我正在用pygame做一个游戏，我想让它多次产生一个东西。

import pygame
import random

# 初始化Pygame
pygame.init()

# 设置屏幕尺寸
screen_width = 800
screen_height = 600
screen = pygame.display.set_mode((screen_width, screen_height))
pygame.display.set_caption("My Game")

# 定义物体类
class Object(pygame.sprite.Sprite):
    def __init__(self):
        super().__init__()
        self.image = pygame.Surface((50, 50))
        self.image.fill((255, 0, 0))
        self.rect = self.image.get_rect()
        self.rect.center = (random.randint(0, screen_width), random.randint(0, screen_height)))

    def update(self):
        self.rect.y += 1
        if self.rect.y > screen_height:
            self.rect.y = 0

# 创建物体组
objects = pygame.sprite.Group()

# 生成多个物体实例
num_objects = 10
for _ in range(num_objects):
    obj = Object()
    objects.add(obj)

# 游戏主循环
running = True
while running:
    # 事件处理
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # 更新物体位置
    objects.update()

    # 渲染屏幕
    screen.fill((0, 0, 0))
    objects.draw(screen)
    pygame.display.flip()

# 退出游戏
pygame.quit()