input: def get_max_min(lst):
      """Return a tuple containing the minimum and maximum values in a given list.
      >>> get_max_min([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5])
      (1, 9)
      >>> get_max_min([-10, 0, 10, 20, -5])
      (-10, 20)
      >>> get_max_min([7])
      (7, 7)
      """
output:     if not lst:
          return 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)