Snake with Python Turtle Graphics

snake.py

from turtle import Turtle, bgcolor, setup, delay, onkey, listen, ontimer, title
import random

CELL_SIZE = 25
headTurtle = Turtle()
appleTurtle = Turtle()
textTurtle = Turtle()


setup(25 * 17 + 7, 25 * 17 + 7)
title("Snake!")
bgcolor(0, 1, 0)

headTurtle.shape("square")
headTurtle.color(0, 0, 1)
headTurtle.penup()
headTurtle.shapesize(25/20, 25/20)

appleTurtle.shape("circle")
appleTurtle.color(1, 0, 0)
appleTurtle.penup()
appleTurtle.shapesize(25/20, 25/20)

textTurtle.penup()
textTurtle.hideturtle()

delay(0)


def initialize():
    global gameStarted, heading, segments, stamps, initialSnakeLength, snakeLength, lastWent
    gameStarted = False
    segments = [(0, 0)]
    stamps = []
    initialSnakeLength = 3
    snakeLength = 3
    lastWent = None


initialize()


def spawnApple():
    global apple
    while True:
        apple = (random.randint(-8, 8), random.randint(-8, 8))
        if apple not in segments:
            drawApple()
            return


# We draw everything with an offset of 4 pixels up and the to left because the screen is off-center by default
def myGoto(turtle, x, y):
    turtle.goto(x-4, y+4)


def drawApple():
    appleTurtle.showturtle()
    myGoto(appleTurtle, apple[0] * CELL_SIZE, apple[1] * CELL_SIZE)


def clearApple():
    appleTurtle.hideturtle()


def upArrow():
    global heading
    if lastWent != "down":
        heading = "up"
    startGame()


def leftArrow():
    global heading
    if lastWent != "right":
        heading = "left"
    startGame()


def rightArrow():
    global heading
    if lastWent != "left":
        heading = "right"
    startGame()


def downArrow():
    global heading
    if lastWent != "up":
        heading = "down"
    startGame()


onkey(upArrow, "Up")
onkey(leftArrow, "Left")
onkey(rightArrow, "Right")
onkey(downArrow, "Down")
listen()


def moveHead(x, y):
    myGoto(headTurtle, x * CELL_SIZE, y * CELL_SIZE)


spawnApple()
moveHead(0, 0)


def startGame():
    global gameStarted
    if gameStarted:
        return
    gameStarted = True
    textTurtle.clear()  # Clear the game over text
    textTurtle.hideturtle()  # Hide the turtle again because clear() resets that
    drawApple()
    processTurn()


def processTurn():
    global snakeLength, gameStarted, lastWent
    currentHead = segments[-1]
    if heading == "up":
        newHead = (currentHead[0], currentHead[1] + 1)
    elif heading == "left":
        newHead = (currentHead[0] - 1, currentHead[1])
    elif heading == "right":
        newHead = (currentHead[0] + 1, currentHead[1])
    else:
        newHead = (currentHead[0], currentHead[1] - 1)
    lastWent = heading

    if newHead[0] < -8 or newHead[0] > 8 or newHead[1] < -8 or newHead[1] > 8:
        gameOver()
        return

    if newHead == apple:
        snakeLength += 1
        clearApple()

    # Delete the oldest segments to make sure the snake stays the right length
    while len(segments) > snakeLength - 1:
        segments.pop(0)

    if newHead in segments:
        gameOver()
        return

    segments.append(newHead)

    # stamp() creates a copy of the snake head so it stays there when it moves
    stamps.append(headTurtle.stamp())
    while len(stamps) > snakeLength - 1:
        headTurtle.clearstamp(stamps.pop(0))

    moveHead(newHead[0], newHead[1])
    if newHead == apple:
        spawnApple()

    # we can't use time.sleep because turtle can't process input while sleeping
    ontimer(processTurn, 200)


def gameOver():
    clearApple()
    points = snakeLength - initialSnakeLength
    textTurtle.goto(0, 40)
    textTurtle.color(.8, .6, .8)
    textTurtle.write(f"game over! points: {points}",
                     align="center", font=('Arial', 20, 'normal'))

    # Reset everything for the next game
    for stamp in stamps:
        headTurtle.clearstamp(stamp)
    initialize()
    moveHead(0, 0)