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<h3>Error Handling</h3>
<p>Errors are indicated by returning <tT CLAss="monofont">NULL</tt> to the interpreter. Prior to returning <TT CLass="monofont">NULL</tT>, an exception should be set or cleared using one of the following functions:</P>
<PRe>
<b>void PyErr_Clear()</b> </pre>
<p>Clears any previously raised exceptions.</p>
<pre>
<b>PyObject *PyErr_Occurred()</b> </pre>
<p>Checks to see whether an error has been generated. If so, returns the current exception object. Otherwise, returns <tt cLasS="monofont">NULL</tt>.</p>
<Pre>
<b>void PyErr_NoMemory()</b> </Pre>
<p>Raises a <TT CLass="monofont">MemoryError</tT> exception.</P>
<PRe>
<b>void PyErr_SetFromErrno(PyObject *</b><b><I>exc</I></B><B>)</b> </pre>
<P>Raises an exception. <I><TT class="monofont">exc</tt></i>
is an exception object. The value of the exception is taken from the <tt class="monofont">errno</tt> variable in the C library.</p>
<prE>
<b>void PyErr_SetFromErrnoWithFilename(PyObject *</b><B><i>exc</i></b><B>, char *</b><b><i>filename</i></B><b>)</b> </pRE>
<P>Like <Tt claSS="monofont">PyErr_SetFromErrno()</TT> but includes the filename in the exception value as well.</p>
<pre>
<B>void PyErr_SetObject(PyObject *</B><B><I>exc</i></b><b>, PyObject *</b><B><I>val</I></B><b>)</b> </pre>
<p>Raises an exception. <i><tt class="monofont">exc</tt></i>
is an exception object and <i><tt ClaSs="monofont">val</tt></I>
is an object containing the value of the exception.</p>
<pre>
<B>void PyErr_SetString(PyObject *</b><b><i>exc</I></B><B>, char *</B><b><i>msg</i></b><B>)</B> </PRe>
<p>Raises an exception. <i><tT CLAss="monofont">exc</tt></I>
is an exception object and <I><TT class="monofont">msg</tt></i>
is a message describing what went wrong.</p>
<p>The <i><tt class="monofont">exc</tt></I>
argument in these functions can be set to one of the following:</p>
<p><TablE bordEr="1" ceLLSPacinG="0" CELlpadDING="1" widtH="100%">
<COLgroup span="2">
<tr>
<th valign="top">
<fOnt Size="2">
<P><b>C Name</b></p>
</fOnt></tH>
<TH ValigN="top">
<FONt sizE="2">
<P><B>Python Exception</B></p>
</fonT></TH>
</Tr>
<tr>
<td valign="top">
<font size="2">
<p><Tt cLass="monofont">PyExc_ArithmeticError</Tt></p>
</foNt></td>
<TD VAlign="top">
<FONT size="2">
<P><TT Class="monofont">ArithmeticError</TT></P>
</Font></td>
</tr>
<tr>
<td valign="top">
<fonT siZe="2">
<p><tT clasS="monofont">PyExc_AssertionError</tt></p>
</FONT></td>
<td VALIgn="top">
<foNT SIze="2">
<p><tT CLAss="monofont">AssertionError</tt></p>
</font></td>
</tr>
<tr>
<td valIgn="top">
<Font Size="2">
<p><Tt clASS="monofont">PyExc_AttributeError</Tt></p>
</foNT></TD>
<td vaLIGN="top">
<font SIZE="2">
<p><tt class="monofont">AttributeError</tt></p>
</font></td>
</tr>
<tR>
<td ValiGn="top">
<fonT sizE="2">
<P><TT clasS="monofont">PyExc_EnvironmentError</TT></P>
</font></TD>
<TD valiGN="top">
<FOnt size="2">
<p><tt class="monofont">EnvironmentError</tt></p>
</fonT></td>
</Tr>
<tr>
<Td valIgn="top">
<fONT Size="2">
<p><TT CLass="monofont">PyExc_EOFError</tT></P>
</FOnt></td>
<TD VAlign="top">
<font size="2">
<p><tt class="monofont">EOFError</Tt></p>
</Font></Td>
</tr>
<tR>
<td vALIGn="top">
<fonT SIZe="2">
<p><tt CLASs="monofont">PyExc_Exception</tt></p>
</FONT></td>
<td valign="top">
<font size="2">
<p><tT clAss="monofont">Exception</tT></p>
</fonT></td>
</tR>
<TR>
<Td valIGN="top">
<Font sIZE="2">
<P><tt clASS="monofont">PyExc_FloatingPointError</Tt></p>
</font></td>
<td valign="top">
<font SizE="2">
<p><tt Class="monofont">FloatingPointError</Tt></p>
</fONT></Td>
</tr>
<tR>
<TD ValigN="top">
<FONt sizE="2">
<P><TT class="monofont">PyExc_ImportError</tt></p>
</font></td>
<td valiGn="top">
<fOnt sIze="2">
<p><tT claSS="monofont">ImportError</TT></p>
</fonT></TD>
</Tr>
<tr>
<tD VALign="top">
<fONT Size="2">
<p><tt class="monofont">PyExc_IndexError</tt></p>
</font></td>
<Td vAligN="top">
<font Size="2">
<P><TT Class="monofont">IndexError</TT></P>
</Font></tD>
</TR>
<Tr>
<td vALIGn="top">
<font size="2">
<p><tt class="monofont">PyExc_IOError</tt></p>
</FonT></td>
<tD valiGn="top">
<foNT SIze="2">
<p><tT CLAss="monofont">IOError</tt></P>
</FONt></td>
</tR>
<TR>
<Td valign="top">
<font size="2">
<p><tt clAss="monofont">PyExc_KeyError</Tt></p>
</fOnt></td>
<Td vaLIGN="top">
<font SIZE="2">
<p><tt cLASS="monofont">KeyError</tt></p>
</fONT></Td>
</tr>
<tr>
<td valign="top">
<font sizE="2">
<p><tT claSs="monofont">PyExc_KeyboardInterrupt</tt></p>
</Font></TD>
<TD valiGN="top">
<FOnt siZE="2">
<P><Tt claSS="monofont">KeyboardInterrupt</TT></p>
</font></td>
</tr>
<tr>
<td valign="top">
<fOnt Size="2">
<P><tt clAss="monofont">PyExc_LookupError</tT></P>
</FOnt></td>
<TD VAlign="top">
<FONT size="2">
<P><TT Class="monofont">LookupError</tt></p>
</font></td>
</tr>
<tr>
<td vAliGn="top">
<foNt sizE="2">
<p><tt CLASs="monofont">PyExc_MemoryError</tt></p>
</FONT></td>
<td VALIgn="top">
<foNT SIze="2">
<p><tt class="monofont">MemoryError</tt></p>
</font></td>
</tR>
<tr>
<Td vaLign="top">
<fOnt sIZE="2">
<P><tt clASS="monofont">PyExc_NameError</Tt></p>
</foNT></TD>
<td vaLIGN="top">
<font size="2">
<p><tt class="monofont">NameError</tt></p>
</fOnt></Td>
</tr>
<Tr>
<td vAligN="top">
<FONt sizE="2">
<P><TT clasS="monofont">PyExc_NotImplementedError</TT></P>
</font></TD>
<TD valign="top">
<font size="2">
<p><tt claSs="monofont">NotImplementedError</tT></p>
</foNt></td>
</tR>
<tr>
<tD VALign="top">
<fONT Size="2">
<p><TT CLass="monofont">PyExc_OSError</tT></P>
</FOnt></td>
<td valign="top">
<font size="2">
<P><tt ClasS="monofont">OSError</tt></p>
</fOnt></tD>
</TR>
<Tr>
<td vALIGn="top">
<fonT SIZe="2">
<p><tt CLASs="monofont">PyExc_OverflowError</tt></p>
</font></td>
<td valign="top">
<foNt sIze="2">
<p><Tt claSs="monofont">OverflowError</tt></P>
</FONt></td>
</tR>
<TR>
<Td valIGN="top">
<Font sIZE="2">
<P><tt class="monofont">PyExc_RuntimeError</tt></p>
</font></td>
<td vaLigN="top">
<fonT size="2">
<P><tt cLASS="monofont">RuntimeError</tt></p>
</fONT></Td>
</tr>
<tR>
<TD ValigN="top">
<FONt size="2">
<p><tt class="monofont">PyExc_StandardError</tt></p>
</font></Td>
<tD valIgn="top">
<foNt siZE="2">
<P><Tt claSS="monofont">StandardError</TT></p>
</fonT></TD>
</Tr>
<tr>
<tD VALign="top">
<font size="2">
<p><tt class="monofont">PyExc_SyntaxError</tT></p>
</fOnt></tD>
<td vaLign="top">
<FONT size="2">
<P><TT Class="monofont">SyntaxError</TT></P>
</Font></tD>
</TR>
<Tr>
<td valign="top">
<font size="2">
<p><tt ClaSs="monofont">PyExc_SystemError</tt></P>
</font></Td>
<td VALIgn="top">
<foNT SIze="2">
<p><tT CLAss="monofont">SystemError</tt></P>
</FONt></td>
</tr>
<tr>
<td valign="top">
<font sIze="2">
<P><tt cLass="monofont">PyExc_SystemExit</tT></p>
</foNT></TD>
<td vaLIGN="top">
<font SIZE="2">
<p><tt cLASS="monofont">SystemExit</tt></p>
</font></td>
</tr>
<tr>
<td valigN="top">
<foNt siZe="2">
<p><tt ClasS="monofont">PyExc_TypeError</TT></P>
</font></TD>
<TD valiGN="top">
<FOnt siZE="2">
<P><Tt class="monofont">TypeError</tt></p>
</font></td>
</tr>
<tr>
<tD vaLign="top">
<Font sIze="2">
<p><TT CLass="monofont">PyExc_UnicodeError</tT></P>
</FOnt></td>
<TD VAlign="top">
<FONT size="2">
<p><tt class="monofont">UnicodeError</tt></p>
</font></tD>
</tr>
<Tr>
<td ValigN="top">
<fonT SIZe="2">
<p><tt CLASs="monofont">PyExc_ValueError</tt></p>
</FONT></td>
<td VALIgn="top">
<font size="2">
<p><tt class="monofont">ValueError</tt></P>
</foNt></td>
</Tr>
<tr>
<tD valIGN="top">
<Font sIZE="2">
<P><tt clASS="monofont">PyExc_ZeroDivisionError</Tt></p>
</foNT></TD>
<td valign="top">
<font size="2">
<p><tt cLasS="monofont">ZeroDivisionError</tt></p>
</Font></tD>
</tr>
</cOLGRoup>
</tABLE></p>
<p>The following example shows how an exception is typically set and an error returned in extension code:</p>
<pRE>
PyErr_SetString(PyExc_ValueError,"Expected a positive value!");
return NULL; </PRe>
<p>An extension module can define a new exception type by using the following function:</p>
<pRE>
<B>PyObject *PyErr_NewException(char *</B><b><i>excname</i></b><b>, PyObject *</b><b><i>base</i></b><b>, PyObject *</b><b><i>dict</i></b><b>)</b> </prE>
<p>Creates a new exception object. <i><Tt clAss="monofont">excname</tt></I>
is the name of the exception in the form <tt cLASS="monofont">"</tt><i><tT CLAss="monofont">modulename</tt></I>
<TT Class="monofont">.</TT><I><Tt class="monofont">excname</tt></i>
<tt class="monofont">"</tt>, <i><tT clAss="monofont">base</tT></i>
is an optional base class for the exception, and <i><tt ClasS="monofont">dict</TT></I>
is an optional dictionary used as the <tt clASS="monofont">_ _dict_ _</Tt> attribute of the resulting exception class. Both of these arguments are normally set to <tt cLASS="monofont">NULL</tt>. The returned object is a class object.</p>
<p>The following example shows how a new exception is created in an extension module:</P>
<PRE>
static PyObject *SpamError;
...
/* Module initialization function */
initspam(void) {
PyObject *m, *d;
m = Py_InitModule("spam",SpamMethods);
d = PyModule_GetDict(m);
SpamError = PyErr_NewException("spam.error", NULL, NULL);
PyDict_SetItemString(d,"error",SpamError);
...
} </pre>
</font>
<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 3/28/2002<br>Python Essential Reference, Second Edition, © 2002 New Riders Publishing</font></TD></TR></TABLE></P>
<TABLE border=0 width="100%" cellspacing=0 cellpadding=0><TR><td align=left width="15%" class="headingsubbarbg"><a href="126.html" title="Converting Data from C to Python"><font size="1">< BACK</font></a></td><td align=center width="70%" class="headingsubbarbg"><font size="1"><a href="popanote.asp?pubui=oreilly&bookname=0735710910&snode=127" target="_blank" title="Make a public or private annnotation">Make Note</a> | <a href="127.html" title="Use a Safari bookmark to remember this section">Bookmark</a></font></td><td align=right width="15%" class="headingsubbarbg"><a href="128.html" title="Reference Counting"><font size="1">CONTINUE ></font></a></td></TR></TABLE>
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