# Brownian motion -- an example of a multi-threaded Tkinter program.from tkinter import *import randomimport threadingimport timeimport sys#畫布大小WIDTH = 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)  #粒子數目  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()