foo.py

import asyncio
import os
from pprint import pprint


async def do_work():
    """Schedule and run a bunch of tasks that do nothing but sleep"""
    tasks = [asyncio.create_task(asyncio.sleep(duration)) for duration in [0, 1, 3, 5]]
    results, _ = await asyncio.wait(tasks)
    return results


def main():
    try:
        # If there is an existing event loop, schedule the coroutine do_work on
        # it and return its result.
        loop = asyncio.get_running_loop()
        results = asyncio.run_coroutine_threadsafe(do_work, loop).result()
    except RuntimeError:
        # Otherwise, start a new event loop ourselves.
        results = asyncio.run(do_work())
    pprint(results)


if __name__ == "__main__":
    if os.environ["RUN_ASYNC"].lower() == "true":
        print("Running asynchronously")
        loop = asyncio.new_event_loop()
        main()
        # This will run forever because there's no (easy) way to signal the
        # tasks scheduled in main() have actually run and completed, but for
        # demo purposes, this is fine.
        loop.run_forever()
    else:
        print("Running synchronously")
        main()

output.txt

➔  export RUN_ASYNC=false; time python foo.py
Running synchronously
{<Task finished name='Task-2' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>,
 <Task finished name='Task-3' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>,
 <Task finished name='Task-4' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>,
 <Task finished name='Task-5' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>}
python foo.py  0.05s user 0.00s system 0% cpu 5.050 total


➔  export RUN_ASYNC=true; time python foo.py
Running asynchronously
{<Task finished name='Task-2' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>,
 <Task finished name='Task-3' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>,
 <Task finished name='Task-4' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>,
 <Task finished name='Task-5' coro=<sleep() done, defined at /usr/lib/python3.9/asyncio/tasks.py:636> result=None>}


^CTraceback (most recent call last):
  File "/home/zoni/Workspace/castoredc/castoredc-api-review/foo.py", line 33, in <module>
    loop.run_forever()
  File "/usr/lib/python3.9/asyncio/base_events.py", line 596, in run_forever
    self._run_once()
  File "/usr/lib/python3.9/asyncio/base_events.py", line 1854, in _run_once
    event_list = self._selector.select(timeout)
  File "/usr/lib/python3.9/selectors.py", line 469, in select
    fd_event_list = self._selector.poll(timeout, max_ev)
KeyboardInterrupt

python foo.py  0.10s user 0.00s system 1% cpu 6.820 total