envoi.py

import asyncio
import shlex


# inspired by https://docs.python.org/3/library/asyncio-subprocess.html

class CheckOutput(asyncio.SubprocessProtocol):
    def __init__(self, exit_future):
        self.exit_future = exit_future
        self.output = bytearray()

    def pipe_data_received(self, fd, data):
        self.output.extend(data)

    def process_exited(self):
        self.exit_future.set_result(True)


@asyncio.coroutine
def check_output(command):
    command = shlex.split(command)
    loop = asyncio.get_event_loop()
    exit_future = asyncio.Future()

    # Create the subprocess controlled by the protocol DateProtocol,
    # redirect the standard output into a pipe
    create = loop.subprocess_exec(
        lambda: CheckOutput(exit_future),
        *command,
        stdin=None,
        stderr=None
    )
    transport, protocol = yield from create

    # Wait for the subprocess exit using the process_exited() method
    # of the protocol
    yield from exit_future

    # Close the stdout pipe
    transport.close()

    # Read the output which was collected by the pipe_data_received()
    # method of the protocol
    data = bytes(protocol.output)
    return data.decode('utf-8').rstrip()


if __name__ == '__main__': 
    loop = asyncio.get_event_loop()
    command = """date --date='TZ="America/Martinique" 09:00 next Fri'"""
    date = loop.run_until_complete(check_output(command))
    print("Command output: %s" % date)
    loop.close()