class_docstr: A general callback object that handles multiple events.
  
  This class has `on_backward`, `on_batch`, `on_epoch`, and `on_end` methods, corresponding to
  each callback type. Each one receives the state of the wrapper object as `self`.
  This enables easier state sharing between related callbacks.
  
  Also, this callback type is instantiated with `serialization_dir` and `on_start` is called
  with the trainer instance as an argument. This might be handy in case of callback logging
  and saving its own files next to the config/checkpoints/logs/etc.
code: def load_state_dict(self, state_dict: Dict[str, Any]) -> None:
      pass
  
file_path: allennlp/allennlp/training/callbacks/callback.py
imports: from typing import List, Dict, Any, Optional, TYPE_CHECKING
  import torch
  from allennlp.common import Registrable
  from allennlp.data import TensorDict
label_desc: Use image node_id 8 for calling the TrainerCallback obj's underlying member method code with example usage: obj.load_state_dict(state_dict) without return types