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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="c function"> <dt class="sig sig-object c" id="c.PyWeakref_Check"> <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyWeakref_Check</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">ob</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_Check" title="Permalink to this definition">¶</a><br /></dt> <dd><p>Return true if <em>ob</em> is either a reference or proxy object. This function always succeeds.</p> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyWeakref_CheckRef"> <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyWeakref_CheckRef</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">ob</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_CheckRef" title="Permalink to this definition">¶</a><br /></dt> <dd><p>Return true if <em>ob</em> is a reference object. This function always succeeds.</p> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyWeakref_CheckProxy"> <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyWeakref_CheckProxy</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">ob</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_CheckProxy" title="Permalink to this definition">¶</a><br /></dt> <dd><p>Return true if <em>ob</em> is a proxy object. This function always succeeds.</p> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyWeakref_NewRef"> <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">PyWeakref_NewRef</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">ob</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">callback</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_NewRef" title="Permalink to this definition">¶</a><br /></dt> <dd><em class="refcount">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>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 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>. 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 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, this will return <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and raise <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyWeakref_NewProxy"> <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">PyWeakref_NewProxy</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">ob</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">callback</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_NewProxy" title="Permalink to this definition">¶</a><br /></dt> <dd><em class="refcount">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>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 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>. 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 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, this will return <code class="docutils literal notranslate"><span class="pre">NULL</span></code> and raise <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyWeakref_GetObject"> <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">PyWeakref_GetObject</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">ref</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_GetObject" title="Permalink to this definition">¶</a><br /></dt> <dd><em class="refcount">Return value: Borrowed 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>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="admonition note"> <p class="admonition-title">Note</p> <p>This function returns a <a class="reference internal" href="../glossary.html#term-borrowed-reference"><span class="xref std std-term">borrowed reference</span></a> 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 when it cannot be destroyed before the last usage of the borrowed reference.</p> </div> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyWeakref_GET_OBJECT"> <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">PyWeakref_GET_OBJECT</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">ref</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyWeakref_GET_OBJECT" title="Permalink to this definition">¶</a><br /></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> </dd></dl> <dl class="c function"> <dt class="sig sig-object c" id="c.PyObject_ClearWeakRefs"> <span class="kt"><span class="pre">void</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyObject_ClearWeakRefs</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">object</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyObject_ClearWeakRefs" title="Permalink 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>This function is called by the <a class="reference internal" href="typeobj.html#c.PyTypeObject.tp_dealloc" title="PyTypeObject.tp_dealloc"><code class="xref c c-member docutils literal notranslate"><span class="pre">tp_dealloc</span></code></a> handler to clear weak references.</p> <p>This iterates through the weak references for <em>object</em> and calls callbacks for those references which have one. It returns when all callbacks have been attempted.</p> </dd></dl> </section> <div class="clearer"></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="memoryview.html" title="previous chapter">MemoryView 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="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.10/Doc/c-api/weakref.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </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="memoryview.html" title="MemoryView objects" >previous</a> |</li> <li><img src="../_static/py.svg" alt="python logo" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.10.12 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> <li class="nav-item nav-item-this"><a href="">Weak Reference Objects</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="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> | </li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 2001-2025, Python Software Foundation. <br /> This page is licensed under the Python Software Foundation License Version 2. <br /> Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. <br /> See <a href="/license.html">History and License</a> for more information.<br /> <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> <br /> Last updated on February 04, 2025. <a href="/bugs.html">Found a bug</a>? <br /> Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 4.3.2. </div> </body> </html> Save