Detect asyncio-dangling-task (RUF006) when discarding return value

[tjkuson]

import asyncio

for i in range(10):
    asyncio.create_task(foo)

triggers asyncio-dangling-task but

import asyncio

for i in range(10):
    _ = asyncio.create_task(foo)

does not.

I would expect Ruff to trigger asyncio-dangling-task when the return value of asyncio.create_task is discarded, following the rationale of the rule.

[zanieb]

This seems reasonable to me!

[allaboutevemirolive]

Hye, @tjkuson

Minimizing

I'm new to Ruff's contributions. I try to duplicate your issue by compiling Ruff using cargo build --release and running the command on a Python file.

./ruff check /home/nemesis/Documents/Github/test/python/game.py

game.py:

import asyncio


async def some_coro(param):
    print(f"Executing coroutine with param: {param}")
    await asyncio.sleep(1)
    print(f"Coroutine with param {param} completed")


async def main():
    for i in range(10):
        asyncio.create_task(some_coro(param=i))


if __name__ == "__main__":
    asyncio.run(main())

I expected it would produce an error: asyncio-dangling-task, like you mentioned above, but it didn't.

The result is also the same for this snippet.

_ = asyncio.create_task(some_coro(param=i))

Python Version:

$ python3 --version
Python 3.12.0

Local Machine:

Release 11 (bullseye) 64-bit
Kernel Linux 5.10.0-26-amd64 x86_64
Memory: 7.5 GiB
Processor: Intel® Core™ i5-8250U CPU @ 1.60GHz × 8 
Graphics: Mesa Intel® UHD Graphics 620 (KBL GT2)

Edit:

The rule is disabled by default. Use:

./ruff check --select RUF006 [PATH]

[MichaReiser]

I'm not sure if this behavior is intentional, similar to that ruff allows _ variables to be unused. @charliermarsh was it an intentional decision to not raise the lint for variables starting with _?

[charliermarsh]

@MichaReiser - Not intentional -- this rule doesn't look at assignments, it only looks at standalone expressions that include asyncio.create_task(...), and then assumes that those are dangling by virtue of being a standalone expression statement.

[tjkuson]

@allaboutevemirolive I think you need to select the rule (it isn't enabled by default) using --select RUF006.

[asafamr-mm]

Hi,I gave it a try.
I'm new to rust (and the project codebase) and would love feedback. What do you think?

[charliermarsh]

Thanks @asafamr-mm!