Python 3 hint for decorator

Question

Match the following code:

from typing import Callable, Any

TFunc = Callable[..., Any]

def get_authenticated_user(): return "John"

def require_auth() -> Callable[TFunc, TFunc]:
    def decorator(func: TFunc) -> TFunc:
        def wrapper(*args, **kwargs) -> Any:
            user = get_authenticated_user()
            if user is None:
                raise Exception("Don't!")
            return func(*args, **kwargs)
        return wrapper
    return decorator

@require_auth()
def foo(a: int) -> bool:
    return bool(a % 2)

foo(2)      # Type check OK
foo("no!")  # Type check failing as intended

This piece of code works as intended. Now imagine that I want to extend this, and instead of just executing, func(*args, **kwargs)I want to enter the username in the arguments. Therefore, I am changing the signature of the function.

from typing import Callable, Any

TFunc = Callable[..., Any]

def get_authenticated_user(): return "John"

def inject_user() -> Callable[TFunc, TFunc]:
    def decorator(func: TFunc) -> TFunc:
        def wrapper(*args, **kwargs) -> Any:
            user = get_authenticated_user()
            if user is None:
                raise Exception("Don't!")
            return func(*args, user, **kwargs)  # <- call signature modified

        return wrapper

    return decorator


@inject_user()
def foo(a: int, username: str) -> bool:
    print(username)
    return bool(a % 2)


foo(2)      # Type check OK
foo("no!")  # Type check OK <---- UNEXPECTED

I cannot find the right way to introduce this. I know that in this example the decorated function and the returned function must technically have the same signature (but even this was not found).

Answer 1

Callable, - ; . - , Callable Callable.

typevar:

RT = TypeVar('RT')  # return type

def inject_user() -> Callable[[Callable[..., RT]], Callable[..., RT]]:
    def decorator(func: Callable[..., RT]) -> Callable[..., RT]:
        def wrapper(*args, **kwargs) -> RT:
            # ...

foo() def (*Any, **Any) -> builtins.bool* reveal_type().

, Callable , . .

• : Callable,
• TypeVar ,

. - , usecase, , :

- . .