Asyncio wait_for can be foiled by blocking code

good-timeout.py

import asyncio

async def eternity():
    await asyncio.sleep(2)  # Sleep asynchronously
    print("I should've timed out")

async def main():
    # Wait for at most 1 second
    try:
        await asyncio.wait_for(eternity(), timeout=1.0)
    except asyncio.TimeoutError:
        print("timeout!")

asyncio.run(main())

# Will print "timeout!" after 1 second

naughty-blocker.py

import asyncio
import time

async def eternity():
    time.sleep(2)  # Sleep in a blocking way
    print("I should've timed out")

async def main():
    # Wait for at most 1 second
    try:
        await asyncio.wait_for(eternity(), timeout=1.0)
    except asyncio.TimeoutError:
        print("timeout!")

asyncio.run(main())

# Will print "I should've timed out" after two seconds despite the timout

That's actually a feature. Time is a built-in module that's made in C, which has the function as you know it, sleep. The entire idea behind the sleep function is to hault the entire program execution for a duration of time, before once again allowing it to go on as usual. This isn't an issue with Asyncio or Python. It's nothing more than a feature.

If you're curious, check out the source code behind the time module - https://github.com/python/cpython/blob/main/Modules/timemodule.c#L360