input: def get_max_min(lst):
      """
      Get the maximum and minimum values in a given list.
      >>> get_max_min([1, 2, 3, 4, 5])
      (1, 5)
      >>> get_max_min([25, 13, 37, 19, 6])
      (6, 37)
      """
output:     if not lst:
          return None, None
      min_val = min(lst)
      max_val = max(lst)
      return min_val, max_val