Python3.x 请解释任务已被 destruct 但未决！取消任务后

问题在于取消任务后立即关闭循环.作为cancel() docs state人

"这将安排通过事件循环将取消的错误抛出到the next cycle上包装的协同程序中."

以这段代码为例:

import asyncio
import signal


async def pending_doom():
    await asyncio.sleep(2)
    print(">> Cancelling tasks now")
    for task in asyncio.Task.all_tasks():
        task.cancel()

    print(">> Done cancelling tasks")
    asyncio.get_event_loop().stop()


def ask_exit():
    for task in asyncio.Task.all_tasks():
        task.cancel()


async def looping_coro():
    print("Executing coroutine")
    while True:
        try:
            await asyncio.sleep(0.25)
        except asyncio.CancelledError:
            print("Got CancelledError")
            break

        print("Done waiting")

    print("Done executing coroutine")
    asyncio.get_event_loop().stop()


def main():
    asyncio.async(pending_doom())
    asyncio.async(looping_coro())

    loop = asyncio.get_event_loop()
    for sig in (signal.SIGINT, signal.SIGTERM):
        loop.add_signal_handler(sig, ask_exit)

    loop.run_forever()

    # I had to manually remove the handlers to
    # avoid an exception on BaseEventLoop.__del__
    for sig in (signal.SIGINT, signal.SIGTERM):
        loop.remove_signal_handler(sig)


if __name__ == '__main__':
    main()

注意，ask_exit取消任务，但不执行循环，在下一个循环中，looping_coro()停止循环.如果取消，则输出为:

Executing coroutine
Done waiting
Done waiting
Done waiting
Done waiting
^CGot CancelledError
Done executing coroutine

请注意pending_doom如何取消和停止循环immediately after.如果你让它一直运行到pending_doom个协同程序从睡眠中醒来，你会看到同样的警告:

Executing coroutine
Done waiting
Done waiting
Done waiting
Done waiting
Done waiting
Done waiting
Done waiting
>> Cancelling tasks now
>> Done cancelling tasks
Task was destroyed but it is pending!
task: <Task pending coro=<looping_coro() running at canceling_coroutines.py:24> wait_for=<Future cancelled>>