class_docstr: Base class for callback.
  
  :param verbose: (int)
class_docstr_tok: ["Base","class","for","callback",".",":","param","verbose",":","(","int",")"]
code: def _on_rollout_start(self) -> None:
      pass
  
imports: import os
  from abc import ABC
  import warnings
  import typing
  from typing import Union, List, Dict, Any, Optional
  import gym
  import numpy
  from stable_baselines.common.vec_env import VecEnv, sync_envs_normalization, DummyVecEnv
  from stable_baselines.common.evaluation import evaluate_policy
  from stable_baselines import logger
label_desc: Use image node_id 8 for calling the BaseCallback obj's underlying member method code with example usage: obj._on_rollout_start() without return types