为什么asyncio.wait不等待FIRST_COMPLETED

Question

我是Python3.5异步的新手。

在我下面的代码中，asyncio.wait()并不等待stop_future完成：

import asyncio
import datetime
from concurrent.futures import FIRST_COMPLETED


def stop():  # callback after 12 seconds

    print('stop', datetime.datetime.now())
    stop_future.set_result('Done!')


async def display_dt():

    while not stop_future.done():
        print('dt-1', datetime.datetime.now())
        # sleep 5 seconds or stop_future done
        asyncio.wait([await asyncio.sleep(5), stop_future],  return_when=FIRST_COMPLETED)
        print('dt-2', datetime.datetime.now())

    task = asyncio.Task.current_task()
    task.cancel()
    print(stop_future.result())


loop = asyncio.get_event_loop()
stop_future = asyncio.Future()
loop.call_later(12, stop)
loop.run_until_complete(display_dt())
loop.close() 

结果：

dt-1 2015-11-08 00:49:37.324582
dt-2 2015-11-08 00:49:42.325503
dt-1 2015-11-08 00:49:42.325503
dt-2 2015-11-08 00:49:47.326423
dt-1 2015-11-08 00:49:47.326423
stop 2015-11-08 00:49:49.327192  # async.wait stop_future not triggered
dt-2 2015-11-08 00:49:52.327343  # while loop finishes here
>>> Done!

更新：

下面是更新后的函数display_dt的代码，现在asyncio.wait可以工作了。

但我不明白为什么上面的代码与coro不工作?？

@asyncio.coroutine    # decorator necessary? It works fine without 
def display_dt():

    while not stop_future.done():
        print('dt-1', datetime.datetime.now())
        yield from asyncio.wait([asyncio.sleep(5), stop_future], return_when=FIRST_COMPLETED)
        print('dt-2', datetime.datetime.now())

    task = asyncio.Task.current_task()
    task.cancel()
    print(stop_future.result())

结果：

dt-1 2015-11-08 01:19:06.289915
dt-2 2015-11-08 01:19:11.290836
dt-1 2015-11-08 01:19:11.290836
dt-2 2015-11-08 01:19:16.291757
dt-1 2015-11-08 01:19:16.291757
stop 2015-11-08 01:19:18.292525
dt-2 2015-11-08 01:19:18.292525  # async wait stop_future triggered
Done!

更新:需要 @asyncio.coroutine #装饰吗？

我在这伟大的一章上找到了答案

@asyncio.coroutine装饰师并不神奇。实际上，如果它装饰了一个生成器函数，并且没有设置PYTHONASYNCIODEBUG环境变量，那么装饰器实际上什么也不做。为了方便框架的其他部分，它只设置了一个属性_is_coroutine。完全可以用@asyncio.coroutine装饰的裸生成器使用异步。↩。

Answer 1

您必须await .wait()协同线，而不是await您传递给.wait()的协同线。

async def display_dt():

    while not stop_future.done():
        print('dt-1', datetime.datetime.now())
        # sleep 5 seconds or stop_future done
        await asyncio.wait([asyncio.sleep(5), stop_future], return_when=FIRST_COMPLETED) # <----
        print('dt-2', datetime.datetime.now())

    task = asyncio.Task.current_task()
    task.cancel()
    print(stop_future.result())

现在，这相当于编辑，但使用本机协同(即async/await语法)。

更新显示结果：

dt-1 2015-11-08 13:14:21.910399
dt-2 2015-11-08 13:14:26.911320
dt-1 2015-11-08 13:14:26.911320
dt-2 2015-11-08 13:14:31.912240
dt-1 2015-11-08 13:14:31.912240
stop 2015-11-08 13:14:33.913009
dt-2 2015-11-08 13:14:33.913009
Done!