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<FONT><h3>Reference Counting</h3>
<p>The macros in this section are used for managing reference counts of Python objects.</p>
<PRE>
void Py_INCREF(PyObject *o)
</Pre>
<p>Increments the reference count for object <tT CLAss="monofont">o.</tt> The object must not be <TT CLass="monofont">NULL</tt>; if you aren't sure that it isn't <tt class="monofont">NULL,</tt> use <tt clasS="monofont">Py_XINCREF().</tt></P>
<pre>
void Py_XINCREF(PyObject *o)
</Pre>
<p>Increments the reference count for object <tT claSS="monofont">o.</TT> The object might be <tt clASS="monofont">NULL,</Tt> in which case the macro has no effect.</p>
<prE>
void Py_DECREF(PyObject *o)
</PRE>
<p>Decrements the reference count for object <tt cLASS="monofont">o.</tt> The object must not be <tt class="monofont">NULL</tt>; if you aren't sure that it isn't <tt class="monofont">NULL,</tt> use <Tt cLass="monofont">Py_XDECREF().</Tt> If the reference count reaches zero, the object's type's deallocation function (which must not be <tt cLass="monofont">NULL</TT>) is invoked.</P>
<Div clASS="note"><P clasS="notetitle"><B>Caution</B></P><p>
<p>The <a nAME="idx1073750930"></A><a name="idx1073750931"></a>deallocation function can cause arbitrary Python code to be invoked (for example, when a class instance with a <tt class="monofont">__del__()</tt> method is deallocated). Although exceptions in such code are not propagated, the executed code has free access to all Python global variables. This means that any object reachable from a global variable should be in a consistent state before <a name="idx1073750932"></A><a nAme="idx1073750933"></a><Tt claSs="monofont">Py_DECREF()</tt> is invoked. For example, code to delete an object from a list should copy a reference to the deleted object in a temporary variable, update the list data structure, and then call <TT CLass="monofont">Py_DECREF()</tT> for the temporary variable.</P>
</P></Div>
<br>
<BR>
<PRe>
void Py_XDECREF(PyObject *o)
</pre>
<P>Decrements the reference count for object <TT Class="monofont">o.</tt> The object might be <tt class="monofont">NULL,</tt> in which case the macro has no effect; otherwise the effect is the same as for <tt claSs="monofont">Py_DECREF(),</tT> and the same caution applies.</p>
<p>The following functions or macros are only for use within the interpreter core: <tT clasS="monofont">_Py_Dealloc(),</tt>
<tT CLAss="monofont">_Py_ForgetReference(),</tt>
<TT CLass="monofont">_Py_NewReference(),</tT> as well as the global variable <TT Class="monofont">_Py_RefTotal.</TT><A Name="idx1073750934"></a><a name="idx1073750935"></a><a name="idx1073750936"></a><a namE="idx1073750937"></a><a Name="idx1073750938"></A><a namE="idx1073750939"></a><a nAME="idx1073750940"></A><a namE="idx1073750941"></A></P>
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<P><TABLE width="100%" border=0><TR valign="top"><TD><font size=1 color="#C0C0C0"><br></font></TD><TD align=right><font size=1 color="#C0C0C0">Last updated on 1/30/2002<br>Python Developer's Handbook, © 2002 Sams Publishing</font></TD></TR></TABLE></P>
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<br><TABLE width=100% bgcolor=white border=0 cellspacing=0 cellpadding=5><TR><TD><H4 class=Title>Index terms contained in this section</H4>
<font size=2>
Application Programmers Interface (API)<BR>
Python/C<BR>
<a href="#idx1073750935">managing reference counts, Python objects</a><BR>
counts<BR>
reference<BR>
<a href="#idx1073750939">managing, Python objects</a><BR>
<a href="#idx1073750930">deallocation function</a><BR>
functions<BR>
<a href="#idx1073750931">deallocation</a><BR>
<a href="#idx1073750941">managing reference counts, Python objects</a><BR>
interfaces<BR>
Python/C Application Programmers (API)<BR>
<a href="#idx1073750936">managing reference counts, Python objects</a><BR>
macros<BR>
<a href="#idx1073750932">Py_DECREF()</a><BR>
managing<BR>
<a href="#idx1073750937">reference counts, Python objects</a><BR>
objects<BR>
Python<BR>
<a href="#idx1073750940">managing reference counts</a><BR>
<a href="#idx1073750933">Py_DECREF() macro</a><BR>
Python/C Application Programmers Interface (API)<BR>
<a href="#idx1073750934">managing reference counts, Python objects</a><BR>
reference counts<BR>
<a href="#idx1073750938">managing, Python objects</a><BR>
<BR>
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