回溯（最近一次调用最后一次）：问题

Question

import pygame
import os
import random

pygame.font.init()

WIDTH = 750
HEIGHT = 600
WIN = pygame.display.set_mode((WIDTH, HEIGHT))
COOLDOWN = 30


#imageları yüklemek
# #arkaplan
BG = pygame.image.load(os.path.join('assets', 'background_space.png'))

#görev gemisi
MISSION_SHIP = pygame.image.load(os.path.join('assets', 'mission_ship.png'))

#düşman gemisi
RED_ENEMY_SHIP = pygame.image.load(os.path.join("assets", "enemy_ship_red.png"))
GREEN_ENEMY_SHIP = pygame.image.load(os.path.join("assets", "enemy_ship_green.png"))
BLUE_ENEMY_SHIP = pygame.image.load(os.path.join("assets", "enemy_ship_blue.png"))

#player lazerleri
PLAYER_LASER = pygame.image.load(os.path.join("assets", "blue_rocket.png"))

#düşman lazerleri
LASER01 = pygame.image.load(os.path.join("assets", "laser01.png"))
LASER02 = pygame.image.load(os.path.join("assets", "laser02.png"))
LASER03 = pygame.image.load(os.path.join("assets", "laser03.png"))

def collide(object1, object2):
    offset_x = object2.x - object1.x
    offset_y = object2.y - object1.y
    return object1.mask.overlap(object2.mask, (offset_x, offset_y)) != None

class Laser():
    def __init__(self, x, y, img):
        self.x = x
        self.y = y
        self.img = img
        self.mask = pygame.mask.from_surface(self.img)

    def move(self, velocity):
        self.y += velocity

    def draw(self, window):
        window.blit(self.img, (self.x, self.y))

    def collision(self, object):
        return collide(object, self)


class Ship():
    def __init__(self, x, y, health=100):

        self.x = x
        self.y = y
        self.health = health
        self.ship_img = None
        self.laser_img = None
        self.lasers = []
        self.cool_down_counter = 0

    def cool_down(self):
        if self.cool_down_counter >= COOLDOWN:
            self.cool_down_counter = 0
        else:
            self.cool_down_counter += 1
    def shoot(self):
        if self.cool_down_counter == 0:
            laser = Laser(self.x, self.y, self.laser_img)
            self.lasers.append(laser)

    def move_lasers(self, velocity, object):
        self.cool_down() #ne kadar sürede bir lazer atacak
        for laser in self.lasers:
            laser.move(velocity)
            if laser.collision(object):
                object.health -= 10 #düşman lazeri görev gemisine çarptığında canının 10'da 1'ini götür
                self.lasers.remove(laser) #lazer çarptıktan sonra lazeri yok et

    def draw(self, window):
        window.blit(self.ship_img, (self.x, self.y))
        for laser in self.lasers:
            laser.draw(window)

    def get_width(self):
        return self.ship_img.get_width()

    def get_height(self):
        return self.ship_img.get_height()


class PlayerShip(Ship):

    def __init__(self, x, y, health=100):
        super().__init__(x, y, health)
        self.ship_img = MISSION_SHIP
        self.lazer_img = PLAYER_LASER
        self.mask = pygame.mask.from_surface(self.ship_img)

    def shoot(self):
        if self.cool_down_counter == 0:
            laser = Laser(self.x+20, self.y, self.laser_img)
            self.lasers.append(laser)

    def move_lasers(self, velocity, objects):
        self.cool_down()
        for laser in self.lasers:
            laser.move(velocity)
            for object in objects:
                if laser.collision(object):
                    objects.remove(object) #düşman gemilerine lazer çarptığında germileri yok et
                    self.lasers.remove(laser)

class EnemyShip(Ship):
    COLOR_MAP = {
        "red": [RED_ENEMY_SHIP, LASER01],
        "green": [GREEN_ENEMY_SHIP, LASER02],
        "blue": [BLUE_ENEMY_SHIP, LASER03]
    }

    def __init__(self, x, y, color, health=100):
        super().__init__(x, y, health)
        self.ship_img, self.laser_img = self.COLOR_MAP[color]
        self.mask = pygame.mask.from_surface(self.ship_img)

    def move(self, velocity):
        self.y += velocity

    def shoot(self):
        if self.cool_down_counter == 0:
            laser = Laser(self.x+5, self.y, self.laser_img)
            self.lasers.append(laser)


def main():
    run = True
    FPS = 60  #saniye başına hareket hızı ayarlama
    enemies = []
    enemy_velocity = 1
    laser_velocity = 5
    enemy_length = 0
    level = 0

    main_font = pygame.font.SysFont("Algerian", 30)

    player_velocity = 5  #gemilerin hızı

    clock = pygame.time.Clock()

    player = PlayerShip(350, 490)

    def draws():
        WIN.blit(BG, (0, 0))
        player.draw(WIN)
        level_label = main_font.render("LEVEL: {}".format(level), 1, (255, 255, 255))
        WIN.blit(level_label, (600, 10))

        for enemy in enemies:
            enemy.draw(WIN)

        pygame.display.update()  #arkaplan resmini günceller

    while run:
        clock.tick(FPS)
        draws()

        if len(enemies) == 0:
            enemy_velocity += 1
            laser_velocity += 1
            enemy_length += 5
            level += 1
            global COOLDOWN
            COOLDOWN -= 5 #her seviyede 5 frame daha hızlı roket

            for i in range(enemy_length):
                enemy = EnemyShip(random.randrange(1, 700), random.randrange(-1500, -100),
                                  random.choice(["red", "blue", "green"]))

                enemies.append(enemy)

        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False  #programın sonsuz döngüye girmesini engeller

        keys = pygame.key.get_pressed()

        #gemiyi 4 yöne hareket ettirme
        if keys[pygame.K_LEFT] and player.x > 0:  #and kısmından sonrası geminin pencere dışına çıkmasını engeller
            player.x -= player_velocity

        if keys[pygame.K_RIGHT] and player.x < 670:
            player.x += player_velocity

        if keys[pygame.K_UP] and player.y > 0:
            player.y -= player_velocity

        if keys[pygame.K_DOWN] and player.y < 490:
            player.y += player_velocity

        if keys[pygame.K_SPACE]:
            player.shoot()


        for enemy in enemies:
            enemy.move(enemy_velocity)
            enemy.move_lasers(laser_velocity, player)
            if random.randrange(0, 10) == 1:
                enemy.shoot()

            if enemy.y > HEIGHT:
                enemies.remove(enemy)

        player.move_lasers(-laser_velocity, enemies)


main()

我认为我的代码没有问题，但是我运行游戏并按空格键射击，但游戏突然关闭并给出以下错误： 回溯（最近一次调用最后一次）： 文件“C:\用户