Python asyncio sleep not wakes up

Question

I am trying yo have a progress indicator where one task is doing something while the other indicates a progress. My hello world version of this things goes to sleep in one of the tasks but never wakes up.

What am I missing?

Thanks a lot

import asyncio
import sys
import time
import itertools


progress = True


def get_progress():
    return progress


async def define_progress():
    print("progress started")
    await asyncio.sleep(2)
    progress = False
    print("progress ended")


async def run_spinner(msg):
    spinner = itertools.cycle(['-', '/', '|', '\\'])
    sys.stdout.write("{0} ".format(msg))
    while(get_progress()):
        sys.stdout.write("{0}".format(next(spinner)))
        sys.stdout.flush()
        time.sleep(0.3)
        sys.stdout.write('\b')


async def main():
    msg = "start logic"
    await asyncio.gather(run_spinner(msg), define_progress())


loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(main())
finally:
    loop.close()

The output looks like below while the second line infinitely run the spinner.

progress started
creating package\

Answer 1

I had to make progress a global variable and add await asyncio.sleep(1) to run_spinner. I'm not sure this answers your question, but it does seem to do what you wanted.

import asyncio
import sys
import time
import itertools

global progress

progress = True



def get_progress():
    global progress
    return progress

async def define_progress():
    global progress
    print("progress started")
    await asyncio.sleep(2)
    progress = False
    print("progress ended")


async def run_spinner(msg):
    spinner = itertools.cycle(['-', '/', '|', '\\'])
    sys.stdout.write("{0} ".format(msg))
    while(get_progress()):
        sys.stdout.write("{0}".format(next(spinner)))
        sys.stdout.flush()
        time.sleep(0.2)
        sys.stdout.write('\b')
        await asyncio.sleep(1)


async def main():
    msg = "start logic"
    await asyncio.gather(run_spinner(msg), define_progress())


loop = asyncio.get_event_loop()
try:
    loop.run_until_complete(main())
finally:
    loop.close()

Answer 2

1. The run_spinner coroutine is missing an await asyncio.sleep(0) to give the other task define_progress some processing time.
2. The progress = False instruction in the define_progress task creates a local variable which shadows the global variable of the same name. Therefor, even if the define_progress finishes, the run_spinner will continue as it reads the global which is still True.

Remarks: From https://docs.python.org/3.9/library/asyncio-task.html#sleeping

sleep() always suspends the current task, allowing other tasks to run.

Setting the delay to 0 provides an optimized path to allow other tasks to run. This can be used by long-running functions to avoid blocking the event loop for the full duration of the function call.