asyncio-exceptions.py

import asyncio


loop = asyncio.get_event_loop()


async def f1():
    for _ in range(10):
        await asyncio.sleep(1)
    print("task 1 is done")


async def f2():
    for _ in range(3):
        await asyncio.sleep(0.5)
    print("task 2 will raise exception")
    raise RuntimeError("artificial exception")


def main_wait():
    a = asyncio.ensure_future(f1())
    b = asyncio.ensure_future(f2())
    done, pending = loop.run_until_complete(
        asyncio.wait([a, b], return_when=asyncio.FIRST_EXCEPTION)
    )
    print("done", done)
    print("pending", pending)
    try:
        for task in done:
            if task.exception():
                raise task.exception()
    finally:
        for task in pending:
            task.cancel()
            try:
                loop.run_until_complete(task)
            except asyncio.CancelledError:
                pass


if __name__ == "__main__":
    main_wait()