作业8

import turtle
turtle.speed(30)
turtle.penup()
off = True
for y in range(-40, 30 + 1, 10):
    for x in range(-40, 30 + 1, 10):
        if off:
            turtle.goto(x, y)
            turtle.pendown()
            turtle.begin_fill()
            turtle.color("black")
            turtle.forward(10)
            turtle.left(90)
            turtle.forward(10)
            turtle.left(90)
            turtle.forward(10)
            turtle.left(90)
            turtle.forward(10)
            turtle.left(90)
            turtle.end_fill()
            turtle.penup()
        else:
            turtle.goto(x, y)
            turtle.pendown()
            turtle.forward(10)
            turtle.left(90)
            turtle.forward(10)
            turtle.left(90)
            turtle.forward(10)
            turtle.left(90)
            turtle.forward(10)
            turtle.left(90)
            turtle.penup()
        off = bool(int(off) - 1)
    off = bool(int(off) - 1)
turtle.hideturtle()
turtle.done()