code: def etag(cls, request, *args, **kwargs):
          '''Class method to generate an ETag for use with
          conditional processing; calls :meth:`datastream_etag` with
          class configuration.'''
          pid = kwargs[cls.pid_url_kwarg]
          date = kwargs.get(cls.as_of_date_url_kwarg, None)
          return datastream_etag(
              request, pid, cls.datastream_id,
              type=cls.object_type, repo=cls.repository_class(request=request),
              accept_range_request=cls.accept_range_request, as_of_date=datef etag(cls, request, *args, **kwargs):
          '''Class method to generate an ETag for use with
          conditional processing; calls :meth:`datastream_etag` with
          class configuration.'''
          pid = kwargs[cls.pid_url_kwarg]
          date = kwargs.get(cls.as_of_date_url_kwarg, None)
          return datastream_etag(
              request, pid, cls.datastream_id,
              type=cls.object_type, repo=cls.repository_class(request=request),
              accept_range_request=cls.accept_range_request, as_of_date=date)
docs: Class method to generate an ETag for use with
          conditional processing; calls :meth:`datastream_etag` with
          class configuration.