def __init__(self, env=None):
        """Record episodes stats prior to EpisodicLifeEnv, etc."""
        gym.Wrapper.__init__(self, env)
        self._current_reward = None
        self._num_steps = None
        self._total_steps = None
        self._episode_rewards = []
        self._episode_lengths = []
        self._num_episodes = 0
        self._num_returned = 0