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 __init__(
      self,
      preproc: seed_rl_atari_preprocessing.AtariPreprocessing,
      num_frames: int,
  ):
      self.preproc = preproc
      self.num_frames = num_frames
      self.frames = collections.deque(maxlen=num_frames)
  
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 1 to create a new FrameStack object  with example: obj = FrameStack(preproc, num_frames)