python 3 asyncio: coroutines execution order using run_until_complete(asyncio.wait(corutines_list))

问题

I have what is probably a quite useless question, but nevertheless I feel I am missing something that might be important to understand how asyncio works.

I just started to familiarize with asyncio and I wrote this very basic piece of code:

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()

This is one result I got:

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.

Now, my question is: why on earth the coroutines start in a scrambled order? I was expecting to see an ordered "coroutine x started" message, from coroutine 0 to coroutine 20...only then I assumed they would scramble due to the randomized sleep time...what am I missing?

回答1:

The order is undetermenistic by .wait() specification.

You shouldn't care about it.

Actually all coroutines are started at the same loop iteration, almost at the same time.

来源：https://stackoverflow.com/questions/40635110/python-3-asyncio-coroutines-execution-order-using-run-until-completeasyncio-wa

标签

python-3.5

python-asyncio

coroutine