Type checking for *args and **kwargs when passing them to another function

[t1m013y]

Problem:

I am writing a python application, and I made a function that creates an object and passes its additional *args and **kwargs to object's constructor and takes few its own arguments. I want to make *args and **kwargs typed exactly as inner function's arguments.

Description and examples:

A simple example with two functions:

def inner(a: int, b: int) -> None:
    ...


def wrapper(arg1: str, *args, **kwargs) -> None:
    inner(*args, **kwargs)  # It will automatically detect passing arguments to another function

In my case, inner is object constructor, I gave an example with functions to make it more simple.

Type checkers should see wrapper's signature like this:

def wrapper(arg1: str, a: int, b: int):
    ...

It may be enabled by default when passing *args and **kwargs to another function is detected or it may be enabled by adding a decorator to the function.

Detailed description:

Already suggested this to mypy, detailed description of this feature can be found here: python/mypy#19302.

[erictraut]

Here's how that would typically be done.

from typing import Callable, Concatenate

def inner(a: int, b: int) -> None: ...

def create_wrapper[**P, R](fn: Callable[P, R]) -> Callable[Concatenate[str, P], R]:
    def wrapper(arg1: str, *args: P.args, **kwargs: P.kwargs) -> R:
        return fn(*args, **kwargs)

    return wrapper

wrapper = create_wrapper(inner)

[t1m013y]

Here's how that would typically be done.

from typing import Callable, Concatenate

def inner(a: int, b: int) -> None: ...

def create_wrapper[**P, R](fn: Callable[P, R]) -> Callable[Concatenate[str, *P], R]:
def wrapper(arg1: str, *args: P.args, **kwargs: P.kwargs) -> R:
return fn(*args, **kwargs)

return wrapper

wrapper = create_wrapper(inner)

It's too difficult, need to create a single-use decorator with complex typing. My feature is about an easy way to do this (automatically detected passing arguments to another function or by just adding a decorator to a wrapper).