Confusion: sensors in Ant example

In the ant.py. def _create_envs(). the env_senors are appends to the self.sensors right after a new sensor is appended to env_sensors.

         env_sensors = []
            for extr in extremity_names:
                extr_handle = self.gym.find_actor_rigid_body_handle(env_ptr, ant_handle, extr)
                env_sensors.append(self.gym.create_force_sensor(env_ptr, extr_handle, sensor_pose))
                self.sensors.append(env_sensors)

Should the last line be outside the for-loop? Or it is an intended design that I do not understand?