code: def __len__(self) -> int:
      return len(self._storage)
  
imports: import random
  from typing import Optional, List, Union
  import numpy
  from stable_baselines.common.segment_tree import SumSegmentTree, MinSegmentTree
  from stable_baselines.common.vec_env import VecNormalize
label_desc: Use image node_id 2 for calling the ReplayBuffer obj's underlying member method code with example usage: obj.__len__() and returns: len