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<div class="section" id="weak-reference-objects">
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<span id="weakrefobjects"></span><h1>Weak Reference Objects<a class="headerlink" href="#weak-reference-objects" title="Permalink to this headline">¶</a></h1>
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<p>Python supports <em>weak references</em> as first-class objects. There are two
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specific object types which directly implement weak references. The first is a
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simple reference object, and the second acts as a proxy for the original object
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as much as it can.</p>
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<dl class="function">
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<dt id="c.PyWeakref_Check">
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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>
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<dd><p>Return true if <em>ob</em> is either a reference or proxy object.</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.PyWeakref_CheckRef">
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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>
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<dd><p>Return true if <em>ob</em> is a reference object.</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.PyWeakref_CheckProxy">
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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>
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<dd><p>Return true if <em>ob</em> is a proxy object.</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.PyWeakref_NewRef">
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<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>
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<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
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a new reference, but is not guaranteed to create a new object; an existing
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reference object may be returned. The second parameter, <em>callback</em>, can be a
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callable object that receives notification when <em>ob</em> is garbage collected; it
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should accept a single parameter, which will be the weak reference object
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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
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weakly-referencable object, or if <em>callback</em> is not callable, <code class="docutils literal notranslate"><span class="pre">None</span></code>, or
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<em>NULL</em>, this will return <em>NULL</em> 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>
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</dd></dl>
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<dl class="function">
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<dt id="c.PyWeakref_NewProxy">
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<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>
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<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
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return a new reference, but is not guaranteed to create a new object; an
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existing proxy object may be returned. The second parameter, <em>callback</em>, can
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be a callable object that receives notification when <em>ob</em> is garbage
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collected; it should accept a single parameter, which will be the weak
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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>
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is not a weakly-referencable object, or if <em>callback</em> is not callable,
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<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#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.PyWeakref_GetObject">
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<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>
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<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
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no longer live, returns <code class="xref py py-const docutils literal notranslate"><span class="pre">Py_None</span></code>.</p>
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<div class="admonition note">
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<p class="admonition-title">Note</p>
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<p>This function returns a <strong>borrowed reference</strong> to the referenced object.
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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
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except if you know that it cannot be destroyed while you are still
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using it.</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.PyWeakref_GET_OBJECT">
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<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>
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<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
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