code: def dataset(self, dataset_id, project=None):
          
          if project is None:
              project = self.project
  
          return DatasetReference(project, dataset_id)
docs: Construct a reference to a dataset.
  
          :type dataset_id: str
          :param dataset_id: ID of the dataset.
  
          :type project: str
          :param project: (Optional) project ID for the dataset (defaults to
                          the project of the client).
  
          :rtype: :class:`google.cloud.bigquery.dataset.DatasetReference`
          :returns: a new ``DatasetReference`` instance