python 3 asyncio：使用 run_until_complete(asyncio.wait(corutines_list)) 的协程执行顺序

Question

我有一个可能很无用的问题，但我觉得我错过了一些可能对理解 asyncio 工作原理很重要的东西。

我刚开始熟悉 asyncio，并编写了这段非常基本的代码：

import asyncio
import datetime
from random import randint


async def coroutine(i):
    start = datetime.datetime.now()
    print('coroutine {} started.'.format(i))
    n = randint(1, 11)
    await asyncio.sleep(n)
    end = datetime.datetime.now()
    print('coroutine {} finished after {} with random = {}.'.format(i, (end-start).seconds, n))
    return i


def simple():
    loop = asyncio.get_event_loop()
    cors = [coroutine(x) for x in range(20)]
    loop.run_until_complete(asyncio.wait(cors))


if __name__ == '__main__':
    simple()

这是我得到的一个结果：

coroutine 3 started.
coroutine 9 started.
coroutine 15 started.
coroutine 4 started.
coroutine 10 started.
coroutine 16 started.
coroutine 1 started.
coroutine 5 started.
coroutine 11 started.
coroutine 17 started.
coroutine 2 started.
coroutine 6 started.
coroutine 12 started.
coroutine 18 started.
coroutine 0 started.
coroutine 7 started.
coroutine 13 started.
coroutine 19 started.
coroutine 8 started.
coroutine 14 started.
coroutine 7 finished after 1 with random = 1.
coroutine 12 finished after 2 with random = 2.
coroutine 3 finished after 3 with random = 3.
coroutine 5 finished after 3 with random = 3.
coroutine 0 finished after 3 with random = 3.
coroutine 10 finished after 4 with random = 4.
coroutine 17 finished after 4 with random = 4.
coroutine 2 finished after 5 with random = 5.
coroutine 16 finished after 6 with random = 6.
coroutine 18 finished after 6 with random = 6.
coroutine 15 finished after 7 with random = 7.
coroutine 9 finished after 8 with random = 8.
coroutine 1 finished after 8 with random = 8.
coroutine 6 finished after 8 with random = 8.
coroutine 11 finished after 9 with random = 9.
coroutine 8 finished after 9 with random = 9.
coroutine 4 finished after 10 with random = 10.
coroutine 13 finished after 10 with random = 10.
coroutine 19 finished after 10 with random = 10.
coroutine 14 finished after 10 with random = 10.

现在，我的问题是：为什么协程以乱序开始？ 我期待看到一个有序的“协程 x 开始”消息，从协程 0 到协程 20……直到那时我才认为他们会因为随机的睡眠时间而争吵……我错过了什么？

Answer 1

.wait() 规范无法确定该顺序。

你不应该关心它。

实际上所有的协程都是在同一个循环迭代中启动的，几乎是在同一时间。