问当我添加sleep()部分时，我的tkinter窗口没有打开

EN

from tkinter import *
from time import sleep

window = Tk() 
cWidth = 800
cHeight = 500
c = Canvas(window, width = cWidth, height = cHeight, bg='black')
c.pack()
x = 400
y = 250
ball = c.create_polygon(x, y, x, y+25, x+25, y+25, x+25,y, fill='yellow')


Ball_move = 10

for i in range(200):
    c.move(ball, Ball_move, 0)
    window.update
    x += Ball_move
    if x == cWidth:
        Ball_move = -Ball_move
    sleep(0.5)

window.mainloop()