sierpinski carpet python turtle

1#!/usr/bin/env python3
2
3import turtle
4
5# --- functions ---
6
7def s(n, l):
8
9    if n == 0: # stop conditions
10
11        # draw filled rectangle
12
13        turtle.color('black')
14        turtle.begin_fill()
15        for _ in range (4):
16            turtle.forward(l)
17            turtle.left(90)
18        turtle.end_fill()
19
20    else: # recursion
21
22        # around center point create 8 smalles rectangles.
23        # create two rectangles on every side 
24        # so you have to repeat it four times
25
26        for _ in range(4):
27            # first rectangle
28            s(n-1, l/3)    
29            turtle.forward(l/3)
30
31            # second rectangle
32            s(n-1, l/3)    
33            turtle.forward(l/3)
34
35            # go to next corner
36            turtle.forward(l/3)
37            turtle.left(90)
38
39        # update screen
40        turtle.update()
41
42# --- main ---    
43
44# stop updating screen (to make it faster)
45turtle.tracer(0) 
46
47# start
48s(4, 400)
49
50# event loop
51turtle.done()
52