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, 5.0])
      3.0
      >>> avg_list([10, 20, 30])
      20.0
      """
output:     if not lst:
          return 0.0
      return sum(lst) / len(lst)