Python Stoplights (Turtle Module / Classes)

# Python 3.6 Stoplight Class Demo using the Turtle Module
# by TokyoEdTech
# www.christianthompson.com

# Import the turtle module
# Set up the screen
import turtle
wn = turtle.Screen()
wn.title("Stoplights by @TokyoEdTech")
wn.bgcolor("black")

# Create the Stoplight class
class Stoplight():
    def __init__(self, x, y):
        self.red_light = turtle.Turtle()
        self.yellow_light = turtle.Turtle()
        self.green_light = turtle.Turtle()

        self.red_light.speed(0)
        self.yellow_light.speed(0)
        self.green_light.speed(0)

        self.red_light.color("grey")
        self.yellow_light.color("grey")
        self.green_light.color("grey")

        self.red_light.shape("circle")
        self.yellow_light.shape("circle")
        self.green_light.shape("circle")

        self.red_light.penup()
        self.yellow_light.penup()
        self.green_light.penup()

        self.red_light.goto(x, y + 40)
        self.yellow_light.goto(x, y)
        self.green_light.goto(x, y - 40)

        self.color = ""

        self.pen = turtle.Turtle()
        self.pen.penup()
        self.pen.width(3)
        self.pen.hideturtle()
        self.pen.speed(0)
        self.pen.color("yellow")
        self.pen.goto(x - 30, y + 60)
        self.pen.down()
        self.pen.fd(60)
        self.pen.rt(90)
        self.pen.fd(120)
        self.pen.rt(90)
        self.pen.fd(60)
        self.pen.rt(90)
        self.pen.fd(120)

    # Set the color of the stoplight
    def set_color(self, color):
        self.red_light.color("grey")
        self.yellow_light.color("grey")
        self.green_light.color("grey")

        if color == "red":
            self.red_light.color("red")
            self.color = "red"
        elif color == "yellow":
            self.yellow_light.color("yellow")
            self.color = "yellow"
        elif color == "green":
            self.green_light.color("green")
            self.color = "green"
        else:
            print("Error: Unknown Color")

    # Use a timer to change the stoplight
    def timer(self):
        if self.color == "red":
            self.set_color("green")
            wn.ontimer(self.timer, 2000)
        elif self.color == "yellow":
            self.set_color("red")
            wn.ontimer(self.timer, 2000)
        elif self.color == "green":
            self.set_color("yellow")
            wn.ontimer(self.timer, 1000)

# Create the first stoplight instance
stoplight = Stoplight(0, 0)
stoplight.set_color("red")
stoplight.timer()

# Create the second stoplight instance
stoplight2 = Stoplight(-100, 0)
stoplight2.set_color("yellow")
stoplight2.timer()

# Create the third stoplight instance
stoplight3 = Stoplight(100, 0)
stoplight3.set_color("green")
stoplight3.timer()

# Start the main events loop
wn.mainloop()