Side effects of improperly closing an asyncio event loop

1-main.py

import asyncio

USE_ASYNCIO_RUN = False


class ImaginaryResource:
    def __enter__(self):
        print("1. Opening resource")
        return self

    def __exit__(self, exc_type, exc_val, tb):
        print("6. Closing resource")


async def function():
    with ImaginaryResource() as resource:
        try:
            print("2. Working with resource")
            await asyncio.sleep(5)
        finally:
            print("5. Running finally clause")


async def main(loop=None):
    task = asyncio.create_task(function())
    await asyncio.sleep(0.5)

    print("3. Cancelling task")
    task.cancel()

    if loop is not None:
        print("4a. Stopping loop!!!")
        loop.stop()
        # If we yield back to event loop now, main() *will* not finish
        await asyncio.sleep(0)

    print("4b. Exiting main()")


if USE_ASYNCIO_RUN:
    asyncio.run(main())
else:
    loop = asyncio.new_event_loop()
    loop.run_until_complete(main(loop))

2-outputs.py

# Using asyncio.run()
1. Opening resource
2. Working with resource
3. Cancelling task
4. Exiting main()
5. Running finally clause
6. Closing resource

# Using loop.stop()
1. Opening resource
2. Working with resource
3. Cancelling task
4a. Stopping loop!!!
Traceback (most recent call last):
  File "main.py", line 67, in <module>
    loop.run_until_complete(main(loop))
  File "asyncio\base_events.py", line 651, in run_until_complete
    raise RuntimeError('Event loop stopped before Future completed.')
RuntimeError: Event loop stopped before Future completed.