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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _depth_image_callback(self, image_msg):
 """ subscribe to depth image topic and keep it up to date """

        encoding = image_msg.encoding
        try:
            depth_arr = self._bridge.imgmsg_to_cv2(image_msg, encoding)
            import pdb; pdb.set_trace()

        except CvBridgeError as e:
            rospy.logerr(e)
        depth = np.array(depth_arr*MM_TO_METERS, np.float32)
        self._cur_depth_im = DepthImage(depth, self._frame)