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  <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="PyWeakref_Check">
int <tt class="descname">PyWeakref_Check</tt><big>(</big>ob<big>)</big><a class="headerlink" href="#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>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

<dl class="function">
<dt id="PyWeakref_CheckRef">
int <tt class="descname">PyWeakref_CheckRef</tt><big>(</big>ob<big>)</big><a class="headerlink" href="#PyWeakref_CheckRef" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>ob</em> is a reference object.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

<dl class="function">
<dt id="PyWeakref_CheckProxy">
int <tt class="descname">PyWeakref_CheckProxy</tt><big>(</big>ob<big>)</big><a class="headerlink" href="#PyWeakref_CheckProxy" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if <em>ob</em> is a proxy object.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

<dl class="function">
<dt id="PyWeakref_NewRef">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyWeakref_NewRef</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*ob</em>, <a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*callback</em><big>)</big><a class="headerlink" href="#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 <tt class="docutils literal"><span class="pre">None</span></tt> or <em>NULL</em>.  If <em>ob</em> is not a
weakly-referencable object, or if <em>callback</em> is not callable, <tt class="docutils literal"><span class="pre">None</span></tt>, 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"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

<dl class="function">
<dt id="PyWeakref_NewProxy">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyWeakref_NewProxy</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*ob</em>, <a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*callback</em><big>)</big><a class="headerlink" href="#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 <tt class="docutils literal"><span class="pre">None</span></tt> or <em>NULL</em>.  If <em>ob</em>
is not a weakly-referencable object, or if <em>callback</em> is not callable,
<tt class="docutils literal"><span class="pre">None</span></tt>, 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"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

<dl class="function">
<dt id="PyWeakref_GetObject">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyWeakref_GetObject</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*ref</em><big>)</big><a class="headerlink" href="#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 <tt class="xref py py-const docutils literal"><span class="pre">Py_None</span></tt>.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
<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#Py_INCREF" title="Py_INCREF"><tt class="xref c c-func docutils literal"><span class="pre">Py_INCREF()</span></tt></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="PyWeakref_GET_OBJECT">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyWeakref_GET_OBJECT</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*ref</em><big>)</big><a class="headerlink" href="#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="#PyWeakref_GetObject" title="PyWeakref_GetObject"><tt class="xref c c-func docutils literal"><span class="pre">PyWeakref_GetObject()</span></tt></a>, but implemented as a macro that does no
error checking.</p>
<p class="versionadded">
<span class="versionmodified">New in version 2.2.</span></p>
</dd></dl>

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