async function in Python not working as expected

user_13476754 0
Viewed 858

I have the following code snippet:

import asyncio

def main():
    asyncio.run(work())
    print("BEFORE")

async def work():
    await asyncio.sleep(1)
    print("AFTER")

main()

I would like "BEFORE" to be printed first, followed by "AFTER" however this prints "AFTER" first instead - have I misunderstood how async functions work? I thought that running asyncio.run(...) would allow my code to skip to print("BEFORE") while still running work() in the background.

Ideal output is:

BEFORE
AFTER

Right now it's

AFTER
BEFORE
async-await asynchronous multithreading python
2 Answers

run seems to be blocking, so you might want to just use gather here:

import asyncio

async def main():
    await asyncio.gather(work(), setup())
    print('After gather')

async def work():
    await asyncio.sleep(2)
    print("AFTER")

async def setup():
    print("BEFORE")

asyncio.run(main())

This correctly prints

BEFORE
AFTER
After gather

The entire gather statement itself is blocking as well, but all of the functions specified in the gather statement can run asynchronously.

user_116598810

According to the documentation:

The asyncio.run() function to run the top-level entry point “main()” function (see the above example.)

The asyncio.run should be the entry point, not used for starting a background job. So it does not skip to print("BEFORE").

user_31343330
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