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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def update_ddl(self, ddl_statements, operation_id=""):
 """Update DDL for this database. Apply any configured schema from :attr:`ddl_statements`. See https://cloud.google.com/spanner/reference/rpc/google.spanner.admin.database.v1#google.spanner.admin.database.v1.DatabaseAdmin.UpdateDatabase :type ddl_statements: Sequence[str] :param ddl_statements: a list of DDL statements to use on this database :type operation_id: str :param operation_id: (optional) a string ID for the long-running operation :rtype: :class:`google.api_core.operation.Operation` :returns: an operation instance :raises NotFound: if the database does not exist """

        client = self._instance._client
        api = client.database_admin_api
        metadata = _metadata_with_prefix(self.name)

        future = api.update_database_ddl(
            self.name, ddl_statements, operation_id=operation_id, metadata=metadata
        )
        return future