declare type aliases more explicitly:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>StrCache: TypeAlias = 'Cache[str]' # a type alias

LOG_PREFIX = 'LOG[DEBUG]' # a module constant

</pre></div>

</div>

See <a class="pep reference external" href="https://peps.python.org/pep-0613/">PEP 613</a> for more details.

(Contributed by Mikhail Golubev in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=41923">bpo-41923</a>.)

</section>

<h3>PEP 647: User-Defined Type Guards<a class="headerlink" href="#pep-647-user-defined-type-guards" title="Permalink to this heading">¶</a></h3>

<code class="xref py py-data docutils literal notranslate">TypeGuard</code> has been added to 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 to annotate

type guard functions and improve information provided to static type checkers

during type narrowing. For more information, please see <code class="xref py py-data docutils literal notranslate">TypeGuard</code>‘s

documentation, and <a class="pep reference external" href="https://peps.python.org/pep-0647/">PEP 647</a>.

(Contributed by Ken Jin and Guido van Rossum in <a class="reference external" href="https://bugs.python.org/issue?@action=redirect&bpo=43766">bpo-43766</a>.

PEP written by Eric Traut.)

</section>

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