Szachownica

import turtle

okno = turtle.Screen()
stefan = turtle.Turtle()
stefan.speed(0)

bok = 50
x = 5
y = 4

stefan.penup()
stefan.goto(-x/2*bok,-y/2*bok)
stefan.pendown()

for k in range(y):
    for j in range(x):
        for i in range(4):
            stefan.forward(bok)
            stefan.left(90)
        stefan.forward(bok)
    stefan.backward(x*bok)
    stefan.left(90)
    stefan.forward(bok)
    stefan.right(90)

okno.mainloop()