Decorator that calc the last execution time of a function. The result is added as a new function attribute named 'last_execution_time'.

last_execution_time.py

import time
import functools

def timer_decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time_ns()
        res = func(*args, **kwargs)
        end = time.time_ns()
        wrapper.last_execution_time = end - start
        return res
    return wrapper


if __name__ == "__main__":

    @timer_decorator
    def fact(n: int) -> int:
        res = 1
        for i in range(2, n+1):
            res *= i
        return res
    
    
    N = 100000
    fact_N = fact(N)
    print(f"Calculated fact({N}) in {fact.last_execution_time/1000000} ms.")