How to Implement 'Fire and Forget' Asynchronous Operations in Python Async/Await?

"Fire and Forget" in Python Async/Await

In certain scenarios, there is a need to initiate an asynchronous operation that doesn't require waiting for its completion. Traditionally, the "fire and forget" approach in Tornado's coroutines could be achieved by omitting the yield keyword.

In Python 3.5's async/await syntax, however, such an implementation raises a RuntimeWarning, indicating that the coroutine was never awaited.

Asyncio.Task: The Solution

Fortunately, Python's asyncio library provides a solution through its asyncio.Task class. This allows the creation of a task that can execute in the background, without blocking the main execution.

import asyncio

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()

    # continue with other actions

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

This approach ensures that async_foo() is executed asynchronously while other actions can continue without waiting.

Handling Pending Tasks

It's important to note that when the event loop completes, asyncio expects all tasks to be finished. As such, any remaining pending tasks can result in warnings. To prevent this, one can either await all pending tasks or cancel them.

Option 1: Await Pending Tasks

pending = asyncio.Task.all_tasks()
loop.run_until_complete(asyncio.gather(*pending))

Option 2: Cancel Pending Tasks

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

By canceling the tasks, they are removed from the event loop's schedule, preventing any potential warnings.

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