class decorator_class(object):
    def __init__(self,original_function):
        self.original_function = original_function
    
    def __call__(self,*args,**kwargs):
        print("function name is {}".format(self.original_function.__name__))
        return self.original_function(*args,**kwargs)
    
@decorator_class
def sum(a, b):
    print("10 + 20 = ",a+b)
@decorator_class
def sub(a, b):
    print("20 - 10 = ",a-b)

sum(20, 10)
sub(20, 10)