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<div class="section" id="capsules">
<span id="id1"></span><h1>Capsules<a class="headerlink" href="#capsules" title="Permalink to this headline">¶</a></h1>
<p id="index-0">Refer to <a class="reference internal" href="../extending/extending.html#using-capsules"><em>Providing a C API for an Extension Module</em></a> for more information on using these objects.</p>
<dl class="type">
<dt id="PyCapsule">
<tt class="descname">PyCapsule</tt><a class="headerlink" href="#PyCapsule" title="Permalink to this definition">¶</a></dt>
<dd><p>This subtype of <a class="reference internal" href="structures.html#PyObject" title="PyObject"><tt class="xref c c-type docutils literal"><span class="pre">PyObject</span></tt></a> represents an opaque value, useful for C
extension modules who need to pass an opaque value (as a <tt class="xref c c-type docutils literal"><span class="pre">void*</span></tt>
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="type">
<dt id="PyCapsule_Destructor">
<tt class="descname">PyCapsule_Destructor</tt><a class="headerlink" href="#PyCapsule_Destructor" title="Permalink to this definition">¶</a></dt>
<dd><p>The type of a destructor callback for a capsule. Defined as:</p>
<div class="highlight-c"><div class="highlight"><pre><span class="k">typedef</span> <span class="kt">void</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="o">*</span><span class="p">);</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="#PyCapsule_New" title="PyCapsule_New"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_New()</span></tt></a> for the semantics of PyCapsule_Destructor
callbacks.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_CheckExact">
int <tt class="descname">PyCapsule_CheckExact</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *p</em><big>)</big><a class="headerlink" href="#PyCapsule_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if its argument is a <a class="reference internal" href="#PyCapsule" title="PyCapsule"><tt class="xref c c-type docutils literal"><span class="pre">PyCapsule</span></tt></a>.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_New">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyCapsule_New</tt><big>(</big>void<em> *pointer</em>, const char<em> *name</em>, <a class="reference internal" href="#PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a><em> destructor</em><big>)</big><a class="headerlink" href="#PyCapsule_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a <a class="reference internal" href="#PyCapsule" title="PyCapsule"><tt class="xref c c-type docutils literal"><span class="pre">PyCapsule</span></tt></a> encapsulating the <em>pointer</em>. The <em>pointer</em>
argument may not be <em>NULL</em>.</p>
<p>On failure, set an exception and return <em>NULL</em>.</p>
<p>The <em>name</em> string may either be <em>NULL</em> or a pointer to a valid C string. If
non-<em>NULL</em>, 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 <em>NULL</em>, 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 <tt class="docutils literal"><span class="pre">modulename.attributename</span></tt>. This will enable other modules
to import the capsule using <a class="reference internal" href="#PyCapsule_Import" title="PyCapsule_Import"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_Import()</span></tt></a>.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_GetPointer">
void* <tt class="descname">PyCapsule_GetPointer</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em>, const char<em> *name</em><big>)</big><a class="headerlink" href="#PyCapsule_GetPointer" title="Permalink to this definition">¶</a></dt>
<dd><p>Retrieve the <em>pointer</em> stored in the capsule. On failure, set an exception
and return <em>NULL</em>.</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 <em>NULL</em>, the <em>name</em> passed in must also
be <em>NULL</em>. Python uses the C function <tt class="xref c c-func docutils literal"><span class="pre">strcmp()</span></tt> to compare capsule
names.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_GetDestructor">
<a class="reference internal" href="#PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a> <tt class="descname">PyCapsule_GetDestructor</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em><big>)</big><a class="headerlink" href="#PyCapsule_GetDestructor" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current destructor stored in the capsule. On failure, set an
exception and return <em>NULL</em>.</p>
<p>It is legal for a capsule to have a <em>NULL</em> destructor. This makes a <em>NULL</em>
return code somewhat ambiguous; use <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> or
<a class="reference internal" href="exceptions.html#PyErr_Occurred" title="PyErr_Occurred"><tt class="xref c c-func docutils literal"><span class="pre">PyErr_Occurred()</span></tt></a> to disambiguate.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_GetContext">
void* <tt class="descname">PyCapsule_GetContext</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em><big>)</big><a class="headerlink" href="#PyCapsule_GetContext" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current context stored in the capsule. On failure, set an
exception and return <em>NULL</em>.</p>
<p>It is legal for a capsule to have a <em>NULL</em> context. This makes a <em>NULL</em>
return code somewhat ambiguous; use <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> or
<a class="reference internal" href="exceptions.html#PyErr_Occurred" title="PyErr_Occurred"><tt class="xref c c-func docutils literal"><span class="pre">PyErr_Occurred()</span></tt></a> to disambiguate.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_GetName">
const char* <tt class="descname">PyCapsule_GetName</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em><big>)</big><a class="headerlink" href="#PyCapsule_GetName" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current name stored in the capsule. On failure, set an exception
and return <em>NULL</em>.</p>
<p>It is legal for a capsule to have a <em>NULL</em> name. This makes a <em>NULL</em> return
code somewhat ambiguous; use <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> or
<a class="reference internal" href="exceptions.html#PyErr_Occurred" title="PyErr_Occurred"><tt class="xref c c-func docutils literal"><span class="pre">PyErr_Occurred()</span></tt></a> to disambiguate.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_Import">
void* <tt class="descname">PyCapsule_Import</tt><big>(</big>const char<em> *name</em>, int<em> no_block</em><big>)</big><a class="headerlink" href="#PyCapsule_Import" title="Permalink to this definition">¶</a></dt>
<dd><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
<tt class="docutils literal"><span class="pre">module.attribute</span></tt>. The <em>name</em> stored in the capsule must match this
string exactly. If <em>no_block</em> is true, import the module without blocking
(using <a class="reference internal" href="import.html#PyImport_ImportModuleNoBlock" title="PyImport_ImportModuleNoBlock"><tt class="xref c c-func docutils literal"><span class="pre">PyImport_ImportModuleNoBlock()</span></tt></a>). If <em>no_block</em> is false,
import the module conventionally (using <a class="reference internal" href="import.html#PyImport_ImportModule" title="PyImport_ImportModule"><tt class="xref c c-func docutils literal"><span class="pre">PyImport_ImportModule()</span></tt></a>).</p>
<p>Return the capsule’s internal <em>pointer</em> on success. On failure, set an
exception and return <em>NULL</em>. However, if <a class="reference internal" href="#PyCapsule_Import" title="PyCapsule_Import"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_Import()</span></tt></a> failed to
import the module, and <em>no_block</em> was true, no exception is set.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_IsValid">
int <tt class="descname">PyCapsule_IsValid</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em>, const char<em> *name</em><big>)</big><a class="headerlink" href="#PyCapsule_IsValid" title="Permalink to this definition">¶</a></dt>
<dd><p>Determines whether or not <em>capsule</em> is a valid capsule. A valid capsule is
non-<em>NULL</em>, passes <a class="reference internal" href="#PyCapsule_CheckExact" title="PyCapsule_CheckExact"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_CheckExact()</span></tt></a>, has a non-<em>NULL</em> pointer
stored in it, and its internal name matches the <em>name</em> parameter. (See
<a class="reference internal" href="#PyCapsule_GetPointer" title="PyCapsule_GetPointer"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_GetPointer()</span></tt></a> for information on how capsule names are
compared.)</p>
<p>In other words, if <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> returns a true value, calls to
any of the accessors (any function starting with <tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_Get()</span></tt>) are
guaranteed to succeed.</p>
<p>Return a nonzero value if the object is valid and matches the name passed in.
Return 0 otherwise. This function will not fail.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_SetContext">
int <tt class="descname">PyCapsule_SetContext</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em>, void<em> *context</em><big>)</big><a class="headerlink" href="#PyCapsule_SetContext" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the context pointer inside <em>capsule</em> to <em>context</em>.</p>
<p>Return 0 on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_SetDestructor">
int <tt class="descname">PyCapsule_SetDestructor</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em>, <a class="reference internal" href="#PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a><em> destructor</em><big>)</big><a class="headerlink" href="#PyCapsule_SetDestructor" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the destructor inside <em>capsule</em> to <em>destructor</em>.</p>
<p>Return 0 on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_SetName">
int <tt class="descname">PyCapsule_SetName</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em>, const char<em> *name</em><big>)</big><a class="headerlink" href="#PyCapsule_SetName" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the name inside <em>capsule</em> to <em>name</em>. If non-<em>NULL</em>, the name must
outlive the capsule. If the previous <em>name</em> stored in the capsule was not
<em>NULL</em>, no attempt is made to free it.</p>
<p>Return 0 on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
<dl class="function">
<dt id="PyCapsule_SetPointer">
int <tt class="descname">PyCapsule_SetPointer</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em> *capsule</em>, void<em> *pointer</em><big>)</big><a class="headerlink" href="#PyCapsule_SetPointer" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the void pointer inside <em>capsule</em> to <em>pointer</em>. The pointer may not be
<em>NULL</em>.</p>
<p>Return 0 on success. Return nonzero and set an exception on failure.</p>
</dd></dl>
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