input: def get_max_min(lst):
      """Get the maximum and minimum values in a given list.
      >>> get_max_min([3, 5, 7, 2, 8])
      (2, 8)
      >>> get_max_min([10, 4, 1, 12, 6])
      (1, 12)
      """
output:     if not lst:
          return None
      max_val = lst[0]
      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)