A thread-less variant of brownian.py, submitted by Michele Simoniato.

Demo/tkinter/guido/brownian2.py

+# Brownian motion -- an example of a NON multi-threaded Tkinter program ;)
+# By Michele Simoniato, inspired by brownian.py
+
+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()