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<div class="section" id="subprocesses">
<span id="asyncio-subprocess"></span><h1>Subprocesses<a class="headerlink" href="#subprocesses" title="Permalink to this headline">¶</a></h1>
<p>This section describes high-level async/await asyncio APIs to
create and manage subprocesses.</p>
<p id="asyncio-example-subprocess-shell">Here’s an example of how asyncio can run a shell command and
obtain its result:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">run</span><span class="p">(</span><span class="n">cmd</span><span class="p">):</span>
<span class="n">proc</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_subprocess_shell</span><span class="p">(</span>
<span class="n">cmd</span><span class="p">,</span>
<span class="n">stdout</span><span class="o">=</span><span class="n">asyncio</span><span class="o">.</span><span class="n">subprocess</span><span class="o">.</span><span class="n">PIPE</span><span class="p">,</span>
<span class="n">stderr</span><span class="o">=</span><span class="n">asyncio</span><span class="o">.</span><span class="n">subprocess</span><span class="o">.</span><span class="n">PIPE</span><span class="p">)</span>
<span class="n">stdout</span><span class="p">,</span> <span class="n">stderr</span> <span class="o">=</span> <span class="k">await</span> <span class="n">proc</span><span class="o">.</span><span class="n">communicate</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'[</span><span class="si">{</span><span class="n">cmd</span><span class="si">!r}</span><span class="s1"> exited with </span><span class="si">{</span><span class="n">proc</span><span class="o">.</span><span class="n">returncode</span><span class="si">}</span><span class="s1">]'</span><span class="p">)</span>
<span class="k">if</span> <span class="n">stdout</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'[stdout]</span><span class="se">\n</span><span class="si">{</span><span class="n">stdout</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="k">if</span> <span class="n">stderr</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'[stderr]</span><span class="se">\n</span><span class="si">{</span><span class="n">stderr</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">run</span><span class="p">(</span><span class="s1">'ls /zzz'</span><span class="p">))</span>
</pre></div>
</div>
<p>will print:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="s1">'ls /zzz'</span> <span class="n">exited</span> <span class="k">with</span> <span class="mi">1</span><span class="p">]</span>
<span class="p">[</span><span class="n">stderr</span><span class="p">]</span>
<span class="n">ls</span><span class="p">:</span> <span class="o">/</span><span class="n">zzz</span><span class="p">:</span> <span class="n">No</span> <span class="n">such</span> <span class="n">file</span> <span class="ow">or</span> <span class="n">directory</span>
</pre></div>
</div>
<p>Because all asyncio subprocess functions are asynchronous and asyncio
provides many tools to work with such functions, it is easy to execute
and monitor multiple subprocesses in parallel. It is indeed trivial
to modify the above example to run several commands simultaneously:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">gather</span><span class="p">(</span>
<span class="n">run</span><span class="p">(</span><span class="s1">'ls /zzz'</span><span class="p">),</span>
<span class="n">run</span><span class="p">(</span><span class="s1">'sleep 1; echo "hello"'</span><span class="p">))</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<p>See also the <a class="reference internal" href="#examples">Examples</a> subsection.</p>
<div class="section" id="creating-subprocesses">
<h2>Creating Subprocesses<a class="headerlink" href="#creating-subprocesses" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.create_subprocess_exec">
<em class="property">coroutine </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">create_subprocess_exec</code><span class="sig-paren">(</span><em class="sig-param">program</em>, <em class="sig-param">*args</em>, <em class="sig-param">stdin=None</em>, <em class="sig-param">stdout=None</em>, <em class="sig-param">stderr=None</em>, <em class="sig-param">loop=None</em>, <em class="sig-param">limit=None</em>, <em class="sig-param">**kwds</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.create_subprocess_exec" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a subprocess.</p>
<p>The <em>limit</em> argument sets the buffer limit for <a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>
wrappers for <code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stdout</span></code> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stderr</span></code>
(if <a class="reference internal" href="subprocess.html#subprocess.PIPE" title="subprocess.PIPE"><code class="xref py py-attr docutils literal notranslate"><span class="pre">subprocess.PIPE</span></code></a> is passed to <em>stdout</em> and <em>stderr</em> arguments).</p>
<p>Return a <a class="reference internal" href="#asyncio.asyncio.subprocess.Process" title="asyncio.asyncio.subprocess.Process"><code class="xref py py-class docutils literal notranslate"><span class="pre">Process</span></code></a> instance.</p>
<p>See the documentation of <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a> for other
parameters.</p>
</dd></dl>
<dl class="function">
<dt id="asyncio.create_subprocess_shell">
<em class="property">coroutine </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">create_subprocess_shell</code><span class="sig-paren">(</span><em class="sig-param">cmd</em>, <em class="sig-param">stdin=None</em>, <em class="sig-param">stdout=None</em>, <em class="sig-param">stderr=None</em>, <em class="sig-param">loop=None</em>, <em class="sig-param">limit=None</em>, <em class="sig-param">**kwds</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.create_subprocess_shell" title="Permalink to this definition">¶</a></dt>
<dd><p>Run the <em>cmd</em> shell command.</p>
<p>The <em>limit</em> argument sets the buffer limit for <a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>
wrappers for <code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stdout</span></code> and <code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stderr</span></code>
(if <a class="reference internal" href="subprocess.html#subprocess.PIPE" title="subprocess.PIPE"><code class="xref py py-attr docutils literal notranslate"><span class="pre">subprocess.PIPE</span></code></a> is passed to <em>stdout</em> and <em>stderr</em> arguments).</p>
<p>Return a <a class="reference internal" href="#asyncio.asyncio.subprocess.Process" title="asyncio.asyncio.subprocess.Process"><code class="xref py py-class docutils literal notranslate"><span class="pre">Process</span></code></a> instance.</p>
<p>See the documentation of <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_shell()</span></code></a> for other
parameters.</p>
</dd></dl>
<div class="admonition important">
<p class="admonition-title">Important</p>
<p>It is the application’s responsibility to ensure that all whitespace and
special characters are quoted appropriately to avoid <a class="reference external" href="https://en.wikipedia.org/wiki/Shell_injection#Shell_injection">shell injection</a>
vulnerabilities. The <a class="reference internal" href="shlex.html#shlex.quote" title="shlex.quote"><code class="xref py py-func docutils literal notranslate"><span class="pre">shlex.quote()</span></code></a> function can be used to properly
escape whitespace and special shell characters in strings that are going
to be used to construct shell commands.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The default asyncio event loop implementation on <strong>Windows</strong> does not
support subprocesses. Subprocesses are available for Windows if a
<a class="reference internal" href="asyncio-eventloop.html#asyncio.ProactorEventLoop" title="asyncio.ProactorEventLoop"><code class="xref py py-class docutils literal notranslate"><span class="pre">ProactorEventLoop</span></code></a> is used.
See <a class="reference internal" href="asyncio-platforms.html#asyncio-windows-subprocess"><span class="std std-ref">Subprocess Support on Windows</span></a>
for details.</p>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>asyncio also has the following <em>low-level</em> APIs to work with subprocesses:
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_shell()</span></code></a>,
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_read_pipe" title="asyncio.loop.connect_read_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_read_pipe()</span></code></a>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_write_pipe()</span></code></a>,
as well as the <a class="reference internal" href="asyncio-protocol.html#asyncio-subprocess-transports"><span class="std std-ref">Subprocess Transports</span></a>
and <a class="reference internal" href="asyncio-protocol.html#asyncio-subprocess-protocols"><span class="std std-ref">Subprocess Protocols</span></a>.</p>
</div>
</div>
<div class="section" id="constants">
<h2>Constants<a class="headerlink" href="#constants" title="Permalink to this headline">¶</a></h2>
<dl class="data">
<dt id="asyncio.asyncio.subprocess.PIPE">
<code class="sig-prename descclassname">asyncio.subprocess.</code><code class="sig-name descname">PIPE</code><a class="headerlink" href="#asyncio.asyncio.subprocess.PIPE" title="Permalink to this definition">¶</a></dt>
<dd><p>Can be passed to the <em>stdin</em>, <em>stdout</em> or <em>stderr</em> parameters.</p>
<p>If <em>PIPE</em> is passed to <em>stdin</em> argument, the
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.stdin" title="asyncio.asyncio.subprocess.Process.stdin"><code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stdin</span></code></a> attribute
will point to a <a class="reference internal" href="asyncio-stream.html#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a> instance.</p>
<p>If <em>PIPE</em> is passed to <em>stdout</em> or <em>stderr</em> arguments, the
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.stdout" title="asyncio.asyncio.subprocess.Process.stdout"><code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stdout</span></code></a> and
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.stderr" title="asyncio.asyncio.subprocess.Process.stderr"><code class="xref py py-attr docutils literal notranslate"><span class="pre">Process.stderr</span></code></a>
attributes will point to <a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> instances.</p>
</dd></dl>
<dl class="data">
<dt id="asyncio.asyncio.subprocess.STDOUT">
<code class="sig-prename descclassname">asyncio.subprocess.</code><code class="sig-name descname">STDOUT</code><a class="headerlink" href="#asyncio.asyncio.subprocess.STDOUT" title="Permalink to this definition">¶</a></dt>
<dd><p>Special value that can be used as the <em>stderr</em> argument and indicates
that standard error should be redirected into standard output.</p>
</dd></dl>
<dl class="data">
<dt id="asyncio.asyncio.subprocess.DEVNULL">
<code class="sig-prename descclassname">asyncio.subprocess.</code><code class="sig-name descname">DEVNULL</code><a class="headerlink" href="#asyncio.asyncio.subprocess.DEVNULL" title="Permalink to this definition">¶</a></dt>
<dd><p>Special value that can be used as the <em>stdin</em>, <em>stdout</em> or <em>stderr</em> argument
to process creation functions. It indicates that the special file
<a class="reference internal" href="os.html#os.devnull" title="os.devnull"><code class="xref py py-data docutils literal notranslate"><span class="pre">os.devnull</span></code></a> will be used for the corresponding subprocess stream.</p>
</dd></dl>
</div>
<div class="section" id="interacting-with-subprocesses">
<h2>Interacting with Subprocesses<a class="headerlink" href="#interacting-with-subprocesses" title="Permalink to this headline">¶</a></h2>
<p>Both <a class="reference internal" href="#asyncio.create_subprocess_exec" title="asyncio.create_subprocess_exec"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_subprocess_exec()</span></code></a> and <a class="reference internal" href="#asyncio.create_subprocess_shell" title="asyncio.create_subprocess_shell"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_subprocess_shell()</span></code></a>
functions return instances of the <em>Process</em> class. <em>Process</em> is a high-level
wrapper that allows communicating with subprocesses and watching for
their completion.</p>
<dl class="class">
<dt id="asyncio.asyncio.subprocess.Process">
<em class="property">class </em><code class="sig-prename descclassname">asyncio.subprocess.</code><code class="sig-name descname">Process</code><a class="headerlink" href="#asyncio.asyncio.subprocess.Process" title="Permalink to this definition">¶</a></dt>
<dd><p>An object that wraps OS processes created by the
<a class="reference internal" href="#asyncio.create_subprocess_exec" title="asyncio.create_subprocess_exec"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_subprocess_exec()</span></code></a> and <a class="reference internal" href="#asyncio.create_subprocess_shell" title="asyncio.create_subprocess_shell"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_subprocess_shell()</span></code></a>
functions.</p>
<p>This class is designed to have a similar API to the
<a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate"><span class="pre">subprocess.Popen</span></code></a> class, but there are some
notable differences:</p>
<ul class="simple">
<li><p>unlike Popen, Process instances do not have an equivalent to
the <a class="reference internal" href="subprocess.html#subprocess.Popen.poll" title="subprocess.Popen.poll"><code class="xref py py-meth docutils literal notranslate"><span class="pre">poll()</span></code></a> method;</p></li>
<li><p>the <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.communicate" title="asyncio.asyncio.subprocess.Process.communicate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">communicate()</span></code></a> and
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.wait" title="asyncio.asyncio.subprocess.Process.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">wait()</span></code></a> methods don’t have a
<em>timeout</em> parameter: use the <a class="reference internal" href="asyncio-task.html#asyncio.wait_for" title="asyncio.wait_for"><code class="xref py py-func docutils literal notranslate"><span class="pre">wait_for()</span></code></a> function;</p></li>
<li><p>the <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.wait" title="asyncio.asyncio.subprocess.Process.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Process.wait()</span></code></a> method
is asynchronous, whereas <a class="reference internal" href="subprocess.html#subprocess.Popen.wait" title="subprocess.Popen.wait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">subprocess.Popen.wait()</span></code></a> method
is implemented as a blocking busy loop;</p></li>
<li><p>the <em>universal_newlines</em> parameter is not supported.</p></li>
</ul>
<p>This class is <a class="reference internal" href="asyncio-dev.html#asyncio-multithreading"><span class="std std-ref">not thread safe</span></a>.</p>
<p>See also the <a class="reference internal" href="#asyncio-subprocess-threads"><span class="std std-ref">Subprocess and Threads</span></a>
section.</p>
<dl class="method">
<dt id="asyncio.asyncio.subprocess.Process.wait">
<em class="property">coroutine </em><code class="sig-name descname">wait</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.wait" title="Permalink to this definition">¶</a></dt>
<dd><p>Wait for the child process to terminate.</p>
<p>Set and return the <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.returncode" title="asyncio.asyncio.subprocess.Process.returncode"><code class="xref py py-attr docutils literal notranslate"><span class="pre">returncode</span></code></a> attribute.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>This method can deadlock when using <code class="docutils literal notranslate"><span class="pre">stdout=PIPE</span></code> or
<code class="docutils literal notranslate"><span class="pre">stderr=PIPE</span></code> and the child process generates so much output
that it blocks waiting for the OS pipe buffer to accept
more data. Use the <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.communicate" title="asyncio.asyncio.subprocess.Process.communicate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">communicate()</span></code></a> method when using pipes
to avoid this condition.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="asyncio.asyncio.subprocess.Process.communicate">
<em class="property">coroutine </em><code class="sig-name descname">communicate</code><span class="sig-paren">(</span><em class="sig-param">input=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.communicate" title="Permalink to this definition">¶</a></dt>
<dd><p>Interact with process:</p>
<ol class="arabic simple">
<li><p>send data to <em>stdin</em> (if <em>input</em> is not <code class="docutils literal notranslate"><span class="pre">None</span></code>);</p></li>
<li><p>read data from <em>stdout</em> and <em>stderr</em>, until EOF is reached;</p></li>
<li><p>wait for process to terminate.</p></li>
</ol>
<p>The optional <em>input</em> argument is the data (<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> object)
that will be sent to the child process.</p>
<p>Return a tuple <code class="docutils literal notranslate"><span class="pre">(stdout_data,</span> <span class="pre">stderr_data)</span></code>.</p>
<p>If either <a class="reference internal" href="exceptions.html#BrokenPipeError" title="BrokenPipeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">BrokenPipeError</span></code></a> or <a class="reference internal" href="exceptions.html#ConnectionResetError" title="ConnectionResetError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ConnectionResetError</span></code></a>
exception is raised when writing <em>input</em> into <em>stdin</em>, the
exception is ignored. This condition occurs when the process
exits before all data are written into <em>stdin</em>.</p>
<p>If it is desired to send data to the process’ <em>stdin</em>,
the process needs to be created with <code class="docutils literal notranslate"><span class="pre">stdin=PIPE</span></code>. Similarly,
to get anything other than <code class="docutils literal notranslate"><span class="pre">None</span></code> in the result tuple, the
process has to be created with <code class="docutils literal notranslate"><span class="pre">stdout=PIPE</span></code> and/or
<code class="docutils literal notranslate"><span class="pre">stderr=PIPE</span></code> arguments.</p>
<p>Note, that the data read is buffered in memory, so do not use
this method if the data size is large or unlimited.</p>
</dd></dl>
<dl class="method">
<dt id="asyncio.asyncio.subprocess.Process.send_signal">
<code class="sig-name descname">send_signal</code><span class="sig-paren">(</span><em class="sig-param">signal</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.send_signal" title="Permalink to this definition">¶</a></dt>
<dd><p>Sends the signal <em>signal</em> to the child process.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>On Windows, <code class="xref py py-data docutils literal notranslate"><span class="pre">SIGTERM</span></code> is an alias for <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.terminate" title="asyncio.asyncio.subprocess.Process.terminate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">terminate()</span></code></a>.
<code class="docutils literal notranslate"><span class="pre">CTRL_C_EVENT</span></code> and <code class="docutils literal notranslate"><span class="pre">CTRL_BREAK_EVENT</span></code> can be sent to processes
started with a <em>creationflags</em> parameter which includes
<code class="docutils literal notranslate"><span class="pre">CREATE_NEW_PROCESS_GROUP</span></code>.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="asyncio.asyncio.subprocess.Process.terminate">
<code class="sig-name descname">terminate</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.terminate" title="Permalink to this definition">¶</a></dt>
<dd><p>Stop the child process.</p>
<p>On POSIX systems this method sends <a class="reference internal" href="signal.html#signal.SIGTERM" title="signal.SIGTERM"><code class="xref py py-data docutils literal notranslate"><span class="pre">signal.SIGTERM</span></code></a> to the
child process.</p>
<p>On Windows the Win32 API function <code class="xref c c-func docutils literal notranslate"><span class="pre">TerminateProcess()</span></code> is
called to stop the child process.</p>
</dd></dl>
<dl class="method">
<dt id="asyncio.asyncio.subprocess.Process.kill">
<code class="sig-name descname">kill</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.kill" title="Permalink to this definition">¶</a></dt>
<dd><p>Kill the child.</p>
<p>On POSIX systems this method sends <code class="xref py py-data docutils literal notranslate"><span class="pre">SIGKILL</span></code> to the child
process.</p>
<p>On Windows this method is an alias for <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.terminate" title="asyncio.asyncio.subprocess.Process.terminate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">terminate()</span></code></a>.</p>
</dd></dl>
<dl class="attribute">
<dt id="asyncio.asyncio.subprocess.Process.stdin">
<code class="sig-name descname">stdin</code><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.stdin" title="Permalink to this definition">¶</a></dt>
<dd><p>Standard input stream (<a class="reference internal" href="asyncio-stream.html#asyncio.StreamWriter" title="asyncio.StreamWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamWriter</span></code></a>) or <code class="docutils literal notranslate"><span class="pre">None</span></code>
if the process was created with <code class="docutils literal notranslate"><span class="pre">stdin=None</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="asyncio.asyncio.subprocess.Process.stdout">
<code class="sig-name descname">stdout</code><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.stdout" title="Permalink to this definition">¶</a></dt>
<dd><p>Standard output stream (<a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>) or <code class="docutils literal notranslate"><span class="pre">None</span></code>
if the process was created with <code class="docutils literal notranslate"><span class="pre">stdout=None</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="asyncio.asyncio.subprocess.Process.stderr">
<code class="sig-name descname">stderr</code><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.stderr" title="Permalink to this definition">¶</a></dt>
<dd><p>Standard error stream (<a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a>) or <code class="docutils literal notranslate"><span class="pre">None</span></code>
if the process was created with <code class="docutils literal notranslate"><span class="pre">stderr=None</span></code>.</p>
</dd></dl>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>Use the <a class="reference internal" href="#asyncio.asyncio.subprocess.Process.communicate" title="asyncio.asyncio.subprocess.Process.communicate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">communicate()</span></code></a> method rather than
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.stdin" title="asyncio.asyncio.subprocess.Process.stdin"><code class="xref py py-attr docutils literal notranslate"><span class="pre">process.stdin.write()</span></code></a>,
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.stdout" title="asyncio.asyncio.subprocess.Process.stdout"><code class="xref py py-attr docutils literal notranslate"><span class="pre">await</span> <span class="pre">process.stdout.read()</span></code></a> or
<a class="reference internal" href="#asyncio.asyncio.subprocess.Process.stderr" title="asyncio.asyncio.subprocess.Process.stderr"><code class="xref py py-attr docutils literal notranslate"><span class="pre">await</span> <span class="pre">process.stderr.read</span></code></a>.
This avoids deadlocks due to streams pausing reading or writing
and blocking the child process.</p>
</div>
<dl class="attribute">
<dt id="asyncio.asyncio.subprocess.Process.pid">
<code class="sig-name descname">pid</code><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.pid" title="Permalink to this definition">¶</a></dt>
<dd><p>Process identification number (PID).</p>
<p>Note that for processes created by the <a class="reference internal" href="#asyncio.create_subprocess_shell" title="asyncio.create_subprocess_shell"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_subprocess_shell()</span></code></a>
function, this attribute is the PID of the spawned shell.</p>
</dd></dl>
<dl class="attribute">
<dt id="asyncio.asyncio.subprocess.Process.returncode">
<code class="sig-name descname">returncode</code><a class="headerlink" href="#asyncio.asyncio.subprocess.Process.returncode" title="Permalink to this definition">¶</a></dt>
<dd><p>Return code of the process when it exits.</p>
<p>A <code class="docutils literal notranslate"><span class="pre">None</span></code> value indicates that the process has not terminated yet.</p>
<p>A negative value <code class="docutils literal notranslate"><span class="pre">-N</span></code> indicates that the child was terminated
by signal <code class="docutils literal notranslate"><span class="pre">N</span></code> (POSIX only).</p>
</dd></dl>
</dd></dl>
<div class="section" id="subprocess-and-threads">
<span id="asyncio-subprocess-threads"></span><h3>Subprocess and Threads<a class="headerlink" href="#subprocess-and-threads" title="Permalink to this headline">¶</a></h3>
<p>Standard asyncio event loop supports running subprocesses from
different threads, but there are limitations:</p>
<ul class="simple">
<li><p>An event loop must run in the main thread.</p></li>
<li><p>The child watcher must be instantiated in the main thread
before executing subprocesses from other threads. Call the
<a class="reference internal" href="asyncio-policy.html#asyncio.get_child_watcher" title="asyncio.get_child_watcher"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_child_watcher()</span></code></a> function in the main thread to instantiate
the child watcher.</p></li>
</ul>
<p>Note that alternative event loop implementations might not share
the above limitations; please refer to their documentation.</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p>The <a class="reference internal" href="asyncio-dev.html#asyncio-multithreading"><span class="std std-ref">Concurrency and multithreading in asyncio</span></a> section.</p>
</div>
</div>
<div class="section" id="examples">
<h3>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h3>
<p>An example using the <a class="reference internal" href="#asyncio.asyncio.subprocess.Process" title="asyncio.asyncio.subprocess.Process"><code class="xref py py-class docutils literal notranslate"><span class="pre">Process</span></code></a> class to
control a subprocess and the <a class="reference internal" href="asyncio-stream.html#asyncio.StreamReader" title="asyncio.StreamReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">StreamReader</span></code></a> class to read from
its standard output.</p>
<p id="asyncio-example-create-subprocess-exec">The subprocess is created by the <a class="reference internal" href="#asyncio.create_subprocess_exec" title="asyncio.create_subprocess_exec"><code class="xref py py-func docutils literal notranslate"><span class="pre">create_subprocess_exec()</span></code></a>
function:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">get_date</span><span class="p">():</span>
<span class="n">code</span> <span class="o">=</span> <span class="s1">'import datetime; print(datetime.datetime.now())'</span>
<span class="c1"># Create the subprocess; redirect the standard output</span>
<span class="c1"># into a pipe.</span>
<span class="n">proc</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_subprocess_exec</span><span class="p">(</span>
<span class="n">sys</span><span class="o">.</span><span class="n">executable</span><span class="p">,</span> <span class="s1">'-c'</span><span class="p">,</span> <span class="n">code</span><span class="p">,</span>
<span class="n">stdout</span><span class="o">=</span><span class="n">asyncio</span><span class="o">.</span><span class="n">subprocess</span><span class="o">.</span><span class="n">PIPE</span><span class="p">)</span>
<span class="c1"># Read one line of output.</span>
<span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">proc</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span>
<span class="n">line</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">'ascii'</span><span class="p">)</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span>
<span class="c1"># Wait for the subprocess exit.</span>
<span class="k">await</span> <span class="n">proc</span><span class="o">.</span><span class="n">wait</span><span class="p">()</span>
<span class="k">return</span> <span class="n">line</span>
<span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">platform</span> <span class="o">==</span> <span class="s2">"win32"</span><span class="p">:</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">set_event_loop_policy</span><span class="p">(</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">WindowsProactorEventLoopPolicy</span><span class="p">())</span>
<span class="n">date</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">get_date</span><span class="p">())</span>
<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"Current date: </span><span class="si">{</span><span class="n">date</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
</pre></div>
</div>
<p>See also the <a class="reference internal" href="asyncio-protocol.html#asyncio-example-subprocess-proto"><span class="std std-ref">same example</span></a>
written using low-level APIs.</p>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Subprocesses</a><ul>
<li><a class="reference internal" href="#creating-subprocesses">Creating Subprocesses</a></li>
<li><a class="reference internal" href="#constants">Constants</a></li>
<li><a class="reference internal" href="#interacting-with-subprocesses">Interacting with Subprocesses</a><ul>
<li><a class="reference internal" href="#subprocess-and-threads">Subprocess and Threads</a></li>
<li><a class="reference internal" href="#examples">Examples</a></li>
</ul>
</li>
</ul>
</li>
</ul>
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