async singledispatch not retried

[thebuchanan3]

async functools.singledispatch or functools.singledispatchmethod decorated functions are not retried using tenacity:

import asyncio
import tenacity

from functools import singledispatch

@tenacity.retry(
    retry=tenacity.retry_if_exception_type(RuntimeError),
    stop=tenacity.stop_after_attempt(2),
)
@singledispatch
async def foo(a: str):
    raise RuntimeError()


asyncio.run(foo("test"))  # RuntimeError

The example is not retried and raises RuntimeError instead of tenacity.RetryError.

The reason is that inspect.iscoroutinefunction is used under the hood, which produces false negatives for singledispatch functions and methods.

from functools import singledispatch
from inspect import iscoroutinefunction

@singledispatch
async def foo(a: str):
    raise RuntimeError()


assert iscoroutinefunction(foo)  # AssertionError