input: def get_max_min(lst):
      """Finds the maximum and minimum values in the given list.
      >>> get_max_min([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5])
      (1, 9)
      >>> get_max_min([0, 0, 0, 0])
      (0, 0)
      >>> get_max_min([-2, -5, -7, -1, -10])
      (-10, -1)
      """
output:     if not lst:
          return None, None
      max_val = min_val = lst[0]
      for num in lst:
          if num > max_val:
              max_val = num
          if num < min_val:
              min_val = num
      return min_val, max_val