How to stream stdout/stderr from a child process using asyncio, and obtain its exit code after?

Question

Under Python 3.4 on Windows, I need to stream data written to stdout/stderr by a child process, i.e. receive its output as it occurs, using the asyncio framework introduced

Answer 1

Since the event loop may see and notify the process exit before reading the remaining data for stdout/stderr, we need to check PIPE close events in addition to the process exit event.

This is a correction for aknuds1 answer:

class SubprocessProtocol(asyncio.SubprocessProtocol):
    def __init__(self):
        self._exited = False
        self._closed_stdout = False
        self._closed_stderr = False

    @property
    def finished(self):
        return self._exited and self._closed_stdout and self._closed_stderr

    def signal_exit(self):
        if not self.finished:
            return
        loop.stop()        

    def pipe_data_received(self, fd, data):
        if fd == 1:
            name = 'stdout'
        elif fd == 2:
            name = 'stderr'
        text = data.decode(locale.getpreferredencoding(False))
        print('Received from {}: {}'.format(name, text.strip()))

    def pipe_connection_lost(self, fd, exc):
        if fd == 1:
            self._closed_stdout = True
        elif fd == 2:
            self._closed_stderr = True
        self.signal_exit()

    def process_exited(self):
        self._exited = True
        self.signal_exit()