docstr: Called before preprocessing starts.
  
  :param config: The config dictionary.
docstr_tok: ["Called","before","preprocessing","starts",".",":","param","config",":","The","config","dictionary","."]
code: def on_preprocess_start(self, config: ModelConfigDict):
      """Called before preprocessing starts.
  
      :param config: The config dictionary.
      """
      pass
  
imports: from abc import ABC
  from typing import Any, Callable, Dict, List, Union
  from ludwig.api_annotations import PublicAPI
  from ludwig.types import HyperoptConfigDict, ModelConfigDict, TrainingSetMetadataDict
label_desc: Use image node_id 2 for calling the Callback obj's underlying member method code with example usage: obj.on_preprocess_start(config) without return types