class_docstr: Task for value training.
code: def trajectory_batch_stream(self):
      return self._trajectory_batch_stream
  
file_path: trax/trax/rl/value_tasks.py
imports: import copy
  import numpy
  from trax import layers
  from trax.fastmath import numpy
  from trax.supervised import training
label_desc: Use image node_id 2 for calling the ValueTrainTask obj's underlying member method code with example usage: obj.trajectory_batch_stream() and returns: self