<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="utf-8" />
<title>Context Variables Objects — Python 3.7.10 documentation</title>
<link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" />
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
<script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script>
<script type="text/javascript" src="../_static/jquery.js"></script>
<script type="text/javascript" src="../_static/underscore.js"></script>
<script type="text/javascript" src="../_static/doctools.js"></script>
<script type="text/javascript" src="../_static/language_data.js"></script>
<script type="text/javascript" src="../_static/sidebar.js"></script>
<link rel="search" type="application/opensearchdescription+xml"
title="Search within Python 3.7.10 documentation"
href="../_static/opensearch.xml"/>
<link rel="author" title="About these documents" href="../about.html" />
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="copyright" title="Copyright" href="../copyright.html" />
<link rel="next" title="DateTime Objects" href="datetime.html" />
<link rel="prev" title="Coroutine Objects" href="coro.html" />
<link rel="shortcut icon" type="image/png" href="../_static/py.png" />
<link rel="canonical" href="https://docs.python.org/3/c-api/contextvars.html" />
<script type="text/javascript" src="../_static/copybutton.js"></script>
<style>
@media only screen {
table.full-width-table {
width: 100%;
}
}
</style>
</head><body>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="datetime.html" title="DateTime Objects"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="coro.html" title="Coroutine Objects"
accesskey="P">previous</a> |</li>
<li><img src="../_static/py.png" alt=""
style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<a href="../index.html">3.7.10 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li>
<li class="nav-item nav-item-2"><a href="concrete.html" accesskey="U">Concrete Objects Layer</a> »</li>
<li class="right">
<div class="inline-search" style="display: none" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('.inline-search').show(0);</script>
|
</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<div class="section" id="context-variables-objects">
<span id="contextvarsobjects"></span><h1>Context Variables Objects<a class="headerlink" href="#context-variables-objects" title="Permalink to this headline">¶</a></h1>
<div class="versionchanged" id="contextvarsobjects-pointertype-change">
<div class="admonition note">
<p class="admonition-title">Note</p>
<span class="versionmodified changed">Changed in version 3.7.1: </span><p>In Python 3.7.1 the signatures of all context variables
C APIs were <strong>changed</strong> to use <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> pointers instead
of <a class="reference internal" href="#c.PyContext" title="PyContext"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContext</span></code></a>, <a class="reference internal" href="#c.PyContextVar" title="PyContextVar"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContextVar</span></code></a>, and
<a class="reference internal" href="#c.PyContextToken" title="PyContextToken"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyContextToken</span></code></a>, e.g.:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="c1">// in 3.7.0:</span>
<span class="n">PyContext</span> <span class="o">*</span><span class="nf">PyContext_New</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
<span class="c1">// in 3.7.1+:</span>
<span class="n">PyObject</span> <span class="o">*</span><span class="nf">PyContext_New</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
</pre></div>
</div>
<p>See <a class="reference external" href="https://bugs.python.org/issue34762">bpo-34762</a> for more details.</p>
</div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
<p>This section details the public C API for the <a class="reference internal" href="../library/contextvars.html#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> module.</p>
<dl class="type">
<dt id="c.PyContext">
<code class="sig-name descname">PyContext</code><a class="headerlink" href="#c.PyContext" title="Permalink to this definition">¶</a></dt>
<dd><p>The C structure used to represent a <a class="reference internal" href="../library/contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Context</span></code></a>
object.</p>
</dd></dl>
<dl class="type">
<dt id="c.PyContextVar">
<code class="sig-name descname">PyContextVar</code><a class="headerlink" href="#c.PyContextVar" title="Permalink to this definition">¶</a></dt>
<dd><p>The C structure used to represent a <a class="reference internal" href="../library/contextvars.html#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.ContextVar</span></code></a>
object.</p>
</dd></dl>
<dl class="type">
<dt id="c.PyContextToken">
<code class="sig-name descname">PyContextToken</code><a class="headerlink" href="#c.PyContextToken" title="Permalink to this definition">¶</a></dt>
<dd><p>The C structure used to represent a <code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Token</span></code> object.</p>
</dd></dl>
<dl class="var">
<dt id="c.PyContext_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContext_Type</code><a class="headerlink" href="#c.PyContext_Type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type object representing the <em>context</em> type.</p>
</dd></dl>
<dl class="var">
<dt id="c.PyContextVar_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContextVar_Type</code><a class="headerlink" href="#c.PyContextVar_Type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type object representing the <em>context variable</em> type.</p>
</dd></dl>
<dl class="var">
<dt id="c.PyContextToken_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject">PyTypeObject</a> <code class="sig-name descname">PyContextToken_Type</code><a class="headerlink" href="#c.PyContextToken_Type" title="Permalink to this definition">¶</a></dt>
<dd><p>The type object representing the <em>context variable token</em> type.</p>
</dd></dl>
<p>Type-check macros:</p>
<dl class="function">
<dt id="c.PyContext_CheckExact">
int <code class="sig-name descname">PyContext_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>o</em> is of type <a class="reference internal" href="#c.PyContext_Type" title="PyContext_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContext_Type</span></code></a>. <em>o</em> must not be
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>. This function always succeeds.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContextVar_CheckExact">
int <code class="sig-name descname">PyContextVar_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>o</em> is of type <a class="reference internal" href="#c.PyContextVar_Type" title="PyContextVar_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContextVar_Type</span></code></a>. <em>o</em> must not be
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>. This function always succeeds.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContextToken_CheckExact">
int <code class="sig-name descname">PyContextToken_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextToken_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>o</em> is of type <a class="reference internal" href="#c.PyContextToken_Type" title="PyContextToken_Type"><code class="xref c c-data docutils literal notranslate"><span class="pre">PyContextToken_Type</span></code></a>.
<em>o</em> must not be <code class="docutils literal notranslate"><span class="pre">NULL</span></code>. This function always succeeds.</p>
</dd></dl>
<p>Context object management functions:</p>
<dl class="function">
<dt id="c.PyContext_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_New</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a new empty context object. Returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error
has occurred.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContext_Copy">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_Copy</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Copy" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a shallow copy of the passed <em>ctx</em> context object.
Returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error has occurred.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContext_CopyCurrent">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContext_CopyCurrent</code><span class="sig-paren">(</span>void<span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CopyCurrent" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a shallow copy of the current thread context.
Returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error has occurred.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContext_Enter">
int <code class="sig-name descname">PyContext_Enter</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Enter" title="Permalink to this definition">¶</a></dt>
<dd><p>Set <em>ctx</em> as the current context for the current thread.
Returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success, and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContext_Exit">
int <code class="sig-name descname">PyContext_Exit</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ctx</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Exit" title="Permalink to this definition">¶</a></dt>
<dd><p>Deactivate the <em>ctx</em> context and restore the previous context as the
current context for the current thread. Returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success,
and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContext_ClearFreeList">
int <code class="sig-name descname">PyContext_ClearFreeList</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_ClearFreeList" title="Permalink to this definition">¶</a></dt>
<dd><p>Clear the context variable free list. Return the total number of
freed items. This function always succeeds.</p>
</dd></dl>
<p>Context variable functions:</p>
<dl class="function">
<dt id="c.PyContextVar_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContextVar_New</code><span class="sig-paren">(</span>const char<em> *name</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *def</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a new <code class="docutils literal notranslate"><span class="pre">ContextVar</span></code> object. The <em>name</em> parameter is used
for introspection and debug purposes. The <em>def</em> parameter may optionally
specify the default value for the context variable. If an error has
occurred, this function returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContextVar_Get">
int <code class="sig-name descname">PyContextVar_Get</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *default_value</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> **value</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Get" title="Permalink to this definition">¶</a></dt>
<dd><p>Get the value of a context variable. Returns <code class="docutils literal notranslate"><span class="pre">-1</span></code> if an error has
occurred during lookup, and <code class="docutils literal notranslate"><span class="pre">0</span></code> if no error occurred, whether or not
a value was found.</p>
<p>If the context variable was found, <em>value</em> will be a pointer to it.
If the context variable was <em>not</em> found, <em>value</em> will point to:</p>
<ul class="simple">
<li><p><em>default_value</em>, if not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>;</p></li>
<li><p>the default value of <em>var</em>, if not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>;</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">NULL</span></code></p></li>
</ul>
<p>If the value was found, the function will create a new reference to it.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContextVar_Set">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a> *<code class="sig-name descname">PyContextVar_Set</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Set" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Set the value of <em>var</em> to <em>value</em> in the current context. Returns a
pointer to a <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyObject</span></code></a> object, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error
has occurred.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyContextVar_Reset">
int <code class="sig-name descname">PyContextVar_Reset</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *var</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *token</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Reset" title="Permalink to this definition">¶</a></dt>
<dd><p>Reset the state of the <em>var</em> context variable to that it was in before
<a class="reference internal" href="#c.PyContextVar_Set" title="PyContextVar_Set"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyContextVar_Set()</span></code></a> that returned the <em>token</em> was called.
This function returns <code class="docutils literal notranslate"><span class="pre">0</span></code> on success and <code class="docutils literal notranslate"><span class="pre">-1</span></code> on error.</p>
</dd></dl>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h4>Previous topic</h4>
<p class="topless"><a href="coro.html"
title="previous chapter">Coroutine Objects</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="datetime.html"
title="next chapter">DateTime Objects</a></p>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">Report a Bug</a></li>
<li>
<a href="https://github.com/python/cpython/blob/3.7/Doc/c-api/contextvars.rst"
rel="nofollow">Show Source
</a>
</li>
</ul>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
>index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="datetime.html" title="DateTime Objects"
>next</a> |</li>
<li class="right" >
<a href="coro.html" title="Coroutine Objects"
>previous</a> |</li>
<li><img src="../_static/py.png" alt=""
style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<a href="../index.html">3.7.10 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li>
<li class="nav-item nav-item-2"><a href="concrete.html" >Concrete Objects Layer</a> »</li>
<li class="right">
<div class="inline-search" style="display: none" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('.inline-search').show(0);</script>
|
</li>
</ul>
</div>
<div class="footer">
© <a href="../copyright.html">Copyright</a> 2001-2021, Python Software Foundation.
<br />
The Python Software Foundation is a non-profit corporation.
<a href="https://www.python.org/psf/donations/">Please donate.</a>
<br />
Last updated on Feb 26, 2021.
<a href="../bugs.html">Found a bug</a>?
<br />
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.3.1.
</div>
</body>
</html>
