python tkinter实现屏保程序

#!/usr/bin/env python
 
from Tkinter import *
from random import randint
 
class RandomBall(object):
  def __init__(self, canvas, screenwidth, screenheight):
    self.canvas = canvas
    self.xpos = randint(10, int(screenwidth))
    self.ypos = randint(10, int(screenheight))
    self.xspeed = randint(6, 12)
    self.yspeed = randint(6, 12)
    self.screenwidth = screenwidth
    self.screenheight = screenheight
    self.radius = randint(40, 70)
    color = lambda : randint(0, 255)
    self.color = '#%02x%02x%02x' % (color(), color(), color())
 
  def create_ball(self):
    x1 = self.xpos - self.radius
    y1 = self.ypos - self.radius
    x2 = self.xpos + self.radius
    y2 = self.ypos + self.radius
    self.itm = self.canvas.create_oval(x1, y1, x2, y2, fill=self.color,
            outline=self.color)
 
  def move_ball(self):
    self.xpos += self.xspeed
    self.ypos += self.yspeed
    if self.ypos >= self.screenheight - self.radius:
      self.yspeed = -self.yspeed
    if self.ypos <= self.radius:
      self.yspeed = abs(self.yspeed)
    if self.xpos >= self.screenwidth - self.radius or self.xpos <= self.radius:
      self.xspeed = -self.xspeed
    self.canvas.move(self.itm, self.xspeed, self.yspeed)
 
class ScreenSaver:
  def __init__(self, num_balls):
    self.balls = []
    self.root = Tk()
    w, h = self.root.winfo_screenwidth(), self.root.winfo_screenheight()
    self.root.overrideredirect(1)
    self.root.attributes('-alpha', 0.3)
    self.root.bind('<Key>', self.myquit)
    self.root.bind('<Motion>', self.myquit)
    self.canvas = Canvas(self.root, width=w, height=h)
    self.canvas.pack()
    for i in range(num_balls):
      ball = RandomBall(self.canvas, screenwidth=w, screenheight=h)
      ball.create_ball()
      self.balls.append(ball)
    self.run_screen_saver()
    self.root.mainloop()
 
  def run_screen_saver(self):
    for ball in self.balls:
      ball.move_ball()
    self.canvas.after(50, self.run_screen_saver)
 
  def myquit(self, event):
    self.root.destroy()
 
if __name__ == "__main__":
  ScreenSaver(18)