from turtle import *

GRID_ROWS = 8

def draw_square(unit):
    for i in range(4):
        forward(unit)
        left(90)

def draw_grid(unit):
    "Draws a grid, with `unit` as the spacing."
    for cycle in range(2):
        for i in range(GRID_ROWS + 1):
            draw_square(i * unit)
        for side in range(2):
            forward(GRID_ROWS * unit)
            left(90)