def __init__(self, user_id, **kwargs):
        super(BaseNotificationFeed, self).__init__(user_id, **kwargs)

        if self.markers_storage_class is None:
            if self.track_unread or self.track_unseen:
                raise ValueError('markers_storage_class must be set in case the unseen/unread activities are tracked')
        else:
            if not issubclass(self.markers_storage_class, BaseListsStorage):
                error_format = 'markers_storage_class attribute must be subclass of %s, encountered class %s'
                message = error_format % (BaseListsStorage, self.markers_storage_class)
                raise ValueError(message)

            markers_key = self.markers_key_format % {'user_id': user_id}
            self.feed_markers = self.markers_storage_class(key=markers_key,
                                                           max_length=self.markers_max_length)
dataset/ETHPy150Open tschellenbach/Stream-Framework/stream_framework/feeds/notification_feed/base.py/BaseNotificationFeed.__init__/original