input: 
  def double_add(num1, num2): 
      """ Generate a Python program that adds two then doubles the result.
      >>> double_add(2, 3)
      10
      >>> double_add(0, 0)
      0
      >>> double_add(-1, -1)
      -4
      """
      return (num1 + num2) * 2
  
output:     return (num1 + num2) * 2