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