ParamSpec Question

[max-muoto]

Was curious if anyone had ideas on this.

from typing import Callable, ParamSpec, TypeVar

P = ParamSpec("P")
R = TypeVar("R")


def log_to_database() -> None:
    ...


def add_logging(f: Callable[P, R]) -> Callable[P, R]:
    def inner(*args: P.args, **kwargs: P.kwargs) -> R:
        log_to_database()
        ex = kwargs["test"] 
        print(typing.reveal_type(ex))  # Typed as `builtins .object`
        return f(*args, **kwargs)

    return inner

When using ParamSpec, it seems that values pulled from kwargs are always as typed as object by Pyright and MyPy. Is there any way to provide additional typing information to avoid this? Or is there any reason these aren't just typed as Any?

[erictraut]

The most that a type checker can say about kwargs is that it's a Mapping[str, object]. This is slightly better than Mapping[str, Unknown].

If you're using a ParamSpec, it's dangerous to assume anything about the captured arguments. The arguments are meant to be passed along to a function that is known to accept that signature, so you should generally treat P.args and P.kwargs as a black box.

[max-muoto]

Thanks, makes sense!