input: Write a function that takes two numbers as input, adds them together, and then doubles the result. If the input values are not provided, the function should return 0.
  
  def double_add(num1=0, num2=0): 
      return (num1 + num2) * 2
  
  assert double_add(3, 5) == 16
  assert double_add(10, 10) == 40
  assert double_add(-4, 4) == 0
  assert double_add() == 0
output: def double_add(num1=0, num2=0): 
      return (num1 + num2) * 2