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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Capsules — Python 3.6.7 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/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 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="Generator Objects" href="gen.html" /> <link rel="prev" title="Weak Reference Objects" href="weakref.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/c-api/capsule.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </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="gen.html" title="Generator Objects" accesskey="N">next</a> |</li> <li class="right" > <a href="weakref.html" title="Weak Reference 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">3.6.7 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="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"><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">New in version 3.1.</span></p> </div> <dl class="type"> <dt id="c.PyCapsule"> <code class="descname">PyCapsule</code><a class="headerlink" href="#c.PyCapsule" title="Permalink to this definition">¶</a></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 <code class="xref c c-type docutils literal notranslate"><span class="pre">void*</span></code> 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="c.PyCapsule_Destructor"> <code class="descname">PyCapsule_Destructor</code><a class="headerlink" href="#c.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 notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span> <span class="nf">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="#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="function"> <dt id="c.PyCapsule_CheckExact"> int <code class="descname">PyCapsule_CheckExact</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *p</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyCapsule_CheckExact" title="Permalink to this definition">¶</a></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>.</p> </dd></dl> <dl class="function"> <dt id="c.PyCapsule_New"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyCapsule_New</code><span class="sig-paren">(</span>void<em> *pointer</em>, const char<em> *name</em>, <a class="reference internal" href="#c.PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a><em> destructor</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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="#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 <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 <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="function"> <dt id="c.PyCapsule_GetPointer"> void* <code class="descname">PyCapsule_GetPointer</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em>, const char<em> *name</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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 <code class="xref c c-func docutils literal notranslate"><span class="pre">strcmp()</span></code> to compare capsule names.</p> </dd></dl> <dl class="function"> <dt id="c.PyCapsule_GetDestructor"> <a class="reference internal" href="#c.PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a> <code class="descname">PyCapsule_GetDestructor</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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="#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="function"> <dt id="c.PyCapsule_GetContext"> void* <code class="descname">PyCapsule_GetContext</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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="#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="function"> <dt id="c.PyCapsule_GetName"> const char* <code class="descname">PyCapsule_GetName</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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="#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="function"> <dt id="c.PyCapsule_Import"> void* <code class="descname">PyCapsule_Import</code><span class="sig-paren">(</span>const char<em> *name</em>, int<em> no_block</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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 <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. If <em>no_block</em> is true, import the module without blocking (using <a class="reference internal" href="import.html#c.PyImport_ImportModuleNoBlock" title="PyImport_ImportModuleNoBlock"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyImport_ImportModuleNoBlock()</span></code></a>). If <em>no_block</em> is false, import the module conventionally (using <a class="reference internal" href="import.html#c.PyImport_ImportModule" title="PyImport_ImportModule"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyImport_ImportModule()</span></code></a>).</p> <p>Return the capsule’s internal <em>pointer</em> on success. On failure, set an exception and return <em>NULL</em>.</p> </dd></dl> <dl class="function"> <dt id="c.PyCapsule_IsValid"> int <code class="descname">PyCapsule_IsValid</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em>, const char<em> *name</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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="#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-<em>NULL</em> 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="xref c c-func 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="function"> <dt id="c.PyCapsule_SetContext"> int <code class="descname">PyCapsule_SetContext</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em>, void<em> *context</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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 <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="function"> <dt id="c.PyCapsule_SetDestructor"> int <code class="descname">PyCapsule_SetDestructor</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em>, <a class="reference internal" href="#c.PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a><em> destructor</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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 <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="function"> <dt id="c.PyCapsule_SetName"> int <code class="descname">PyCapsule_SetName</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em>, const char<em> *name</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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 <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="function"> <dt id="c.PyCapsule_SetPointer"> int <code class="descname">PyCapsule_SetPointer</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *capsule</em>, void<em> *pointer</em><span class="sig-paren">)</span><a class="headerlink" href="#c.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 <code class="docutils literal notranslate"><span class="pre">0</span></code> on success. 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