.. currentmodule:: asyncio
On Windows, the default event loop uses :class:`selectors.SelectSelector` which only supports sockets. The :class:`ProactorEventLoop` should be used to support subprocesses. However, the latter does not support SSL.
On Mac OS X older than 10.9 (Mavericks), :class:`selectors.KqueueSelector` does not support character devices like PTY, whereas it is used by the default event loop. The :class:`SelectorEventLoop` can be used with :class:`SelectSelector` or :class:`PollSelector` to handle character devices on Mac OS X 10.6 (Snow Leopard) and later.
.. function:: create_subprocess_shell(cmd, stdin=None, stdout=None, stderr=None, loop=None, limit=None, \*\*kwds) Run the shell command *cmd*. See :meth:`BaseEventLoop.subprocess_shell` for parameters. Return a :class:`~asyncio.subprocess.Process` instance. The optional *limit* parameter sets the buffer limit passed to the :class:`StreamReader`. 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. See :meth:`BaseEventLoop.subprocess_exec` for parameters. Return a :class:`~asyncio.subprocess.Process` instance. The optional *limit* parameter sets the buffer limit passed to the :class:`StreamReader`. This function is a :ref:`coroutine <coroutine>`.
Use the :meth:`BaseEventLoop.connect_read_pipe` and :meth:`BaseEventLoop.connect_write_pipe` methods to connect pipes.
Run subprocesses asynchronously using the :mod:`subprocess` module.
.. method:: BaseEventLoop.subprocess_exec(protocol_factory, \*args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, \*\*kwargs)
Create a subprocess from one or more string arguments (character strings or
bytes strings encoded to the :ref:`filesystem encoding
<filesystem-encoding>`), where the first string
specifies the program to execute, and the remaining strings specify the
program's arguments. (Thus, together the string arguments form the
``sys.argv`` value of the program, assuming it is a Python script.) This is
similar to the standard library :class:`subprocess.Popen` class called with
shell=False and the list of strings passed as the first argument;
however, where :class:`~subprocess.Popen` takes a single argument which is
list of strings, :func:`subprocess_exec` takes multiple string arguments.
Other parameters:
* *stdin*: Either a file-like object representing the pipe to be connected
to the subprocess's standard input stream using
:meth:`~BaseEventLoop.connect_write_pipe`, or the constant
:const:`subprocess.PIPE` (the default). By default a new pipe will be
created and connected.
* *stdout*: Either a file-like object representing the pipe to be connected
to the subprocess's standard output stream using
:meth:`~BaseEventLoop.connect_read_pipe`, or the constant
:const:`subprocess.PIPE` (the default). By default a new pipe will be
created and connected.
* *stderr*: Either a file-like object representing the pipe to be connected
to the subprocess's standard error stream using
:meth:`~BaseEventLoop.connect_read_pipe`, or one of the constants
:const:`subprocess.PIPE` (the default) or :const:`subprocess.STDOUT`.
By default a new pipe will be created and connected. When
:const:`subprocess.STDOUT` is specified, the subprocess's standard error
stream will be connected to the same pipe as the standard output stream.
* All other keyword arguments are passed to :class:`subprocess.Popen`
without interpretation, except for *bufsize*, *universal_newlines* and
*shell*, which should not be specified at all.
Returns a pair of ``(transport, protocol)``, where *transport* is an
instance of :class:`BaseSubprocessTransport`.
This method is a :ref:`coroutine <coroutine>`.
See the constructor of the :class:`subprocess.Popen` class for parameters.
.. method:: BaseEventLoop.subprocess_shell(protocol_factory, cmd, \*, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, \*\*kwargs) Create a subprocess from *cmd*, which is a character string or a bytes string encoded to the :ref:`filesystem encoding <filesystem-encoding>`, using the platform's "shell" syntax. This is similar to the standard library :class:`subprocess.Popen` class called with ``shell=True``. See :meth:`~BaseEventLoop.subprocess_exec` for more details about the remaining arguments. Returns a pair of ``(transport, protocol)``, where *transport* is an instance of :class:`BaseSubprocessTransport`. This method is a :ref:`coroutine <coroutine>`. See the constructor of the :class:`subprocess.Popen` class for parameters.
.. seealso:: The :meth:`BaseEventLoop.connect_read_pipe` and :meth:`BaseEventLoop.connect_write_pipe` methods.
.. 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.
.. 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>`.
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 os
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)
if os.name == 'nt':
loop = asyncio.ProactorEventLoop()
asyncio.set_event_loop(loop)
else:
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, flush=True)
sys.stdout.buffer.write(stdout)
sys.stdout.buffer.flush()
loop.close()