How does "await" make code flow in Python?

Question

How does "await" make code flow in Python? This is the code to clear my question

import asyncio

async def io_related(name):
    print(f'{name} started')
    await asyncio.sleep(0.1)
    print(f'{name} finished')


async def main():
    await asyncio.gather(
        io_related('1'),
        io_related('2'),
        io_related('3'),
        io_related('4'),
    )

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

and I got this output:

"1 started

2 started

3 started

4 started

1 finished

3 finished

2 finished

4 finished"

Why "3" finished before "2" ?. How does the code flow? I tried putting "1", "2", "3" in the "await asyncio.gather". It works as I expected but after the item "4", the order of things "finished" is messy terribly.

Why is this behavior unexpected? Are you aware of the purpose of asynchronous programming? — Brian61354270
– Brian61354270, Commented Mar 19, 2020 at 0:33

Rashid 'Lee' Ibrahim · Accepted Answer · 2020-03-19 00:35:09Z

2

This is a question about how threading/asynchronous programming works. Async methods will all fire off at the same time, but finish whenever the data gets back.

The await here is just the keyword saying, "hey wait until all these come back before moving on".

So think of it more like loading webpages. If you call up google.com, microsoft.com, netflix.com and stackoverflow.com all at the same time, it can be reasonably expected that they might not return the page in the same order as you called them. That would depend on several things outside the scope of this question.

The key point here is that when you start using asynchronous methods, you cannot expect the results to come back in the order you called them.

answered Mar 19, 2020 at 0:35

Rashid 'Lee' Ibrahim

1,3921 gold badge9 silver badges27 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

T H Over a year ago

Thank you. I got it. It's very helpful

Collectives™ on Stack Overflow

How does "await" make code flow in Python?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related