How to Truly Achieve 'Fire and Forget' with Python's Async/Await?

"Fire and Forget" with Python's Async/Await

In Python's async/await syntax, executing an asynchronous function without awaiting it doesn't achieve the desired "fire and forget" effect. Instead, the program exits with a runtime warning.

asyncio.Task for "Fire and Forget"

To implement "fire and forget" in asyncio, use asyncio.Task to create a task that performs the desired operation in the background. By invoking asyncio.ensure_future(async_foo()), the task associated with async_foo() is started and does not wait for its completion. This is a simple yet effective approach for asynchronous operations that don't require being explicitly awaited.

async def async_foo():
    print("Async foo started")
    await asyncio.sleep(1)
    print("Async foo done")


async def main():
    asyncio.ensure_future(async_foo())  # Fire and forget async_foo()

Completing Pending Tasks

Note that tasks created using asyncio.Task are expected to be completed before the event loop finishes. If tasks remain pending, a warning will be generated. To prevent this, explicitly await all pending tasks once the event loop completes.

async def main():
    asyncio.ensure_future(async_foo())  # Fire and forget async_foo()

    loop = asyncio.get_event_loop()
    await asyncio.gather(*asyncio.Task.all_tasks())

Cancelling Tasks Instead of Awaiting

Alternatively, if you don't want to await certain tasks indefinitely, you can cancel them:

async def echo_forever():
    while True:
        print("Echo")
        await asyncio.sleep(1)


async def main():
    asyncio.ensure_future(echo_forever())  # Fire and forget echo_forever()

    loop = asyncio.get_event_loop()
    for task in asyncio.Task.all_tasks():
        task.cancel()
        with suppress(asyncio.CancelledError):
            await task

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