class_docstr: Implements stacking of `num_frames` last frames of the game.
  
  Wraps an AtariPreprocessing object.
class_docstr_tok: ["Implements","stacking","of","`","num_frames","`","last","frames","of","the","game",".","Wraps","an","AtariPreprocessing","object","."]
code: def step(self, action: int):
      ob, reward, done, info = self.preproc.step(action)
      self.frames.append(ob)
      return self._get_array(), reward, done, info
  
file_path: flax/examples/ppo/env_utils.py
imports: import collections
  import gymnasium
  import numpy
  import seed_rl_atari_preprocessing
label_desc: Use image node_id 3 for calling the FrameStack obj's underlying member method code with example usage: obj.step(action) and returns: self,  reward,  done,  info