input: def get_max_min(lst):
      """
      Get the maximum and minimum values in a given list of numbers.
      
      >>> get_max_min([3, 5, 1, 2, 4])
      (1, 5)
      >>> get_max_min([10])
      (10, 10)
      >>> get_max_min([-1, -5, -3, -2, -4])
      (-5, -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
          elif num < min_val:
              min_val = num
      return min_val, max_val