code: def __getitem__(self, key):
      try:
          return collections.UserDict.__getitem__(self, key)
      except KeyError:
          collections.UserDict.__setitem__(
              self, key, copy.deepcopy(self.model)
          )
          return self[key]
  
imports: from __future__ import annotations
  import collections
  import copy
  import functools
  import random
  from river import base, linear_model
  from river.utils.math import minkowski_distance, prod
label_desc: Use image node_id 3 for calling the BaseChain obj's underlying member method code with example usage: obj.__getitem__(key) and returns: collections, self