Python Snake Game

import arcade
from random import randint

SCREEN_WIDTH = 600
SCREEN_HEIGHT = 600
CELL_WIDTH = 30


class Snake(arcade.Window):
    def __init__(self, width, height):
        super().__init__(width, height)
        arcade.set_background_color(arcade.color.BLACK)
        self.apple_pos = [SCREEN_WIDTH / 2, SCREEN_HEIGHT / 2 + CELL_WIDTH * 3]
        self.time = 0
        self.dir = 0  # 0, 1, 2, 3 = up, down, left, right, respectively
        self.snake = [[SCREEN_WIDTH / 2, SCREEN_HEIGHT / 2]]

    def on_update(self, delta_time):
        self.time += delta_time
        if self.time < .2:
            return

        next_pos = self.snake[0].copy()
        if self.dir == 0:
            next_pos[1] += CELL_WIDTH
        elif self.dir == 1:
            next_pos[1] -= CELL_WIDTH
        elif self.dir == 2:
            next_pos[0] -= CELL_WIDTH
        elif self.dir == 3:
            next_pos[0] += CELL_WIDTH

        if (next_pos in self.snake[1:] or
                not (0 <= next_pos[0] < SCREEN_WIDTH) or
                not (0 <= next_pos[1] < SCREEN_HEIGHT)):
            arcade.close_window()

        self.snake.insert(0, next_pos)
        if self.snake[0] == self.apple_pos:
            self.apple_pos = [randint(0, SCREEN_WIDTH // CELL_WIDTH - 1) * CELL_WIDTH,
                              randint(0, SCREEN_HEIGHT // CELL_WIDTH - 1) * CELL_WIDTH]
            while self.apple_pos in self.snake:
                self.apple_pos = [randint(0, SCREEN_WIDTH // CELL_WIDTH - 1) * CELL_WIDTH,
                                  randint(0, SCREEN_HEIGHT // CELL_WIDTH - 1) * CELL_WIDTH]
        else:
            self.snake.pop()

        self.time = 0

    def on_key_press(self, symbol, modifiers):
        if symbol in [arcade.key.UP, arcade.key.W]:
            self.dir = 0
        elif symbol in [arcade.key.DOWN, arcade.key.S]:
            self.dir = 1
        elif symbol in [arcade.key.LEFT, arcade.key.A]:
            self.dir = 2
        elif symbol in [arcade.key.RIGHT, arcade.key.D]:
            self.dir = 3

    def on_draw(self):
        self.clear()
        for i in self.snake:
            arcade.draw_rectangle_filled(
                i[0] + CELL_WIDTH // 2, i[1] + CELL_WIDTH // 2,
                CELL_WIDTH, CELL_WIDTH,
                arcade.color.GREEN
            )
        arcade.draw_rectangle_filled(
            self.apple_pos[0] + CELL_WIDTH // 2, self.apple_pos[1] + CELL_WIDTH // 2,
            CELL_WIDTH, CELL_WIDTH,
            arcade.color.RED
        )


Snake(SCREEN_WIDTH, SCREEN_HEIGHT)
arcade.run()