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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 rollback(self, project_id, transaction):
 """Perform a ``rollback`` request. :type project_id: str :param project_id: The project to connect to. This is usually your project name in the cloud console. :type transaction: bytes :param transaction: The transaction ID to rollback. :rtype: :class:`.datastore_pb2.RollbackResponse` :returns: The returned protobuf response object. """

        request_pb = _datastore_pb2.RollbackRequest(
            project_id=project_id, transaction=transaction
        )
        # Response is empty (i.e. no fields) but we return it anyway.
        return _rpc(
            self.client._http,
            project_id,
            "rollback",
            self.client._base_url,
            request_pb,
            _datastore_pb2.RollbackResponse,
        )