import sys
import asyncio

@asyncio.coroutine
def long_sleep_subprocess():
    args = [sys.executable, '-c', 'import time; time.sleep(20)']
    proc = yield from asyncio.create_subprocess_exec(*args)
    try:
        yield from proc.wait()
    except asyncio.CancelledError:
        proc.terminate()

@asyncio.coroutine
def fast_sleep():
    yield from asyncio.sleep(.500)
    long_sleep_task.cancel()

@asyncio.coroutine
def cancel_after_first_completed(tasks):
    while tasks:
        done, pending = yield from asyncio.wait(tasks,
                            return_when=asyncio.FIRST_COMPLETED)
        for task in done:
            tasks.remove(task)
        for task in pending:
            task.cancel()

loop = asyncio.get_event_loop()
loop.set_debug(True)
long_sleep_task = asyncio.Task(long_sleep_subprocess())
tasks = [asyncio.Task(fast_sleep()),
         long_sleep_task,
         asyncio.Task(asyncio.sleep(10)), # No exception when this task is not in the list.
         ]
main_task = asyncio.Task(cancel_after_first_completed(tasks))
loop.run_until_complete(main_task)
loop.close()