code: def data_format(self) -> Any:
      if self._config is None:
          raise RuntimeError("The config should be defined.")
      return self._config["data_format"]
  
imports: import json
  import os
  from typing import Any, Dict, List, Optional, Tuple
  from lightning.data.streaming.constants import _INDEX_FILENAME, _TORCH_GREATER_EQUAL_2_1_0
  from lightning.data.streaming.downloader import get_downloader_cls
  from lightning.data.streaming.item_loader import BaseItemLoader, PyTreeLoader, TokensLoader
  from lightning.data.streaming.sampler import ChunkedIndex
  from lightning.data.streaming.serializers import Serializer
label_desc: Use image node_id 5 for calling the ChunksConfig obj's underlying member method code with example usage: obj.data_format() and returns: self