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

I guess to use high-level api:

proc = yield from asyncio.create_subprocess_exec(
    'python', '-c', 'print(\'Hello async world!\')')

stdout, stderr = yield from proc.communicate()

retcode = proc.returncode

Also you can do more:

yield from proc.stdin.write(b'data')
yield from proc.stdin.drain()

stdout = yield from proc.stdout.read()
stderr = yield from proc.stderr.read()

retcode = yield from proc.wait()

and so on.

But, please, keep in mind that waiting for, say, stdout when child process prints nothing can hang you coroutine.