input: 
  def avg_list(lst: List[float]) -> float:
      """Calculate the average of a list of numbers.
      
      >>> avg_list([1.0, 2.0, 3.0, 4.0])
      2.5
      >>> avg_list([10.5, 20.5, 30.0])
      20.333333333333332
      """
  
output:     if not lst:
          return 0.0
      return sum(lst) / len(lst)