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<section id="capsules">
<span id="id1"></span><h1>Capsules<a class="headerlink" href="#capsules" title="Link to this heading">¶</a></h1>
<p id="index-0">Refer to <a class="reference internal" href="../extending/extending.html#using-capsules"><span class="std std-ref">Providing a C API for an Extension Module</span></a> for more information on using these objects.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.1.</span></p>
</div>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyCapsule">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule</span></span></span><a class="headerlink" href="#c.PyCapsule" title="Link to this definition">¶</a><br /></dt>
<dd><p>This subtype of <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> represents an opaque value, useful for C
extension modules who need to pass an opaque value (as a <span class="c-expr sig sig-inline c"><span class="kt">void</span><span class="p">*</span></span>
pointer) through Python code to other C code. It is often used to make a C
function pointer defined in one module available to other modules, so the
regular import mechanism can be used to access C APIs defined in dynamically
loaded modules.</p>
</dd></dl>
<dl class="c type">
<dt class="sig sig-object c" id="c.PyCapsule_Destructor">
<span class="k"><span class="pre">type</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_Destructor</span></span></span><a class="headerlink" href="#c.PyCapsule_Destructor" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>The type of a destructor callback for a capsule. Defined as:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">PyCapsule_Destructor</span><span class="p">)(</span><span class="n">PyObject</span><span class="w"> </span><span class="o">*</span><span class="p">);</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="#c.PyCapsule_New" title="PyCapsule_New"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_New()</span></code></a> for the semantics of PyCapsule_Destructor
callbacks.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_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">PyCapsule_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">p</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_CheckExact" title="Link to this definition">¶</a><br /></dt>
<dd><p>Return true if its argument is a <a class="reference internal" href="#c.PyCapsule" title="PyCapsule"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCapsule</span></code></a>. This function always
succeeds.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_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">PyCapsule_New</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">pointer</span></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="#c.PyCapsule_Destructor" title="PyCapsule_Destructor"><span class="n"><span class="pre">PyCapsule_Destructor</span></span></a><span class="w"> </span><span class="n"><span class="pre">destructor</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_New" title="Link to this definition">¶</a><br /></dt>
<dd><em class="refcount return_new_ref">Return value: New reference.</em><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Create a <a class="reference internal" href="#c.PyCapsule" title="PyCapsule"><code class="xref c c-type docutils literal notranslate"><span class="pre">PyCapsule</span></code></a> encapsulating the <em>pointer</em>. The <em>pointer</em>
argument may not be <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>On failure, set an exception and return <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>The <em>name</em> string may either be <code class="docutils literal notranslate"><span class="pre">NULL</span></code> or a pointer to a valid C string. If
non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>, this string must outlive the capsule. (Though it is permitted to
free it inside the <em>destructor</em>.)</p>
<p>If the <em>destructor</em> argument is not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, it will be called with the
capsule as its argument when it is destroyed.</p>
<p>If this capsule will be stored as an attribute of a module, the <em>name</em> should
be specified as <code class="docutils literal notranslate"><span class="pre">modulename.attributename</span></code>. This will enable other modules
to import the capsule using <a class="reference internal" href="#c.PyCapsule_Import" title="PyCapsule_Import"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_Import()</span></code></a>.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_GetPointer">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_GetPointer</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">capsule</span></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><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_GetPointer" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Retrieve the <em>pointer</em> stored in the capsule. On failure, set an exception
and return <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>The <em>name</em> parameter must compare exactly to the name stored in the capsule.
If the name stored in the capsule is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the <em>name</em> passed in must also
be <code class="docutils literal notranslate"><span class="pre">NULL</span></code>. Python uses the C function <code class="xref c c-func docutils literal notranslate"><span class="pre">strcmp()</span></code> to compare capsule
names.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_GetDestructor">
<a class="reference internal" href="#c.PyCapsule_Destructor" title="PyCapsule_Destructor"><span class="n"><span class="pre">PyCapsule_Destructor</span></span></a><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_GetDestructor</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">capsule</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_GetDestructor" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Return the current destructor stored in the capsule. On failure, set an
exception and return <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>It is legal for a capsule to have a <code class="docutils literal notranslate"><span class="pre">NULL</span></code> destructor. This makes a <code class="docutils literal notranslate"><span class="pre">NULL</span></code>
return code somewhat ambiguous; use <a class="reference internal" href="#c.PyCapsule_IsValid" title="PyCapsule_IsValid"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_IsValid()</span></code></a> or
<a class="reference internal" href="exceptions.html#c.PyErr_Occurred" title="PyErr_Occurred"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyErr_Occurred()</span></code></a> to disambiguate.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_GetContext">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_GetContext</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">capsule</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_GetContext" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Return the current context stored in the capsule. On failure, set an
exception and return <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>It is legal for a capsule to have a <code class="docutils literal notranslate"><span class="pre">NULL</span></code> context. This makes a <code class="docutils literal notranslate"><span class="pre">NULL</span></code>
return code somewhat ambiguous; use <a class="reference internal" href="#c.PyCapsule_IsValid" title="PyCapsule_IsValid"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_IsValid()</span></code></a> or
<a class="reference internal" href="exceptions.html#c.PyErr_Occurred" title="PyErr_Occurred"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyErr_Occurred()</span></code></a> to disambiguate.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_GetName">
<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="sig-name descname"><span class="n"><span class="pre">PyCapsule_GetName</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">capsule</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_GetName" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Return the current name stored in the capsule. On failure, set an exception
and return <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>It is legal for a capsule to have a <code class="docutils literal notranslate"><span class="pre">NULL</span></code> name. This makes a <code class="docutils literal notranslate"><span class="pre">NULL</span></code> return
code somewhat ambiguous; use <a class="reference internal" href="#c.PyCapsule_IsValid" title="PyCapsule_IsValid"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_IsValid()</span></code></a> or
<a class="reference internal" href="exceptions.html#c.PyErr_Occurred" title="PyErr_Occurred"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyErr_Occurred()</span></code></a> to disambiguate.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_Import">
<span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_Import</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>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">no_block</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_Import" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Import a pointer to a C object from a capsule attribute in a module. The
<em>name</em> parameter should specify the full name to the attribute, as in
<code class="docutils literal notranslate"><span class="pre">module.attribute</span></code>. The <em>name</em> stored in the capsule must match this
string exactly.</p>
<p>Return the capsule’s internal <em>pointer</em> on success. On failure, set an
exception and return <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.3: </span><em>no_block</em> has no effect anymore.</p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_IsValid">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_IsValid</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">capsule</span></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><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_IsValid" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Determines whether or not <em>capsule</em> is a valid capsule. A valid capsule is
non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>, passes <a class="reference internal" href="#c.PyCapsule_CheckExact" title="PyCapsule_CheckExact"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_CheckExact()</span></code></a>, has a non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> pointer
stored in it, and its internal name matches the <em>name</em> parameter. (See
<a class="reference internal" href="#c.PyCapsule_GetPointer" title="PyCapsule_GetPointer"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_GetPointer()</span></code></a> for information on how capsule names are
compared.)</p>
<p>In other words, if <a class="reference internal" href="#c.PyCapsule_IsValid" title="PyCapsule_IsValid"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyCapsule_IsValid()</span></code></a> returns a true value, calls to
any of the accessors (any function starting with <code class="docutils literal notranslate"><span class="pre">PyCapsule_Get</span></code>) are
guaranteed to succeed.</p>
<p>Return a nonzero value if the object is valid and matches the name passed in.
Return <code class="docutils literal notranslate"><span class="pre">0</span></code> otherwise. This function will not fail.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_SetContext">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_SetContext</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">capsule</span></span>, <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">context</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_SetContext" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Set the context pointer inside <em>capsule</em> to <em>context</em>.</p>
<p>Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_SetDestructor">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_SetDestructor</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">capsule</span></span>, <a class="reference internal" href="#c.PyCapsule_Destructor" title="PyCapsule_Destructor"><span class="n"><span class="pre">PyCapsule_Destructor</span></span></a><span class="w"> </span><span class="n"><span class="pre">destructor</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_SetDestructor" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Set the destructor inside <em>capsule</em> to <em>destructor</em>.</p>
<p>Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_SetName">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_SetName</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">capsule</span></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><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_SetName" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Set the name inside <em>capsule</em> to <em>name</em>. If non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>, the name must
outlive the capsule. If the previous <em>name</em> stored in the capsule was not
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>, no attempt is made to free it.</p>
<p>Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyCapsule_SetPointer">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyCapsule_SetPointer</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">capsule</span></span>, <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">pointer</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_SetPointer" title="Link to this definition">¶</a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Set the void pointer inside <em>capsule</em> to <em>pointer</em>. The pointer may not be
<code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
<p>Return <code class="docutils literal notranslate"><span class="pre">0</span></code> on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
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