""" Dessine avec turtle
    un damier         """
from turtle import *
def carrePlein(x,y,c):
    up()
    goto(x,y)
    down()
    begin_fill()
    for i in range(4):
        forward(c)
        left(90)
    end_fill()
    
def carreVide(x,y,c):
    up()
    goto(x,y)
    down()
    for i in range(4):
        forward(c)
        left(90)
    
c,n=30,4
#trace un damier de 2*n carrés de c de large sur chaque côté
ht()
speed(0)
x=-c*(n+1)
for i in range(2*n):
    x+=c
    y=-c*n
    for j in range(2*n):
        if (i+j)%2==0:
            carrePlein(x,y,c)
        y+=c
carreVide(-c*n,-c*n,2*c*n)