code: def observation(self, frame):
      
      if frame.shape == self.observation_space.shape:
        return frame
      else:
        extended_frame = np.zeros(self.observation_space.shape,
                                  self.observation_space.dtype)
        assert self.HW_AXES == (0, 1)
        extended_frame[:frame.shape[0], :frame.shape[1]] = frame
        return extended_frame
docs: Add single zero row/column to observation if needed.