Perform a SWAP operation on the stack.

def swap(self, position: int) -> None:
        """
        Perform a SWAP operation on the stack.
        """
        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))