createpipedprocesses.py

async def create_piped_processes(
        *cmds, stdin = asyncio.subprocess.DEVNULL, stdout = None):
    if stdout is None:
        out, w = os.pipe()
    else:
        out = None
        w = stdout
    p = []
    for ii, c in reversed(tuple(enumerate(cmds))):
        if ii == 0:
            i = stdin
        else:
            i, o = os.pipe()

        p.append(await asyncio.subprocess.create_subprocess_exec(
            *c, stdout = w, stdin = i))
        os.close(w)
        if ii > 0:
            os.close(i)
        w = o
    return out, map(lambda p: p.wait(), p)

'''
    Usage:
    fd, procs = await create_piped_processes(
        ['xzcat', out.name],
        ['restore', '-t', '-f', '-'])
    for line in os.read(fd, 1024).decode('utf-8').splitlines():
        ...
    os.close(fd)
    status = await asyncio.gather(*procs)
'''