我想使球从边界墙弹起。目前，我的圈子应该撞墙，然后改变速度并朝相反的方向移动，但这并没有发生。我将不胜感激:)谢谢

from graphics import*
from random import*
from time import*

win = GraphWin('My Program', 600, 600)
win.setBackground('pink')
my_circle = Circle(Point(200,300),30)
my_circle.setFill('blue')
my_circle.setOutline('darkorchid1')
my_circle.draw(win)

key = win.checkKey()
while key == '':  
    
    vel_x = randint(-30,30)
    vel_y = randint(-30,30)
    my_circle.move(vel_x, vel_y)
    sleep(0.1)
    
    
    for bounce in range(600):
    
        find_center = my_circle.getCenter()
        center_x = find_center.getX()
        center_y = find_center.getY()
        
        if center_x == 600 or center_y == 600:
            vel_x = -randint(30,-30)
            vel_y = -randint(30,-30)
            my_circle.move(vel_x, vel_y)
            sleep(0.1)
    key = win.checkKey()