python - Tkinter canvas animation flicker -

i wrote python program tkinter makes ball bounce around screen. works great, except 1 problem: outermost edges of ball flicker ball moves.

i understand tkinter automatically double buffering, thought shouldn't having problems tearing. i'm not sure error coming from. ideas on how can rid of it?

code below. here's gist of it: class ball extends tk , gets created when program run. sets game, encapsulating in gmodel. gmodel runs game run() , loops on , over, calling update().

import threading time import sleep, clock tkinter import * tkinter import ttk  speed = 150  # pixels per second width = 400 height = 500 rad = 25 pause = 0  # time added between frames.  slows things down if necessary  class gmodel:     # contains game data.      def __init__(self, can):         # can canvas draw on         self.can = can         self.circ = can.create_oval(0,0, 2*rad, 2*rad)          # position , velocity of ball         self.x, self.y = rad, rad         self.dx, self.dy = speed, speed          # ball moving?         self.is_running = true      def update(self, elapsed_time):         # updates dynamic game variables.  elapsed_time in seconds.         change_x = self.dx * elapsed_time         change_y = self.dy * elapsed_time          self.can.move(self.circ, change_x, change_y)         self.x += change_x         self.y += change_y          self.resolve_collisions()      def resolve_collisions(self):         # if ball goes off edge, put , reverse velocity         if self.x - rad < 0:             self.x = rad             self.dx = speed         elif self.x + rad > width:             self.x = width - rad             self.dx = -speed          if self.y - rad < 0:             self.y = rad             self.dy = speed         elif self.y + rad > height:             self.y = height - rad             self.dy = -speed      def end_game(self):         self.is_running = false      def run(self):         last_time = 0.0          while self.is_running:             # number of seconds since last iteration of loop             this_time = clock()             elapsed_time = this_time - last_time             last_time = this_time              try:   # use here in case window gets x'd while t still runs                 self.update(elapsed_time)             except:                 self.is_running = false              if (pause > 0):                 sleep(pause)  # slow things down if necessary  class ball(tk):     def __init__(self):         tk.__init__(self)          self.can = canvas(self, width=width, height=height)         self.can.grid(row=0, column=0, sticky=(n, w, e, s))         self.gm = gmodel(self.can)      def mainloop(self):         t = threading.thread(target=self.gm.run, daemon=true)         t.start()         tk.mainloop(self)  def main():     ball().mainloop()  if __name__ == "__main__":     main()