How to use the stable-baselines.stable_baselines.common.vec_env.base_vec_env.VecEnv function in stable-baselines

def _get_indices(self, indices):
        """
        Convert a flexibly-typed reference to environment indices to an implied list of indices.

        :param indices: (None,int,Iterable) refers to indices of envs.
        :return: (list) the implied list of indices.
        """
        if indices is None:
            indices = range(self.num_envs)
        elif isinstance(indices, int):
            indices = [indices]
        return indices


class VecEnvWrapper(VecEnv):
    """
    Vectorized environment base class

    :param venv: (VecEnv) the vectorized environment to wrap
    :param observation_space: (Gym Space) the observation space (can be None to load from venv)
    :param action_space: (Gym Space) the action space (can be None to load from venv)
    """

    def __init__(self, venv, observation_space=None, action_space=None):
        self.venv = venv
        VecEnv.__init__(self, num_envs=venv.num_envs, observation_space=observation_space or venv.observation_space,
                        action_space=action_space or venv.action_space)
        self.class_attributes = dict(inspect.getmembers(self.__class__))

    def step_async(self, actions):
        self.venv.step_async(actions)