球被界线接住并粘在一起

Question

让我们考虑以下代码（中心和速度随机的球碰撞，屏幕表面边界相互碰撞）：import pygame,sys,mathfrom pygame.locals import *from random import randrangeWIDTH = 500HEIGHT = 500WHITE = (255,255,255)BLUE = (0, 0, 255)RADIUS = 10FPS = 30DISPLAYSURF = pygame.display.set_mode((WIDTH,HEIGHT),0,32)TAB = []fpsClock = pygame.time.Clock()pygame.display.set_caption('Animation')class Point:    def __init__(self, x, y):        self.x = x        self.y = y    def distance(self, A):        return math.sqrt((A.x-self.x)**2 + (A.y-self.y)**2)    def getTouple(self):        return (self.x,self.y)class Vector:    def __init__(self, x, y):        self.x = x        self.y = y    def norm(self):        return math.sqrt(self.x**2 + self.y**2)class Ball:    def __init__(self, center, radius, velocity):        self.center = center        self.radius = radius        self.velocity = velocity    def __init__(self):        self.radius = RADIUS        self.center = Point(randrange(RADIUS,WIDTH-RADIUS), randrange(RADIUS,HEIGHT-RADIUS))        vx = randrange(-5,5)        vy = randrange(-5,5)        while vx == 0 or vy == 0:            vx = randrange(-5,5)            vy = randrange(-5,5)        self.velocity = Vector(vx,vy)这段代码有效但不正确：有些球被边界“抓住”而其他球“粘在一起”。我认为问题出在Ball课堂方法上draw。对于如何改进该代码的任何想法，我将不胜感激。