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  <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">
<p><span class="versionmodified changed">Changed in version 3.7.1: </span></p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<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="w"> </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="w"> </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/issue?&#64;action=redirect&amp;bpo=34762">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="c type">
<dt class="sig sig-object c" id="c.PyContext">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContext</span></span></span><a class="headerlink" href="#c.PyContext" title="Permalink to this definition">¶</a><br /></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="c type">
<dt class="sig sig-object c" id="c.PyContextVar">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar</span></span></span><a class="headerlink" href="#c.PyContextVar" title="Permalink to this definition">¶</a><br /></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="c type">
<dt class="sig sig-object c" id="c.PyContextToken">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextToken</span></span></span><a class="headerlink" href="#c.PyContextToken" title="Permalink to this definition">¶</a><br /></dt>
<dd><p>The C structure used to represent a <a class="reference internal" href="../library/contextvars.html#contextvars.Token" title="contextvars.Token"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Token</span></code></a> object.</p>
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyContext_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject"><span class="n"><span class="pre">PyTypeObject</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_Type</span></span></span><a class="headerlink" href="#c.PyContext_Type" title="Permalink to this definition">¶</a><br /></dt>
<dd><p>The type object representing the <em>context</em> type.</p>
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyContextVar_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject"><span class="n"><span class="pre">PyTypeObject</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar_Type</span></span></span><a class="headerlink" href="#c.PyContextVar_Type" title="Permalink to this definition">¶</a><br /></dt>
<dd><p>The type object representing the <em>context variable</em> type.</p>
</dd></dl>

<dl class="c var">
<dt class="sig sig-object c" id="c.PyContextToken_Type">
<a class="reference internal" href="type.html#c.PyTypeObject" title="PyTypeObject"><span class="n"><span class="pre">PyTypeObject</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextToken_Type</span></span></span><a class="headerlink" href="#c.PyContextToken_Type" title="Permalink to this definition">¶</a><br /></dt>
<dd><p>The type object representing the <em>context variable token</em> type.</p>
</dd></dl>

<p>Type-check macros:</p>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyContext_CheckExact">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_CheckExact</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">o</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CheckExact" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContextVar_CheckExact">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar_CheckExact</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">o</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_CheckExact" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContextToken_CheckExact">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextToken_CheckExact</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">o</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextToken_CheckExact" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContext_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_New</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_New" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContext_Copy">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_Copy</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ctx</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Copy" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContext_CopyCurrent">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_CopyCurrent</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_CopyCurrent" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContext_Enter">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_Enter</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ctx</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Enter" title="Permalink to this definition">¶</a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyContext_Exit">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContext_Exit</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ctx</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContext_Exit" title="Permalink to this definition">¶</a><br /></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>

<p>Context variable functions:</p>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyContextVar_New">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar_New</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">name</span></span>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">def</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_New" title="Permalink to this definition">¶</a><br /></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 specifies
a default value for the context variable, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> for no default.
If an error has occurred, this function returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyContextVar_Get">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar_Get</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">var</span></span>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">default_value</span></span>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">value</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Get" title="Permalink to this definition">¶</a><br /></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>Except for <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the function returns a new reference.</p>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyContextVar_Set">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar_Set</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">var</span></span>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">value</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Set" title="Permalink to this definition">¶</a><br /></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 new token object for this change, or <code class="docutils literal notranslate"><span class="pre">NULL</span></code> if an error has occurred.</p>
</dd></dl>

<dl class="c function">
<dt class="sig sig-object c" id="c.PyContextVar_Reset">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyContextVar_Reset</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">var</span></span>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">token</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyContextVar_Reset" title="Permalink to this definition">¶</a><br /></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>

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