[Python] Typing a callable with ParamSpec or no args (`Callable[P, Any] | Callable[[], Any]`)

Here's a decorator that accepts a callable (fn: Callable[P, Any]) with the same signature as the function getting wrapped. It works and type checks.

import inspect
from typing import Any, Callable, ParamSpec, TypeVar, Union

P = ParamSpec("P")
T = TypeVar("T")


def deco1(fn: Callable[P, Any]) -> Callable[[Callable[P, T]], Callable[P, T]]:
def decorator(wrapped_fn: Callable[P, T]) -> Callable[P, T]:
def inner(*args: P.args, **kwargs: P.kwargs) -> T:
fn(*args, **kwargs)
return wrapped_fn(*args, **kwargs)

return inner

return decorator


def logger1(x: int, y: str) -> None:
print(f"logger1: x={x}, y={y}")


@deco1(logger1)
def wrapped1(x: int, y: str) -> None: ...


wrapped1(1, "test") # prints "logger1: x=1, y=test"


Here's a decorator that accepts a callable (fn: Callable[[], Any]) with no arguments. It also works and type checks.

def deco2(fn: Callable[[], Any]) -> Callable[[Callable[P, T]], Callable[P, T]]:
def decorator(wrapped_fn: Callable[P, T]) -> Callable[P, T]:
def inner(*args: P.args, **kwargs: P.kwargs) -> T:
fn()
return wrapped_fn(*args, **kwargs)

return inner

return decorator


def logger2() -> None:
print(f"logger2")


@deco2(logger2)
def wrapped2(x: int, y: str) -> None: ...


wrapped2(1, "test") # prints "logger2"


I'd like to combine deco1 and deco2 into a single function deco3. The following works at run-time, but I can't get the type checker to pass. Is this possible?

def deco3(
fn: Callable[[], Any] | Callable[P, Any],
) -> Callable[[Callable[P, T]], Callable[P, T]]:
def decorator(wrapped_fn: Callable[P, T]) -> Callable[P, T]:
def inner(*args: P.args, **kwargs: P.kwargs) -> T:
if len(inspect.signature(fn).parameters):
fn(*args, **kwargs)
else:
fn() # pyright error: Arguments for ParamSpec "P@deco3" are missing (reportCallIssue)
return wrapped_fn(*args, **kwargs)

return inner

return decorator


@deco3(logger1)
def wrapped_with_logger1(x: int, y: str) -> None: ...


@deco3(logger2) # pyright error: Argument of type "(x: int, y: str) -> None" cannot be assigned to parameter of type "() -> T@deco3"
def wrapped_with_logger2(x: int, y: str) -> None: ...


wrapped_with_logger1(1, "test") # prints "logger1: x=1, y=test"
wrapped_with_logger2(1, "test") # prints "logger2" but pyright error: Expected 0 positional arguments (reportCallIssue)

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