python 装饰器不返回 function 值

Question

I'm starting with decorators so I tried a basic example a debug decorator where it prints function name, input arguments and output value. The below is my debug decorator.

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

Getting the factorial of each number and at the end sum of all these factorials I wanted. Unable to get the sum of factorials. ie the debug decorator is not returning the original function value.

from decorator import debug
import math

math.factorial = debug(math.factorial)

def approximate_e(terms=18):
    return sum(1 / math.factorial(n) for n in range(terms))

approximate_e(5)

This is the output I'm getting when I run the code

Calling factorial(0)
'factorial' returned 1
Calling factorial(1)
'factorial' returned 1
Calling factorial(2)
'factorial' returned 2
Calling factorial(3)
'factorial' returned 6
Calling factorial(4)
'factorial' returned 24

Expected output:

Calling factorial(0)
'factorial' returned 1
Calling factorial(1)
'factorial' returned 1
Calling factorial(2)
'factorial' returned 2
Calling factorial(3)
'factorial' returned 6
Calling factorial(4)
'factorial' returned 24
2.708333333333333

Answer 1

It does return the value, but you don't print it after the call...

Do this:

print(approximate_e(5))