How to typehint the return value of a function that takes other functions

Question

I have a function that accepts other functions, and would like to type-hint the return value of this "wrapper" function. The function is similar to this below, but with a lot more logic specific to the use case. That said, this function is also pretty handy:

def guard(func, default: WhatGoesHere = None) -> Optional[WhatGoesHere]:
    try:
        return func()
    except:
        return default

The function is used like this, with existing typehinted functions as well as the occasional lambda:

def difficult_math() -> int:
    return e^(pi * i) / 0

if res := guard(difficult_math):
   ...

if res := guard(lambda: x/3):
   ...

Answer 1

Something like this

from typing import Callable, Optional, TypeVar

R = TypeVar('R')

def guard(func: Callable[[], R], default: R = None) -> Optional[R]:
    try:
        return func()
    except:
        return default

If your function would be taking *args, **kwargs you can extend this with ParamSpec. And additional positional parameters you'd want to include Concatenate.