code: def _stack(xs):
      try:
          return np.stack(xs)
      except ValueError:
          return np.stack(np.asarray(xs, dtype=object))
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import copy
  import multiprocessing.pool
  import time
  from absl import logging
  import gym
  import numpy
  from tensor2tensor.envs import env_problem
  from tensor2tensor.envs import trajectory
label_desc: Use image node_id 1 for calling a global function with example usage: _stack(xs) and returns: np, np