code: def init_from_datastore(self):
      
      self._data = {}
      for entity in self._datastore_client.query_fetch(
          kind=self._entity_kind_batches):
        batch_id = entity.key.flat_path[-1]
        self._data[batch_id] = dict(entity)
        self._data[batch_id]['images'] = {}
      for entity in self._datastore_client.query_fetch(
          kind=self._entity_kind_images):
        batch_id = entity.key.flat_path[-3]
        image_id = entity.key.flat_path[-1]
        self._data[batch_id]['images'][image_id] = dict(entity)
docs: Initializes batches by reading from the datastore.