input: 
  def get_max_min(lst):
      """
      Given a list of numbers, return a tuple containing the minimum and maximum values.
  
      Examples:
      >>> get_max_min([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5])
      (1, 9)
      >>> get_max_min([-15, 0, 5, 10, -20, 25])
      (-20, 25)
      """
  
output:     if not lst:
          return None
      min_val = min(lst)
      max_val = max(lst)
      return (min_val, max_val)