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<H1><A NAME="SECTION008800000000000000000">
6.8 <tt class="module">popen2</tt> --
Subprocesses with accessible I/O streams</A>
</H1>
<P>
<p class='availability'>Availability: <span
class='platform'>Unix, Windows</span>.</p>
<P>
This module allows you to spawn processes and connect to their
input/output/error pipes and obtain their return codes under
Unix and Windows.
<P>
Note that starting with Python 2.0, this functionality is available
using functions from the <tt class='module'><a href="module-os.html" tppabs="http://www.python.org/doc/current/lib/module-os.html">os</a></tt> module which have the same
names as the factory functions here, but the order of the return
values is more intuitive in the <tt class='module'><a href="module-os.html" tppabs="http://www.python.org/doc/current/lib/module-os.html">os</a></tt> module variants.
<P>
The primary interface offered by this module is a trio of factory
functions. For each of these, if <var>bufsize</var> is specified,
it specifies the buffer size for the I/O pipes. <var>mode</var>, if
provided, should be the string <code>'b'</code> or <code>'t'</code>; on Windows
this is needed to determine whether the file objects should be opened
in binary or text mode. The default value for <var>mode</var> is
<code>'t'</code>.
<P>
<dl><dt><b><a name='l2h-1118'><tt class='function'>popen2</tt></a></b> (<var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><big>]</big>)
<dd>
Executes <var>cmd</var> as a sub-process. Returns the file objects
<code>(<var>child_stdout</var>, <var>child_stdin</var>)</code>.
</dl>
<P>
<dl><dt><b><a name='l2h-1119'><tt class='function'>popen3</tt></a></b> (<var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><big>]</big>)
<dd>
Executes <var>cmd</var> as a sub-process. Returns the file objects
<code>(<var>child_stdout</var>, <var>child_stdin</var>, <var>child_stderr</var>)</code>.
</dl>
<P>
<dl><dt><b><a name='l2h-1120'><tt class='function'>popen4</tt></a></b> (<var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><big>]</big>)
<dd>
Executes <var>cmd</var> as a sub-process. Returns the file objects
<code>(<var>child_stdout_and_stderr</var>, <var>child_stdin</var>)</code>.
New in version 2.0.
</dl>
<P>
On Unix, a class defining the objects returned by the factory
functions is also available. These are not used for the Windows
implementation, and are not available on that platform.
<P>
<dl><dt><b><a name='l2h-1121'><tt class='class'>Popen3</tt></a></b> (<var>cmd</var><big>[</big><var>, capturestderr</var><big>[</big><var>, bufsize</var><big>]</big><big>]</big>)
<dd>
This class represents a child process. Normally, <tt class="class">Popen3</tt>
instances are created using the <tt class="function">popen2()</tt> and
<tt class="function">popen3()</tt> factory functions described above.
<P>
If not using one off the helper functions to create <tt class="class">Popen3</tt>
objects, the parameter <var>cmd</var> is the shell command to execute in a
sub-process. The <var>capturestderr</var> flag, if true, specifies that
the object should capture standard error output of the child process.
The default is false. If the <var>bufsize</var> parameter is specified, it
specifies the size of the I/O buffers to/from the child process.
</dl>
<P>
<dl><dt><b><a name='l2h-1122'><tt class='class'>Popen4</tt></a></b> (<var>cmd</var><big>[</big><var>, bufsize</var><big>]</big>)
<dd>
Similar to <tt class="class">Popen3</tt>, but always captures standard error into the
same file object as standard output. These are typically created
using <tt class="function">popen4()</tt>.
New in version 2.0.
</dl>
<P>
<p><hr>
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<LI><A NAME="tex2html2347"
href="popen3-objects.html" tppabs="http://www.python.org/doc/current/lib/popen3-objects.html">6.8.1 Popen3 and Popen4 Objects </A>
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