Python basic snake ai

import turtle, time, random

face = "stop"
body = []
gameover = False

wn = turtle.Screen()
wn.title("basic snake AI")
wn.setup(600, 600)
wn.tracer(0)

head = turtle.Turtle()
head.shape("square")
head.color("green")
head.goto(0,0)

apple = turtle.Turtle()
apple.shape("circle")
apple.color("red")
apple.penup()
apple.goto(0, 100)

def up():
    global face
    if face != "down":
        face = "up"

def down():
    global face
    if face != "up":
        face = "down"

def right():
    global face
    if face != "left":
        face = "right"

def left():
    global face
    if face != "right":
        face = "left"

wn.listen()
wn.onkeypress(up, "Up")
wn.onkeypress(down, "Down")
wn.onkeypress(left, "Left")
wn.onkeypress(right, "Right")

while True:
    wn.update()
    time.sleep(0)

    if head.xcor() > 290 or head.xcor() < -290 or head.ycor() > 290 or head.ycor() < -290:
        face = "stop"
        for i in body:
            i.goto(10000, 10000)
        body.clear()
        head.goto(0, 0)
        gameover = True

    if head.xcor() == apple.xcor() and head.ycor() == apple.ycor():
        x = random.randint(-14, 14)
        y = random.randint(-14, 14)
        apple.goto(x * 20, y * 20)

        new_segment = turtle.Turtle()
        new_segment.shape("square")
        new_segment.color("limegreen")
        new_segment.up()
        body.append(new_segment)

    ################ basic ai ################

    if head.ycor() == -280 and head.xcor() != -280: face = "left"
    if head.xcor() == -280 and head.ycor() != 280: face = "up"
    if head.ycor() == 280 and head.xcor() != 280: face = "right"
    if head.xcor() == 280 and head.ycor() != -280: face = "down"

    if head.xcor() ==  apple.xcor() and head.ycor() > apple.ycor(): face = "down"

    for segment in body:
        if face == "down" and head.ycor() - 20 == segment.ycor() and head.xcor() == segment.xcor(): face = "right"
        if face == "right" and head.xcor() + 20 == segment.xcor() and head.ycor() == segment.ycor(): face = "up"
        if face == "up" and head.ycor() + 20 == segment.ycor() and head.xcor() == segment.xcor(): face = "left"
        if face == "left" and head.xcor() - 20 == segment.xcor() and head.ycor() == segment.ycor(): face = "down"

    ############### end of ai ################

    if face == "up": head.sety(head.ycor() + 20)
    if face == "down": head.sety(head.ycor() - 20)
    if face == "left": head.setx(head.xcor() - 20)
    if face == "right": head.setx(head.xcor() + 20)

    for i in range(len(body)-1, 0, -1):
        body[i].goto(body[i-1].xcor(), body[i-1].ycor())

    if len(body) > 0:
        if face == "up":
            body[0].goto(head.xcor(), head.ycor() - 20)

        if face == "down":
            body[0].goto(head.xcor(), head.ycor() + 20)

        if face == "right":
            body[0].goto(head.xcor() - 20, head.ycor())

        if face == "left":
            body[0].goto(head.xcor() + 20, head.ycor())

    for segment in body:
        if segment.distance(head) == 0:
            face = "stop"
            for i in body:
                i.goto(10000, 10000)
            body.clear()
            gameover = True

    print(face)

    if gameover == True: break

wn.exitonclick()