class_docstr: Batch of environments inside the TensorFlow graph.
  
  The batch of environments will be stepped and reset inside of the graph using
  a tf.py_func(). The current batch of observations, actions, rewards, and done
  flags are held in according variables.
docstr: Number of combined environments.
docstr_tok: ["Number","of","combined","environments","."]
code: def __len__(self):
      """Number of combined environments."""
      return self.batch_size
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import copy
  import os
  import numpy
  from tensor2tensor.data_generators.gym_env import DummyWorldModelProblem
  from tensor2tensor.layers import common_layers
  from tensor2tensor.layers import common_video
  from tensor2tensor.rl.envs import in_graph_batch_env
  from tensor2tensor.utils import registry
  from tensor2tensor.utils import trainer_lib
  import tensorflow.compat.v1
  from tensorflow.compat.v1 import estimator
label_desc: Use image node_id 4 for calling the SimulatedBatchEnv obj's underlying member method code with example usage: obj.__len__() and returns: self