Function Decorators With Parameters

In this example, we create a decorator that will multiply a value returned by a 2 parameters func by a value.

What we want to achieve

• Suppose you have a decorator and a function like the following:

1@mult(5)
2def add_nums(a,b):
3    return a+b

• The idea is that instead of having add_nums(3,4) return 7, it will return 35.
  It makes our function multiply the result by 5.
• Note, that for a decorator to work, it need not be called, it is just a reference to a decorator function that can enhance our target function.
• In other words:
  • mult is not a decorator
  • mult(5) return a decorator
  • this returned decorator will be called by @ operator to replace add_nums func.

A function to create a decorator

• Look at the following structure:

1def mult(num):
2    def mult_decorator(two_params_func):
3        def new_two_params_func(a,b):
4            temp = two_params_func(a,b)
5            return temp * num
6        return new_two_params_func
7    return mult_decorator

• The mult function IS NOT THE DECORATOR!
• Calling mult(5) returns the internal mult_decorator WHICH IS THE DECORATOR!
• The decorator is then called by python @ itself.
  It then returns the enhanced 2 parameter function.