code: def begin_transaction(self, project_id, transaction_options=None):
          
          request_pb = _datastore_pb2.BeginTransactionRequest()
          return _rpc(
              self.client._http,
              project_id,
              "beginTransaction",
              self.client._base_url,
              request_pb,
              _datastore_pb2.BeginTransactionResponse,
          )
docs: Perform a ``beginTransaction`` 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_options: ~.datastore_v1.types.TransactionOptions
          :param transaction_options: (Optional) Options for a new transaction.
  
          :rtype: :class:`.datastore_pb2.BeginTransactionResponse`
          :returns: The returned protobuf response object.