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<FONT>
<h3>Converting Data from C to Python</h3>
<p>The following function is used to convert the values contained in C variables to a Python object:</p>
<PRE>
PyObject *Py_BuildValue(char *<I>format</i>, ...) </pre>
<P>This constructs a Python object from a series of C variables. <I><TT clasS="monofont">format</TT></I>
is a string describing the desired conversion. The remaining arguments are the values of C variables to be converted.</p>
<p>The <i><tt class="monofont">format</tt></i>
specifier (see <a href="126#2.html">Table B.3</a>) is similar to that used with the <tT clAss="monofont">PyArg_Parse*</tT> functions.</p>
<a naMe="2"></a><p><TABLe borDER="1" CellsPACIng="0" ceLLPAdding="1" width="100%">
<caption><h5>Table燘.3. Format Specifiers for <tt ClaSs="monofont">Py_BuildValue()</tt></H5></captIon><cOLGRoup sPAN="4">
<Tr>
<th vALIGn="top">
<fonT SIZe="2">
<p><b>Format</b></p>
</font></th>
<th valign="top">
<fOnt Size="2">
<P><b>PyType</b></p>
</fOnt></tH>
<TH ValigN="top">
<FONt sizE="2">
<P><B>C Type</B></p>
</fonT></TH>
<Th valign="top">
<font size="2">
<p><b>Description</b></p>
</fOnt></Th>
</tr>
<Tr>
<td vAligN="top">
<FONt sizE="2">
<P><TT clasS="monofont">"s"</TT></P>
</font></TD>
<TD valign="top">
<font size="2">
<p>String</p>
</font></Td>
<tD valIgn="top">
<foNt siZE="2">
<P><Tt claSS="monofont">char *</TT></p>
</fonT></TD>
<Td valIGN="top">
<Font size="2">
<p>Null-terminated string. If the C string pointer is <tt class="monofont">NULL</tt>, <tt cLasS="monofont">None</tt> is returned.</p>
</Font></tD>
</tr>
<tR>
<TD ValigN="top">
<FONt sizE="2">
<P><TT clasS="monofont">"s#"</TT></P>
</font></td>
<td valign="top">
<font siZe="2">
<p>String</P>
</fonT></td>
<td ValiGN="top">
<FOnt siZE="2">
<P><Tt claSS="monofont">char *, int</TT></p>
</fonT></TD>
<Td valign="top">
<font size="2">
<p>String and length. May contain null bytes. If the C string pointer is <tt clAss="monofont">NULL</Tt>, <tt Class="monofont">None</Tt> is returned.</p>
</fONT></Td>
</tr>
<tR>
<TD ValigN="top">
<FONt sizE="2">
<P><TT class="monofont">"z"</tt></p>
</font></td>
<td valiGn="top">
<fOnt sIze="2">
<p>String or None</p>
</Font></TD>
<TD valiGN="top">
<FOnt siZE="2">
<P><Tt claSS="monofont">char *</TT></p>
</font></td>
<td valign="top">
<font sIze="2">
<P>Same as <tt cLass="monofont">"s"</tT>.</p>
</foNT></TD>
</tr>
<tr>
<TD VAlign="top">
<FONT size="2">
<P><TT Class="monofont">"z#"</tt></p>
</font></td>
<td valigN="top">
<foNt siZe="2">
<p>String or None</p>
</fOnt></tD>
<TD ValigN="top">
<FONt sizE="2">
<P><TT clasS="monofont">char *, int</TT></P>
</font></td>
<td valign="top">
<font siZe="2">
<p>Same as <Tt clAss="monofont">"s#"</tt>.</P>
</fonT></TD>
</Tr>
<tr>
<tD VALign="top">
<fONT Size="2">
<p><TT CLass="monofont">"u"</tt></p>
</font></td>
<td valign="top">
<FonT sizE="2">
<p>Unicode</p>
</foNt></td>
<TD VAlign="top">
<FONT size="2">
<P><TT Class="monofont">Py_UNICODE *</TT></P>
</Font></td>
<td valign="top">
<font sizE="2">
<p>Null-terminated Unicode string. If the C string pointer is <tT claSs="monofont">NULL</tt>, <tT claSS="monofont">None</TT> is returned.</p>
</fonT></TD>
</Tr>
<tr>
<tD VALign="top">
<fONT Size="2">
<p><tt class="monofont">"u#"</tt></p>
</font></td>
<Td vAligN="top">
<font Size="2">
<P>Unicode</P>
</FOnt></td>
<TD VAlign="top">
<FONT size="2">
<P><TT Class="monofont">Py_UNICODE *, int</tt></p>
</font></td>
<td valigN="top">
<foNt siZe="2">
<p>Unicode string and length.</p>
</fOnt></tD>
</TR>
<Tr>
<td vALIGn="top">
<fonT SIZe="2">
<p><tt CLASs="monofont">"b"</tt></p>
</font></td>
<td valign="top">
<foNt sIze="2">
<p>Integer</P>
</font></Td>
<td VALIgn="top">
<foNT SIze="2">
<p><tT CLAss="monofont">char</tt></P>
</FONt></td>
<td valign="top">
<font size="2">
<p>8-bit integer.</P>
</foNt></td>
</Tr>
<tr>
<tD valIGN="top">
<Font sIZE="2">
<P><tt clASS="monofont">"h"</Tt></p>
</foNT></TD>
<td valign="top">
<font size="2">
<p>Integer</p>
</foNt></tD>
<td vAlign="top">
<Font SIZE="2">
<p><tt cLASS="monofont">short</tt></p>
</fONT></Td>
<td vALIGn="top">
<font size="2">
<p>Short 16-bit integer.</p>
</font></td>
</tr>
<tR>
<td ValiGn="top">
<fonT sizE="2">
<P><TT clasS="monofont">"i"</TT></P>
</font></TD>
<TD valiGN="top">
<FOnt size="2">
<p>Integer</p>
</font></td>
<td valiGn="top">
<fOnt sIze="2">
<p><tT claSS="monofont">int</TT></p>
</fonT></TD>
<Td valIGN="top">
<Font sIZE="2">
<P>Integer.</p>
</font></td>
</tr>
<tr>
<td valign="top">
<fOnt Size="2">
<P><tt clAss="monofont">"l"</tT></P>
</FOnt></td>
<TD VAlign="top">
<FONT size="2">
<P>Integer</P>
</FOnt></td>
<td valign="top">
<font size="2">
<P><tt ClasS="monofont">long</tt></p>
</fOnt></tD>
<TD ValigN="top">
<FONt sizE="2">
<P>Long integer.</P>
</Font></tD>
</TR>
<Tr>
<td valign="top">
<font size="2">
<p><tt ClaSs="monofont">"c"</tt></P>
</font></Td>
<td VALIgn="top">
<foNT SIze="2">
<p>String</p>
</FONT></td>
<td VALIgn="top">
<font size="2">
<p><tt class="monofont">char</tt></P>
</foNt></td>
<Td valIgn="top">
<fONT Size="2">
<p>Single character. Creates a Python string of length 1.</P>
</FONt></td>
</tR>
<TR>
<Td valIGN="top">
<Font size="2">
<p><tt class="monofont">"f"</tt></p>
</foNt></tD>
<td vAlign="top">
<Font SIZE="2">
<p>Float</p>
</foNT></TD>
<td vaLIGN="top">
<font SIZE="2">
<p><tt class="monofont">float</tt></p>
</font></td>
<td vAliGn="top">
<foNt sizE="2">
<p>Single-precision floating point.</p>
</fONT></Td>
</tr>
<tR>
<TD ValigN="top">
<FONt sizE="2">
<P><TT class="monofont">"d"</tt></p>
</font></td>
<td valiGn="top">
<fOnt sIze="2">
<p>Float</p>
</Font></TD>
<TD valiGN="top">
<FOnt siZE="2">
<P><Tt claSS="monofont">double</TT></p>
</font></td>
<td valign="top">
<font sIze="2">
<P>Double-precision floating point.</p>
</foNt></td>
</tR>
<tr>
<tD VALign="top">
<fONT Size="2">
<p><TT CLass="monofont">"O"</tT></P>
</FOnt></td>
<td valign="top">
<font size="2">
<P>Any</p>
</fOnt></tD>
<td vaLign="top">
<FONT size="2">
<P><TT Class="monofont">PyObject *</TT></P>
</Font></tD>
<TD Valign="top">
<font size="2">
<p>Any Python object. The object is unchanged except for its reference count, which is incremented by <tt clasS="monofont">1</tt>. If a <Tt clAss="monofont">NULL</tt> pointer is given, a <Tt clASS="monofont">NULL</Tt> pointer is returned.</p>
</foNT></TD>
</tr>
<tr>
<TD VAlign="top">
<FONT size="2">
<p><tt class="monofont">"O&"</tt></p>
</font></tD>
<td ValiGn="top">
<fonT sizE="2">
<P>Any</P>
</Font></tD>
<TD ValigN="top">
<FONt sizE="2">
<P><I><Tt class="monofont">converter</tt></i>
<tt class="monofont">, </tt><i><tT clAss="monofont">any</tT></i>
</p>
</foNt></td>
<TD VAlign="top">
<FONT size="2">
<P>C data processed through a converter function.</P>
</FOnt></td>
</TR>
<TR>
<td valign="top">
<font size="2">
<p><tt cLasS="monofont">"S"</tt></p>
</Font></tD>
<td vALIGn="top">
<fonT SIZe="2">
<p>String</p>
</fONT></Td>
<td vALIGn="top">
<font size="2">
<p><tt class="monofont">PyObject *</tt></p>
</FonT></td>
<tD valiGn="top">
<foNT SIze="2">
<p>Same as <tT CLAss="monofont">"O"</tt>.</P>
</FONt></td>
</tR>
<TR>
<Td valign="top">
<font size="2">
<p><tt clAss="monofont">"U"</Tt></p>
</fOnt></td>
<Td vaLIGN="top">
<font SIZE="2">
<p>Unicode</p>
</foNT></TD>
<td vaLIGN="top">
<font size="2">
<p><tt class="monofont">PyObject *</tt></p>
</fOnt></Td>
<td ValigN="top">
<fonT SIZe="2">
<p>Same as <tt CLASs="monofont">"O"</tt>.</p>
</FONT></td>
</tr>
<TR>
<TD valign="top">
<font size="2">
<p><tt claSs="monofont">"N"</tT></p>
</foNt></td>
<tD valIGN="top">
<Font sIZE="2">
<P>Any</p>
</fonT></TD>
<Td valIGN="top">
<Font size="2">
<p><tt class="monofont">PyObject *</tt></p>
</foNt></tD>
<td vAlign="top">
<Font SIZE="2">
<p>Same as <tt cLASS="monofont">"O"</tt> except that the reference count is not incremented.</p>
</fONT></Td>
</tr>
<tR>
<TD Valign="top">
<font size="2">
<p><tt clasS="monofont">"(</tt><I><tt cLass="monofont">items</tT></i>
<tt CLASs="monofont">)"</tt></p>
</FONT></td>
<td VALIgn="top">
<foNT SIze="2">
<p>Tuple</p>
</font></td>
<td valign="top">
<foNt sIze="2">
<p><I><tt clAss="monofont">vars</tT></I>
</P>
</Font></tD>
<TD ValigN="top">
<FONt sizE="2">
<P>Creates a tuple of items. <I><Tt class="monofont">items</tt></i>
is a string of format specifiers from this table. <i><tt class="monofont">vars</tt></i>
is a list of C variables corresponding to the items in <I><tt ClasS="monofont">items</tt></i>
.</p>
</Font></TD>
</TR>
<tr>
<td VALIgn="top">
<foNT SIze="2">
<p><tT CLAss="monofont">"[</tt><i><tt class="monofont">items</tt></i>
<tt claSs="monofont">]"</tT></p>
</foNt></td>
<tD valIGN="top">
<Font sIZE="2">
<P>List</p>
</fonT></TD>
<Td valIGN="top">
<Font size="2">
<p><i><tt class="monofont">vars</tt></i>
</p>
</FonT></td>
<tD valiGn="top">
<foNT SIze="2">
<p>Creates a list of items. <i><TT CLass="monofont">items</tT></I>
is a string of format specifiers. <I><Tt claSS="monofont">vars</TT></i>
is a list of C variables corresponding to the items in <i><tt class="monofont">items</tt></i>
.</p>
</font></td>
</tR>
<tr>
<Td vaLign="top">
<fOnt sIZE="2">
<P><tt clASS="monofont">"{</Tt><i><tt CLASs="monofont">items</tt></i>
<TT CLass="monofont">}"</tt></p>
</font></td>
<td valign="top">
<FonT sizE="2">
<p>Dictionary</p>
</foNt></td>
<TD VAlign="top">
<FONT size="2">
<P><I><TT clasS="monofont">vars</TT></I>
</p>
</font></td>
<td valign="top">
<font sIze="2">
<P>Creates a dictionary of items.</p>
</foNt></td>
</tR>
</colGROUp>
</tabLE></P>
<P>Examples:</p>
<pre>
Py_BuildValue("") None
Py_BuildValue("i",37) 37
Py_BuildValue("ids",37,3.4,"hello") (37, 3.5, "hello")
Py_BuildValue("s#","hello",4) "hell"
Py_BuildValue("()") ()
Py_BuildValue("(i)",37) (37,)
Py_BuildValue("[ii]",1,2) [1,2]
Py_BuildValue("[i,i]",1,2) [1,2]
Py_BuildValue("{s:i,s:i}","x",1,"y",2) {'x':1, 'y':2} </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="125.html" title="Converting Data from Python to C"><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=126" target="_blank" title="Make a public or private annnotation">Make Note</a> | <a href="126.html" title="Use a Safari bookmark to remember this section">Bookmark</a></font></td><td align=right width="15%" class="headingsubbarbg"><a href="127.html" title="Error Handling"><font size="1">CONTINUE ></font></a></td></TR></TABLE>
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