Append a :class:`ManageData <stellar_base.operation.ManageData>`
        operation to the list of operations.

        :param str data_name: String up to 64 bytes long. If this is a new Name
            it will add the given name/value pair to the account. If this Name
            is already present then the associated value will be modified.
        :param data_value: If not present then the existing
            Name will be deleted. If present then this value will be set in the
            DataEntry. Up to 64 bytes long.
        :type data_value: str, bytes, None
        :param str source: The source account on which data is being managed.
            operation.
        :return: This builder instance.

def append_manage_data_op(self, data_name, data_value, source=None):
        """Append a :class:`ManageData <stellar_base.operation.ManageData>`
        operation to the list of operations.

        :param str data_name: String up to 64 bytes long. If this is a new Name
            it will add the given name/value pair to the account. If this Name
            is already present then the associated value will be modified.
        :param data_value: If not present then the existing
            Name will be deleted. If present then this value will be set in the
            DataEntry. Up to 64 bytes long.
        :type data_value: str, bytes, None
        :param str source: The source account on which data is being managed.
            operation.
        :return: This builder instance.

        """
        op = operation.ManageData(data_name, data_value, source)
        return self.append_op(op)