import functools


def debug(func):
    """Print the function signature and return value"""

    @functools.wraps(func)
    def wrapper_debug(*args, **kwargs):
        args_repr = [repr(a) for a in args]  # 1
        kwargs_repr = [f"{k}={v!r}" for k, v in kwargs.items()]  # 2
        signature = ", ".join(args_repr + kwargs_repr)  # 3
        print(f"Calling {func.__name__}({signature})")
        value = func(*args, **kwargs)
        print(f"{func.__name__!r} returned {value!r}")  # 4
        return value

    return wrapper_debug


@debug
def make_greeting(name, age=None):
    if age is None:
        return f"Howdy {name}!"
    else:
        return f"Whoa {name}! {age} already, you are growing up!"


make_greeting("Benjamin")

make_greeting("Richard", age=112)

make_greeting(name="Dorrisile", age=116)


import math

# Apply a decorator to a standard library function
math.factorial = debug(math.factorial)

# The approximation of e
def approximate_e(terms=18):
    return sum(1 / math.factorial(n) for n in range(terms))


approximate_e(5)