# Brownian motion -- an example of a multi-threaded Tkinter program.from Tkinter import *import randomimport threadingimport timeimport sysWIDTH = 400HEIGHT = 300SIGMA = 10BUZZ = 2RADIUS = 2LAMBDA = 10FILL = 'red'stop = 0                                # Set when main loop exitsdef particle(canvas):    r = RADIUS    x = random.gauss(WIDTH/2.0, SIGMA)    y = random.gauss(HEIGHT/2.0, SIGMA)    p = canvas.create_oval(x-r, y-r, x+r, y+r, fill=FILL)    while not stop:        dx = random.gauss(0, BUZZ)        dy = random.gauss(0, BUZZ)        dt = random.expovariate(LAMBDA)        try:            canvas.move(p, dx, dy)        except TclError:            break        time.sleep(dt)def main():    global stop    root = Tk()    canvas = Canvas(root, width=WIDTH, height=HEIGHT)    canvas.pack(fill='both', expand=1)    np = 30    if sys.argv[1:]:        np = int(sys.argv[1])    for i in range(np):        t = threading.Thread(target=particle, args=(canvas,))        t.start()    try:        root.mainloop()    finally:        stop = 1main()