class_docstr: A convenient vocab container that can store multiple BaseVocab instances, and support 
  safe serialization of all instances via state dicts. Each subclass of this base class 
  should implement the load_state_dict() function to specify how a saved state dict 
  should be loaded back.
code: def __setitem__(self, key, item):
      self._vocabs[key] = item
  
imports: from copy import copy
  from collections import Counter, OrderedDict
  from collections.abc import Iterable
  import os
  import pickle
label_desc: Use image node_id 2 for calling the BaseMultiVocab obj's underlying member method code with example usage: obj.__setitem__(key, item) without return types