code: def swap(self, position: int) -> None:
          
          idx = -1 * position - 1
          try:
              self.values[-1], self.values[idx] = self.values[idx], self.values[-1]
          except IndexError:
              raise InsufficientStack("Insufficient stack items for SWAP{0}".format(position))
docs: Perform a SWAP operation on the stack.