Prepare SQL statement in HANA and cache it
        :param statement; a valid SQL statement
        :returns: statement_id (of prepared and cached statement)

def prepare(self, statement):
        """Prepare SQL statement in HANA and cache it
        :param statement; a valid SQL statement
        :returns: statement_id (of prepared and cached statement)
        """
        self._check_closed()
        self._column_types = None
        statement_id = params_metadata = result_metadata_part = None

        request = RequestMessage.new(
            self.connection,
            RequestSegment(
                message_types.PREPARE,
                Command(statement)
            )
        )
        response = self.connection.send_request(request)

        for part in response.segments[0].parts:
            if part.kind == part_kinds.STATEMENTID:
                statement_id = part.statement_id
            elif part.kind == part_kinds.PARAMETERMETADATA:
                params_metadata = part.values
            elif part.kind == part_kinds.RESULTSETMETADATA:
                result_metadata_part = part

        # Check that both variables have been set in previous loop, we need them:
        assert statement_id is not None
        assert params_metadata is not None
        # cache statement:
        self._prepared_statements[statement_id] = PreparedStatement(self.connection, statement_id,
                                                                    params_metadata, result_metadata_part)
        return statement_id