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.. currentmodule:: asyncio
Subprocess
==========
Create a subprocess
-------------------
.. function:: create_subprocess_shell(cmd, stdin=None, stdout=None, stderr=None, loop=None, limit=None, \*\*kwds)
Run the shell command *cmd* given as a string. Return a :class:`~asyncio.subprocess.Process`
instance.
This function is a :ref:`coroutine <coroutine>`.
.. function:: create_subprocess_exec(\*args, stdin=None, stdout=None, stderr=None, loop=None, limit=None, \*\*kwds)
Create a subprocess. Return a :class:`~asyncio.subprocess.Process` instance.
This function is a :ref:`coroutine <coroutine>`.
Use the :meth:`BaseEventLoop.connect_read_pipe` and
:meth:`BaseEventLoop.connect_write_pipe` methods to connect pipes.
.. seealso::
The :meth:`BaseEventLoop.subprocess_exec` and
:meth:`BaseEventLoop.subprocess_shell` methods.
Constants
---------
.. data:: asyncio.subprocess.PIPE
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
to :func:`create_subprocess_shell` and :func:`create_subprocess_exec` and
indicates that a pipe to the standard stream should be opened.
.. data:: asyncio.subprocess.STDOUT
Special value that can be used as the *stderr* argument to
:func:`create_subprocess_shell` and :func:`create_subprocess_exec` and
indicates that standard error should go into the same handle as standard
output.
.. data:: asyncio.subprocess.DEVNULL
Special value that can be used as the *stdin*, *stdout* or *stderr* argument
to :func:`create_subprocess_shell` and :func:`create_subprocess_exec` and
indicates that the special file :data:`os.devnull` will be used.
Process
-------
.. class:: asyncio.subprocess.Process
.. attribute:: pid
The identifier of the process.
Note that if you set the *shell* argument to ``True``, this is the
process identifier of the spawned shell.
.. attribute:: returncode
Return code of the process when it exited. A ``None`` value indicates
that the process has not terminated yet.
A negative value ``-N`` indicates that the child was terminated by signal
``N`` (Unix only).
.. attribute:: stdin
Standard input stream (write), ``None`` if the process was created with
``stdin=None``.
.. attribute:: stdout
Standard output stream (read), ``None`` if the process was created with
``stdout=None``.
.. attribute:: stderr
Standard error stream (read), ``None`` if the process was created with
``stderr=None``.
.. method:: communicate(input=None)
Interact with process: Send data to stdin. Read data from stdout and
stderr, until end-of-file is reached. Wait for process to terminate.
The optional *input* argument should be data to be sent to the child
process, or ``None``, if no data should be sent to the child. The type
of *input* must be bytes.
:meth:`communicate` returns a tuple ``(stdoutdata, stderrdata)``.
Note that if you want to send data to the process's stdin, you need to
create the Process object with ``stdin=PIPE``. Similarly, to get anything
other than ``None`` in the result tuple, you need to give ``stdout=PIPE``
and/or ``stderr=PIPE`` too.
.. note::
The data read is buffered in memory, so do not use this method if the
data size is large or unlimited.
This method is a :ref:`coroutine <coroutine>`.
.. method:: kill()
Kills the child. On Posix OSs the function sends :py:data:`SIGKILL` to
the child. On Windows :meth:`kill` is an alias for :meth:`terminate`.
.. method:: send_signal(signal)
Sends the signal *signal* to the child process.
.. note::
On Windows, :py:data:`SIGTERM` is an alias for :meth:`terminate`.
``CTRL_C_EVENT`` and ``CTRL_BREAK_EVENT`` can be sent to processes
started with a *creationflags* parameter which includes
``CREATE_NEW_PROCESS_GROUP``.
.. method:: terminate()
Stop the child. On Posix OSs the method sends :py:data:`signal.SIGTERM`
to the child. On Windows the Win32 API function
:c:func:`TerminateProcess` is called to stop the child.
.. method:: wait():
Wait for child process to terminate. Set and return :attr:`returncode`
attribute.
This method is a :ref:`coroutine <coroutine>`.
Example
-------
Implement a function similar to :func:`subprocess.getstatusoutput`, except that
it does not use a shell. Get the output of the "python -m platform" command and
display the output::
import asyncio
import sys
from asyncio import subprocess
@asyncio.coroutine
def getstatusoutput(*args):
proc = yield from asyncio.create_subprocess_exec(
*args,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
try:
stdout, _ = yield from proc.communicate()
except:
proc.kill()
yield from proc.wait()
raise
exitcode = yield from proc.wait()
return (exitcode, stdout)
loop = asyncio.get_event_loop()
coro = getstatusoutput(sys.executable, '-m', 'platform')
exitcode, stdout = loop.run_until_complete(coro)
if not exitcode:
stdout = stdout.decode('ascii').rstrip()
print("Platform: %s" % stdout)
else:
print("Python failed with exit code %s:" % exitcode)
sys.stdout.flush()
sys.stdout.buffer.flush()
sys.stdout.buffer.write(stdout)
sys.stdout.buffer.flush()
loop.close()
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