class_docstr: Trigger a callback every `n_steps` timesteps
  
  :param n_steps: (int) Number of timesteps between two trigger.
  :param callback: (BaseCallback) Callback that will be called
      when the event is triggered.
class_docstr_tok: ["Trigger","a","callback","every","`","n_steps","`","timesteps",":","param","n_steps",":","(","int",")","Number","of","timesteps","between","two","trigger",".",":","param","callback",":","(","BaseCallback",")","Callback","that","will","be","called","when","the","event","is","triggered","."]
code: def _on_step(self) -> bool:
      if (self.num_timesteps - self.last_time_trigger) >= self.n_steps:
          self.last_time_trigger = self.num_timesteps
          return self._on_event()
      return True
  
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 2 for calling the EveryNTimesteps obj's underlying member method code with example usage: obj._on_step() and returns: True, self