我希望我在pygame中的角色不会离开屏幕。

import pygame
import sys

# 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")

# 定义角色
class Player(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 = (screen_width // 2, screen_height // 2)
        self.speed = 5

    def update(self):
        # 获取键盘输入
        keys = pygame.key.get_pressed()
        if keys[pygame.K_LEFT]:
            self.rect.x -= self.speed
        if keys[pygame.K_RIGHT]:
            self.rect.x += self.speed
        if keys[pygame.K_UP]:
            self.rect.y -= self.speed
        if keys[pygame.K_DOWN]:
            self.rect.y += self.speed

        # 边界检测
        if self.rect.left < 0:
            self.rect.left = 0
        if self.rect.right > screen_width:
            self.rect.right = screen_width
        if self.rect.top < 0:
            self.rect.top = 0
        if self.rect.bottom > screen_height:
            self.rect.bottom = screen_height

# 创建角色对象
player = Player()

# 创建精灵组
all_sprites = pygame.sprite.Group()
all_sprites.add(player)

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

    # 更新角色
    all_sprites.update()

    # 绘制背景
    screen.fill((255, 255, 255))

    # 绘制角色
    all_sprites.draw(screen)

    # 刷新屏幕
    pygame.display.flip()

# 退出游戏
pygame.quit()
sys.exit()