The current code example contains [1]:

    print("Python failed with exit code %s:" % exitcode)
    sys.stdout.flush()
    sys.stdout.buffer.flush()
    sys.stdout.buffer.write(stdout)
    sys.stdout.buffer.flush()

that looks bizarre.

Either a comment should be added that explains why the `.flush()` calls
are necessary or they should be removed.

I've attached the documentation patch that removes the calls.

[1] http://hg.python.org/cpython/file/2af5a52b9b87/Doc/library/asyncio-subprocess.rst#l227