osrf_pycommon.process_utils.async_execute_process_asyncio package

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async osrf_pycommon.process_utils.async_execute_process_asyncio.async_execute_process(protocol_class, cmd=None, cwd=None, env=None, shell=False, emulate_tty=False, stderr_to_stdout=True)

Coroutine to execute a subprocess and yield the output back asynchronously.

This function is meant to be used with the Python asyncio module, which is available in Python 3.5 or greater.

Here is an example of how to use this function:

import asyncio
from osrf_pycommon.process_utils import async_execute_process
from osrf_pycommon.process_utils import AsyncSubprocessProtocol
from osrf_pycommon.process_utils import get_loop


async def setup():
    transport, protocol = await async_execute_process(
        AsyncSubprocessProtocol, ['ls', '/usr'])
    returncode = await protocol.complete
    return returncode

retcode = get_loop().run_until_complete(setup())
get_loop().close()

Tthe first argument is the default AsyncSubprocessProtocol protocol class, which simply prints output from stdout to stdout and output from stderr to stderr.

If you want to capture and do something with the output or write to the stdin, then you need to subclass from the AsyncSubprocessProtocol class, and override the on_stdout_received, on_stderr_received, and on_process_exited functions.

See the documentation for the AsyncSubprocessProtocol class for more details, but here is an example which uses asyncio from Python 3.5:

import asyncio
from osrf_pycommon.process_utils import async_execute_process
from osrf_pycommon.process_utils import AsyncSubprocessProtocol
from osrf_pycommon.process_utils import get_loop


class MyProtocol(AsyncSubprocessProtocol):
    def __init__(self, file_name, **kwargs):
        self.fh = open(file_name, 'w')
        AsyncSubprocessProtocol.__init__(self, **kwargs)

    def on_stdout_received(self, data):
        # Data has line endings intact, but is bytes in Python 3
        self.fh.write(data.decode('utf-8'))

    def on_stderr_received(self, data):
        self.fh.write(data.decode('utf-8'))

    def on_process_exited(self, returncode):
        self.fh.write("Exited with return code: {0}".format(returncode))
        self.fh.close()


async def log_command_to_file(cmd, file_name):

    def create_protocol(**kwargs):
        return MyProtocol(file_name, **kwargs)

    transport, protocol = await async_execute_process(
        create_protocol, cmd)
    returncode = await protocol.complete
    return returncode

get_loop().run_until_complete(
    log_command_to_file(['ls', '/'], '/tmp/out.txt'))
get_loop().close()

See the subprocess.Popen class for more details on some of the parameters to this function like cwd, env, and shell.

See the osrf_pycommon.process_utils.execute_process() function for more details on the emulate_tty parameter.

Parameters:

  • protocol_class (AsyncSubprocessProtocol or a subclass) – Protocol class which handles subprocess callbacks

  • cmd (list) – list of arguments where the executable is the first item

  • cwd (str) – directory in which to run the command

  • env (dict) – a dictionary of environment variable names to values

  • shell (bool) – if True, the cmd variable is interpreted by a the shell

  • emulate_tty (bool) – if True, pty’s are passed to the subprocess for stdout and stderr, see osrf_pycommon.process_utils.execute_process().

  • stderr_to_stdout (bool) – if True, stderr is directed to stdout, so they are not captured separately.

osrf_pycommon.process_utils.async_execute_process_asyncio.get_loop()

This function will return the proper event loop for the subprocess async calls.

On Unix this just returns asyncio.get_event_loop(), but on Windows it will set and return a asyncio.ProactorEventLoop instead.