code: def __len__(self):
      return len(self._storage)
  
imports: import argparse
  import operator
  import os
  import random
  import time
  import gym
  import matplotlib.pyplot
  import numpy
  import tensorflow
  import tensorlayer
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