Python Paddle oluşuyor ancak hareket etmiyor

#main.py

import time
from turtle import Screen
from paddle import Paddle

screen = Screen()
screen.bgcolor("black")
screen.setup(width=800, height=600)
screen.title("Pong")
screen.listen()
screen.tracer(0)

paddle = Paddle()

screen.onkey(paddle.up, "Up")
screen.onkey(paddle.down, "Down")

game_is_on = True
while game_is_on:
    screen.update()
    time.sleep(0.1)

screen.exitonclick()

#paddle.py

from turtle import Turtle

STARTING_POSITION = (350, 0)


class Paddle(Turtle):
    def __init__(self):
        super().__init__()
        self.paddle_position = []
        self.create_paddle()

    def create_paddle(self):
        paddle = Turtle("square")
        paddle.color("white")
        paddle.shapesize(stretch_wid=5, stretch_len=1)
        paddle.penup()
        paddle.goto(STARTING_POSITION)
        self.paddle_position.append((paddle.xcor(), paddle.ycor()))

    def up(self):
        new_paddle_position = (self.paddle_position[0][0], self.paddle_position[0][1] + 20)
        self.goto(new_paddle_position)
        self.paddle_position[0] = new_paddle_position
        print(self.paddle_position)

    def down(self):
        new_paddle_position = (self.paddle_position[0][0], self.paddle_position[0][1] - 20)
        self.goto(new_paddle_position)
        self.paddle_position[0] = new_paddle_position
        print(self.paddle_position)