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<H1><A NAME="SECTION008900000000000000000">
6.9 <tt class="module">popen2</tt> --
         Subprocesses with accessible I/O streams</A>
</H1>

<P>
<A NAME="module-popen2"></A>  
<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
<span class="Unix">Unix</span> 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">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">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>
On <span class="Unix">Unix</span>, <var>cmd</var> may be a sequence, in which case arguments will be passed
directly to the program without shell intervention (as with
<tt class="function">os.spawnv()</tt>). If <var>cmd</var> is a string it will be passed to the
shell (as with <tt class="function">os.system()</tt>).

<P>
The only way to retrieve the return codes for the child processes is
by using the <tt class="method">poll()</tt> or <tt class="method">wait()</tt> methods on the
<tt class="class">Popen3</tt> and <tt class="class">Popen4</tt> classes; these are only available on
<span class="Unix">Unix</span>.  This information is not available when using the
<tt class="function">popen2()</tt>, <tt class="function">popen3()</tt>, and <tt class="function">popen4()</tt>
functions, or the equivalent functions in the <tt class="module"><a href="module-os.html">os</a></tt> module.
(Note that the tuples returned by the <tt class="module"><a href="module-os.html">os</a></tt> module's functions
are in a different order from the ones returned by the <tt class="module">popen2</tt>
module.)

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1844' xml:id='l2h-1844' class="function">popen2</tt></b>(</nobr></td>
  <td><var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<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><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1845' xml:id='l2h-1845' class="function">popen3</tt></b>(</nobr></td>
  <td><var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<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><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-1846' xml:id='l2h-1846' class="function">popen4</tt></b>(</nobr></td>
  <td><var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<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>.

<span class="versionnote">New in version 2.0.</span>

</dl>

<P>
On <span class="Unix">Unix</span>, 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><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-1847' xml:id='l2h-1847' class="class">Popen3</tt></b>(</nobr></td>
  <td><var>cmd</var><big>[</big><var>, capturestderr</var><big>[</big><var>, bufsize</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<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 of 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><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-1848' xml:id='l2h-1848' class="class">Popen4</tt></b>(</nobr></td>
  <td><var>cmd</var><big>[</big><var>, bufsize</var><big>]</big><var></var>)</td></tr></table></dt>
<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>.

<span class="versionnote">New in version 2.0.</span>

</dl>

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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	54
	55	<H1><A NAME="SECTION008900000000000000000">
	56	6.9 <tt class="module">popen2</tt> --
	57	Subprocesses with accessible I/O streams</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-popen2"></A>
	62	<p class="availability">Availability: <span
	63	class="platform">Unix, Windows</span>.</p>
	64
65	<P>
66	This module allows you to spawn processes and connect to their
67	input/output/error pipes and obtain their return codes under
68	<span class="Unix">Unix</span> and Windows.
69
70	<P>
71	Note that starting with Python 2.0, this functionality is available
72	using functions from the <tt class="module"><a href="module-os.html">os</a></tt> module which have the same
73	names as the factory functions here, but the order of the return
74	values is more intuitive in the <tt class="module"><a href="module-os.html">os</a></tt> module variants.
75
76	<P>
77	The primary interface offered by this module is a trio of factory
78	functions. For each of these, if <var>bufsize</var> is specified,
79	it specifies the buffer size for the I/O pipes. <var>mode</var>, if
80	provided, should be the string <code>'b'</code> or <code>'t'</code>; on Windows
81	this is needed to determine whether the file objects should be opened
82	in binary or text mode. The default value for <var>mode</var> is
83	<code>'t'</code>.
84
85	<P>
86	On <span class="Unix">Unix</span>, <var>cmd</var> may be a sequence, in which case arguments will be passed
87	directly to the program without shell intervention (as with
88	<tt class="function">os.spawnv()</tt>). If <var>cmd</var> is a string it will be passed to the
89	shell (as with <tt class="function">os.system()</tt>).
90
91	<P>
92	The only way to retrieve the return codes for the child processes is
93	by using the <tt class="method">poll()</tt> or <tt class="method">wait()</tt> methods on the
94	<tt class="class">Popen3</tt> and <tt class="class">Popen4</tt> classes; these are only available on
95	<span class="Unix">Unix</span>. This information is not available when using the
96	<tt class="function">popen2()</tt>, <tt class="function">popen3()</tt>, and <tt class="function">popen4()</tt>
97	functions, or the equivalent functions in the <tt class="module"><a href="module-os.html">os</a></tt> module.
98	(Note that the tuples returned by the <tt class="module"><a href="module-os.html">os</a></tt> module's functions
99	are in a different order from the ones returned by the <tt class="module">popen2</tt>
100	module.)
101
102	<P>
103	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
104	<td><nobr><b><tt id='l2h-1844' xml:id='l2h-1844' class="function">popen2</tt></b>(</nobr></td>
105	<td><var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
106	<dd>
107	Executes <var>cmd</var> as a sub-process. Returns the file objects
108	<code>(<var>child_stdout</var>, <var>child_stdin</var>)</code>.
109	</dl>
110
111	<P>
112	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
113	<td><nobr><b><tt id='l2h-1845' xml:id='l2h-1845' class="function">popen3</tt></b>(</nobr></td>
114	<td><var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
115	<dd>
116	Executes <var>cmd</var> as a sub-process. Returns the file objects
117	<code>(<var>child_stdout</var>, <var>child_stdin</var>, <var>child_stderr</var>)</code>.
118	</dl>
119
120	<P>
121	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
122	<td><nobr><b><tt id='l2h-1846' xml:id='l2h-1846' class="function">popen4</tt></b>(</nobr></td>
123	<td><var>cmd</var><big>[</big><var>, bufsize</var><big>[</big><var>, mode</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
124	<dd>
125	Executes <var>cmd</var> as a sub-process. Returns the file objects
126	<code>(<var>child_stdout_and_stderr</var>, <var>child_stdin</var>)</code>.
127
128	<span class="versionnote">New in version 2.0.</span>
129
130	</dl>
131
132	<P>
133	On <span class="Unix">Unix</span>, a class defining the objects returned by the factory
134	functions is also available. These are not used for the Windows
135	implementation, and are not available on that platform.
136
137	<P>
138	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
139	<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-1847' xml:id='l2h-1847' class="class">Popen3</tt></b>(</nobr></td>
140	<td><var>cmd</var><big>[</big><var>, capturestderr</var><big>[</big><var>, bufsize</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
141	<dd>
142	This class represents a child process. Normally, <tt class="class">Popen3</tt>
143	instances are created using the <tt class="function">popen2()</tt> and
144	<tt class="function">popen3()</tt> factory functions described above.
145
146	<P>
147	If not using one of the helper functions to create <tt class="class">Popen3</tt>
148	objects, the parameter <var>cmd</var> is the shell command to execute in a
149	sub-process. The <var>capturestderr</var> flag, if true, specifies that
150	the object should capture standard error output of the child process.
151	The default is false. If the <var>bufsize</var> parameter is specified, it
152	specifies the size of the I/O buffers to/from the child process.
153	</dl>
154
155	<P>
156	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
157	<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-1848' xml:id='l2h-1848' class="class">Popen4</tt></b>(</nobr></td>
158	<td><var>cmd</var><big>[</big><var>, bufsize</var><big>]</big><var></var>)</td></tr></table></dt>
159	<dd>
160	Similar to <tt class="class">Popen3</tt>, but always captures standard error into the
161	same file object as standard output. These are typically created
162	using <tt class="function">popen4()</tt>.
163
164	<span class="versionnote">New in version 2.0.</span>
165
166	</dl>
167
168	<P>
169
170	<p><br /></p><hr class='online-navigation' />
171	<div class='online-navigation'>
172	<!--Table of Child-Links-->
173	<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
174
175	<UL CLASS="ChildLinks">
176	<LI><A href="popen3-objects.html">6.9.1 Popen3 and Popen4 Objects</a>
177	<LI><A href="popen2-flow-control.html">6.9.2 Flow Control Issues</a>
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216	<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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