为什么asyncio.wait不会等待FIRST_COMPLETED

Question

我刚接触Python 3.5 asyncio。

在asyncio.wait我下面的代码（）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：

下面是更新函数display_dt的代码。现在asyncio.wait工作正常。
但我不明白为什么上面的代码与科罗不起作用??

@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：必要 @ asyncio.coroutine＃设计师吗？

我找到了答案在this great chapter：

的@ asyncio.coroutine装饰并不神奇。事实上，如果它装饰一个生成器函数并且PYTHONASYNCIODEBUG环境变量没有被设置，那么装饰器几乎不会做任何事情。它只是为了框架的其他部分设置一个属性_is_coroutine。它可以在all.↩

Answer 1

与不饰@ asyncio.coroutine裸发电机使用ASYNCIO必须await的.wait()协程，不await的协程，你传球.wait()：

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()) 

现在这相当于您的编辑，但使用本地协程（即async/await语法）。

更新表示结果：

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!