input: def calculate_average(lst: List[float]) -> float:
      """Calculate the average of a list of numbers.
      >>> calculate_average([1, 2, 3, 4, 5])
      3.0
      >>> calculate_average([10, 20, 30, 40, 50])
      30.0
      """
output:     if not lst:
          return 0.0
      return sum(lst) / len(lst)