[cpython 3.9] Decorating a classmethod doesn't work

[daviddavis]

It appears that alru_cache does not seem to work for classmethods. Here's a contrived example.

import asyncio

from async_lru import alru_cache


class Incrementer:
    inc = 1

    @classmethod
    @alru_cache
    async def increment(cls, num):
        return cls.inc + num


async def main():
    print(await Incrementer.increment(5))

asyncio.run(main())

Error:

TypeError: increment() missing 1 required positional argument: 'num'

I would expect it to work since lru_cache works for classmethods.

[Dreamsorcerer]

Umm, when I run your example, the output is:

6

I don't see any errors.

[Dreamsorcerer]

Appears to be a problem with Python 3.9: #512 A little odd, because it works correctly in 3.8, 3.10, 3.11 and 3.12...

[Dreamsorcerer]

I don't have any time to look into this, so feel free to debug and come up with a fix, or just move to another version of Python.

[Dreamsorcerer]

It even works on Pypy 3.9, so it's only cpython 3.9 that fails...

Judging by the codecov change, it would appear to be this code which should be run with a classmethod and makes it work normally: https://github.com/aio-libs/async-lru/blob/565711c9b2740d522e1a0852205a63a54aa216ab/async_lru/init.py#L232-L233

[wangyuhuiever]

I occur this error early today, and I'm sure alru_cache is available when async-lru version < 2.0.0.

class Incrementer:
    inc = 1

    @classmethod
    @alru_cache
    async def increment(cls, num):
        return cls.inc + num

[Dreamsorcerer]

Response is still the same as above. Either debug and come up with a fix or stop using cpython 3.9. We'll stop supporting 3.9 next year anyway, so it's unlikely we'll look into this.