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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>Weak Reference Objects — Python 2.7.18 documentation</title> <link rel="stylesheet" href="../_static/classic.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/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 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="Capsules" href="capsule.html" /> <link rel="prev" title="Slice Objects" href="slice.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/c-api/weakref.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/c-api/weakref.html"> Python documentation for the Python3 version packaged in this release</a>. </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" 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="capsule.html" title="Capsules" accesskey="N">next</a> |</li> <li class="right" > <a href="slice.html" title="Slice 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">Python 2.7.18 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> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="weak-reference-objects"> <span id="weakrefobjects"></span><h1>Weak Reference Objects<a class="headerlink" href="#weak-reference-objects" title="Permalink to this headline">¶</a></h1> <p>Python supports <em>weak references</em> as first-class objects. There are two specific object types which directly implement weak references. The first is a simple reference object, and the second acts as a proxy for the original object as much as it can.</p> <dl class="function"> <dt id="c.PyWeakref_Check"> int <code class="descname">PyWeakref_Check</code><span class="sig-paren">(</span>ob<span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_Check" title="Permalink to this definition">¶</a></dt> <dd><p>Return true if <em>ob</em> is either a reference or proxy object.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyWeakref_CheckRef"> int <code class="descname">PyWeakref_CheckRef</code><span class="sig-paren">(</span>ob<span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_CheckRef" title="Permalink to this definition">¶</a></dt> <dd><p>Return true if <em>ob</em> is a reference object.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyWeakref_CheckProxy"> int <code class="descname">PyWeakref_CheckProxy</code><span class="sig-paren">(</span>ob<span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_CheckProxy" title="Permalink to this definition">¶</a></dt> <dd><p>Return true if <em>ob</em> is a proxy object.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyWeakref_NewRef"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyWeakref_NewRef</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ob</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *callback</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_NewRef" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: New reference.</em><p>Return a weak reference object for the object <em>ob</em>. This will always return a new reference, but is not guaranteed to create a new object; an existing reference object may be returned. The second parameter, <em>callback</em>, can be a callable object that receives notification when <em>ob</em> is garbage collected; it should accept a single parameter, which will be the weak reference object itself. <em>callback</em> may also be <code class="docutils literal notranslate"><span class="pre">None</span></code> or <em>NULL</em>. If <em>ob</em> is not a weakly-referencable object, or if <em>callback</em> is not callable, <code class="docutils literal notranslate"><span class="pre">None</span></code>, or <em>NULL</em>, this will return <em>NULL</em> and raise <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyWeakref_NewProxy"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyWeakref_NewProxy</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ob</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *callback</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_NewProxy" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: New reference.</em><p>Return a weak reference proxy object for the object <em>ob</em>. This will always return a new reference, but is not guaranteed to create a new object; an existing proxy object may be returned. The second parameter, <em>callback</em>, can be a callable object that receives notification when <em>ob</em> is garbage collected; it should accept a single parameter, which will be the weak reference object itself. <em>callback</em> may also be <code class="docutils literal notranslate"><span class="pre">None</span></code> or <em>NULL</em>. If <em>ob</em> is not a weakly-referencable object, or if <em>callback</em> is not callable, <code class="docutils literal notranslate"><span class="pre">None</span></code>, or <em>NULL</em>, this will return <em>NULL</em> and raise <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyWeakref_GetObject"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyWeakref_GetObject</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ref</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_GetObject" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: Borrowed reference.</em><p>Return the referenced object from a weak reference, <em>ref</em>. If the referent is no longer live, returns <code class="xref py py-const docutils literal notranslate"><span class="pre">Py_None</span></code>.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">This function returns a <strong>borrowed reference</strong> to the referenced object. This means that you should always call <a class="reference internal" href="refcounting.html#c.Py_INCREF" title="Py_INCREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_INCREF()</span></code></a> on the object except if you know that it cannot be destroyed while you are still using it.</p> </div> </dd></dl> <dl class="function"> <dt id="c.PyWeakref_GET_OBJECT"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyWeakref_GET_OBJECT</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *ref</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_GET_OBJECT" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: Borrowed reference.</em><p>Similar to <a class="reference internal" href="#c.PyWeakref_GetObject" title="PyWeakref_GetObject"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyWeakref_GetObject()</span></code></a>, but implemented as a macro that does no error checking.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.2.</span></p> </div> </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="slice.html" title="previous chapter">Slice Objects</a></p> <h4>Next topic</h4> <p class="topless"><a href="capsule.html" title="next chapter">Capsules</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/c-api/weakref.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input 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> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </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="capsule.html" title="Capsules" >next</a> |</li> <li class="right" > <a href="slice.html" title="Slice 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">Python 2.7.18 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> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2024, 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 December 09, 2024. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.8.5. </div> </body> </html>