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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 | |
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| 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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