decorator.py

def trace(func):
    def print_in(*args, **kwargs):
        print('Executing function', func.__name__)
        return func(*args, **kwargs)
    return print_in
  
@trace
def calc(a,b):
    print(f'a+b is {a+b}, a-b is {a-b}.')  

calc(1,2)
# Executing function calc
# a+b is 3, a-b is -1.

@trace
def add_all(*args):
    print(reduce(lambda a,b:a+b, args))

a = add_all(1,2,3,4,5)
# Executing function add_all
# 15