Python向列表追加Point类变量时旧值被覆盖的问题排查

问题根源 #

Python中对象采用引用传递，你在循环外仅创建了一个curr_odom = Point()对象，每次循环只是修改该对象的属性值后追加到odom_record列表中。实际上列表里的所有元素都是指向同一个curr_odom对象的引用，当你更新新的里程计数据时，列表中之前所有元素的属性都会同步变化，导致odom_record[-1]和odom_record[-2]指向同一个对象、值完全相同，计算出的距离差始终为0。

修复代码 #

核心修改是每次循环创建新的Point对象，避免复用同一个对象引用：

def execute_callback(self, goal_handle):
        self.get_logger().info('Executing goal...')

        feedback_msg = OdomRecord.Feedback()
        feedback_msg.current_total = 0.0

        # 移除循环外的curr_odom定义，改为在循环内创建新对象
        # curr_odom = Point()

        self.odom_record = []
        self.last_x = 0.0
        self.last_y = 0.0
        self.second_last_x = 0.0
        self.second_last_y = 0.0
        self.total_distance = 0.0

        # 为初始值创建独立的Point对象，避免后续被意外修改
        self.first_odom = Point()
        self.first_odom.x = self.last_odom.x
        self.first_odom.y = self.last_odom.y

        self.odom_record.append(self.first_odom)

        iter = 0

        while True:
            iter += 1

            # 每次循环创建新的Point对象，存储当前里程计数据
            curr_odom = Point()
            curr_odom.x = self.last_odom.x
            curr_odom.y = self.last_odom.y
            curr_odom.z = self.last_odom.z

            self.odom_record.append(curr_odom)

            # 后续逻辑保持不变
            self.last_x = self.odom_record[-1].x
            self.last_y = self.odom_record[-1].y
            self.second_last_x = self.odom_record[-2].x
            self.second_last_y = self.odom_record[-2].y

            # DEBUGGING CODE...（省略原调试代码）

            self.total_distance = self.total_distance + self.dist_diff([self.last_x, self.last_y],
                                                                       [self.second_last_x, self.second_last_y])
            self.get_logger().warn(f"TOTAL DISTANCE= {self.total_distance}")

            feedback_msg.current_total = self.total_distance
            goal_handle.publish_feedback(feedback_msg)

            self.first_last_dist = self.dist_diff([self.last_odom.x, self.last_odom.y],
                                                  [self.first_odom.x, self.first_odom.y])

            self.get_logger().info(f"DISTANCE TO INITIAL POSITION= {self.first_last_dist}")

            if self.first_last_dist < 0.05 and iter > 5:
                self.get_logger().warn("INITIAL POSITION REACHED!")
                break

            time.sleep(1.0)

验证逻辑 #

修改后，每次追加到odom_record的都是独立的Point对象，各自保存当前时刻的里程计数据，后续修改新对象不会影响之前的元素。此时计算列表最后两个元素的距离差会得到真实的移动距离，total_distance将正常累加。

内容的提问来源于stack exchange，提问作者Elie