What do you see? Draw this simple shape. Check out this Wikipedia article to know more about this illusion.
import turtle
screen = turtle.Screen()
screen.setup(500,500)
screen.title('Hermann Grid Illusion - PythonTurtle.Academy')
screen.tracer(0)
turtle.hideturtle()
turtle.speed(0)
turtle.bgcolor('black')
turtle.pensize(4)
turtle.color('light gray')
for x in range(-502,500,25):
turtle.up()
turtle.goto(x,-500)
turtle.down()
turtle.seth(90)
turtle.fd(1000)
for y in range(-502,500,25):
turtle.up()
turtle.goto(-500,y)
turtle.down()
turtle.seth(0)
turtle.fd(1000)
turtle.up()
for x in range(-502,500,25):
for y in range(-502,500,25):
turtle.goto(x,y)
turtle.dot('white')
screen.update()