Is there a way to properly annotate decorators for both functions and methods?

[lonelyenvoy]

I opened an issue about method decorators previously and it was transferred to python/mypy. Although it looks like an implementation issue in mypy, it's indeed related to the design of the typing.

For now, it seems impossible to annotate decorators that can be applied to both functions outside and inside classes (i.e. methods). Is there a workaround?

def decorator(func):
    def wrapper(*args, **kwargs):
        ...
    return wrapper

@decorator
def foo(arg):
    ... 

class A:
    @decorator
    def bar(self, arg):
        ...

[gvanrossum]

Still seems a mypy issue. It conflates class and instance methods.

[lonelyenvoy]

Still seems a mypy issue. It conflates class and instance methods.

@gvanrossum Can you please elaborate a little bit by commenting in the mypy issue so that they can fix it? Thank you.

[gvanrossum]

Not right now, I am about to head on vacation. All I know is that this is a longstanding mypy issue.

[lonelyenvoy]

OK, enjoy your vacation time.

[Tomaz-Vieira]

I tried it with pyright and things seem to check just right:

# pyright: strict

from typing import Callable, TypeVar
from typing_extensions import ParamSpec


_P = ParamSpec("_P")
_OUT = TypeVar("_OUT")

def decorator(func: Callable[_P, _OUT]) -> Callable[_P, _OUT]:
    def wrapper(*args: _P.args, **kwargs: _P.kwargs) -> _OUT:
        print(f"caling {func.__name__}")
        return func(*args, **kwargs)
    return wrapper

@decorator
def foo(arg: int) -> int:
    return 123

reveal_type(foo) # (arg: int) -> int

class A:
    @decorator
    def bar(self, arg: str) -> None:
        return None

reveal_type(A().bar) # (arg: str) -> None

so I'd say there is a way to properly annotate decorators for both functions and methods. But I think mypy doesn't support ParamSpec yet

[srittau]

I am closing this here as this seems to be a mypy issue (python/mypy#10805).