Python Can anyone explain to me why when I try to run this code it just comes up with a black screen?

[Kroncker]

import pygame

import os

import time

import random

pygame.font.init()


WIDTH, HEIGHT = 750, 750

WIN = pygame.display.set_mode((WIDTH, HEIGHT))

pygame.display.set_caption("Space Shooter")


# Load Images

RED_SPACE_SHIP = pygame.image.load(os.path.join("assets", "pixel_ship_red_small.png"))

GREEN_SPACE_SHIP = pygame.image.load(os.path.join("assets", "pixel_ship_green_small.png"))

BLUE_SPACE_SHIP = pygame.image.load(os.path.join("assets", "pixel_ship_blue_small.png"))


# Player Ship

YELLOW_SPACE_SHIP = pygame.image.load(os.path.join("assets", "pixel_ship_yellow.png"))


# Lasers

RED_LASER = pygame.image.load(os.path.join("assets", "pixel_laser_red.png"))

GREEN_LASER = pygame.image.load(os.path.join("assets", "pixel_laser_green.png"))

BLUE_LASER = pygame.image.load(os.path.join("assets", "pixel_laser_blue.png"))

YELLOW_LASER = pygame.image.load(os.path.join("assets", "pixel_laser_yellow.png"))


#Background

BG = pygame.transform.scale(pygame.image.load(os.path.join("assets", "background-black.png")), (WIDTH, HEIGHT))


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 draw(self, window):

        window.blit(self.ship_img, (self.x, self.y))


    def get_width(self):

        return self.ship_img.get_width()


    def get_height(self):

        return self.ship_img.get_height()


class Player(Ship):

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

        super().__init__(x, y, health)

        self.ship_img = YELLOW_SPACE_SHIP

        self.laser_img = YELLOW_LASER

        self.mask = pygame.mask.from_surface(self.ship_img)

        self.max_health = health


class Enemy(Ship):

    COLOR_MAP = {

                "red": (RED_SPACE_SHIP, RED_LASER),

                "blue": (BLUE_SPACE_SHIP, BLUE_LASER),

                "green": (GREEN_SPACE_SHIP, GREEN_LASER)

                }


    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, vel):

        self.y += vel




def main():

    run = True

    FPS = 60

    level = 0

    lives = 5

    main_font = pygame.font.SysFont("comicsans", 50)


    enemies = []

    wave_length = 5

    enemy_vel = 1


    player_vel = 5


    player = Player(300, 650)


    clock = pygame.time.Clock()   


    def redraw_window():

        WIN.blit(BG, (0,0))

        # draw text

        lives_label = main_font.render(f"Lives: {lives}", 1, (255,255,255))

        level_label = main_font.render(f"Level: {level}", 1, (255,255,255))


        WIN.blit(lives_label, (10,10))

        WIN.blit(level_label, (WIDTH - level_label.get_width() - 10, 10))


        for enemy in enemies:

            enemy.draw(WIN)


        player.draw(WIN)



  

        pygame.display.update()


    while run:

        clock.tick(FPS)


        if len(enemies) == 0:

            level += 1

            wave_length += 5

            for i in range(wave_length):

                enemy = Enemy(random.randrange(50, WIDTH-100), random.randrange(-1500, -100), random.choice(["red", "blue", "green"]))

                enemies.append(enemy)


        for event in pygame.event.get():

            if event.type == pygame.QUIT:

                quit()


        keys = pygame.key.get_pressed()

        if keys[pygame.K_a] and player.x - player_vel > 0: # left

            player.x -= player_vel

        if keys[pygame.K_d] and player.x + player_vel + player.get_width() < WIDTH: # right

            player.x += player_vel

        if keys[pygame.K_w] and player.y - player_vel > 0: # up

            player.y -= player_vel

        if keys[pygame.K_s] and player.y + player_vel + player.get_height() < HEIGHT : # down

            player.y += player_vel


            for enemy in enemies:

                enemy.move(enemy_vel)


            redraw_window()

          

main()