import turtle

def draw_square():

        window = turtle.Screen()
        window.bgcolor("green")

        bob = turtle.Turtle()

        bob.forward(100)
        bob.right(90)
        bob.forward(100)
        bob.right(90)
        bob.forward(100)
        bob.right(90)
        bob.forward(100)
        bob.right(90)

        window.exitonclick()

draw_square()
