def step(self, action):
        """
        **Overview**:
            Execute one env step, process obs and return interaction result.
        """
        obs, reward, done, info = self.env.step(action)
        # Add optical flow channels into obs.
        state = self._process_obs(obs)
        # Update last frame.
        self.last_frame = obs
        return state, reward, done, info

        **Overview**:
            Execute one env step, process obs and return interaction result.
        
chapter3_obs/mario_wrapper.py