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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>