[Python-Dev] threadless brownian.py

Sun Apr 9 18:39:11 CEST 2006

Recently I downloaded Python 2.5a1 and I have started playing with it. In 
doing so,
I have been looking at the Demo directory in the distribution, to check if 
demos
of the new features have been added there. So, I rediscovered brownian.py,
in Demo/tkinter/guido. I just love this little program, because it reminds 
myself 
of one my first programs, a long long time ago (a brownian motion in 
AmigaBasic, 
with sprites!). It is also one of the first programs I looked at, when I 
started 
studying threads four years ago and I thought it was perfect. However, 
nowadays 
I know better and I have realized that brownian.py is perfect textbook example 
of a case where you don't really need threads, and you can use generators 
instead.
So I thought it would be nice to add a threadless version of brownian.py in
the Demo directory.
Here it is. If you like it, I donate the code to the PSF!
----------------------------
# Brownian motion -- an example of a NON multi-threaded Tkinter program ;)
from Tkinter import *
import random
import sys
WIDTH = 400
HEIGHT = 300
SIGMA = 10
BUZZ = 2
RADIUS = 2
LAMBDA = 10
FILL = 'red'
stop = 0 # Set when main loop exits
root = None # main window
def particle(canvas): # particle = iterator over the moves
 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)
 try:
 canvas.move(p, dx, dy)
 except TclError:
 break
 else:
 yield None
def move(particle): # move the particle at random time
 particle.next()
 dt = random.expovariate(LAMBDA)
 root.after(int(dt*1000), move, particle)
def main():
 global root, 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): # start the dance
 move(particle(canvas))
 try:
 root.mainloop()
 finally:
 stop = 1
if __name__ == '__main__':
 main()