Set the index (+1) where MIDDLE ends.

        :param int index: the new index for MIDDLE end

def middle_end(self, index):
        """
        Set the index (+1) where MIDDLE ends.

        :param int index: the new index for MIDDLE end
        """
        if (index < 0) or (index > self.all_length):
            raise ValueError(u"The given index is not valid")
        self.__middle_end = index