input: 
  def double_add(num1, num2): 
      """Given two numbers, add them together and then double the result.
      >>> double_add(1, 2)
      6
      >>> double_add(0, 0)
      0
      >>> double_add(-1, 1)
      0
      """
      return (num1 + num2) * 2
  
output:     return (num1 + num2) * 2