code: def prepare_structure(self, input_dir: Optional[str]) -> Any:
      return self._inputs
  
imports: import inspect
  import os
  from datetime import datetime
  from pathlib import Path
  from types import FunctionType
  from typing import Any, Callable, Dict, Optional, Sequence, Union
  import torch
  from lightning.data.streaming.constants import _LIGHTNING_CLOUD_LATEST, _TORCH_GREATER_EQUAL_2_1_0
  from lightning.data.streaming.data_processor import DataChunkRecipe, DataProcessor, DataTransformRecipe
label_desc: Use image node_id 2 for calling the LambdaDataChunkRecipe obj's underlying member method code with example usage: obj.prepare_structure(input_dir) and returns: self