如何在pygame中使用event.unicode删除字符串中添加的元素？

import pygame

pygame.init()

# 创建游戏窗口
screen = pygame.display.set_mode((500, 500))

# 创建字体对象
font = pygame.font.Font(None, 36)

# 初始化字符串
text = ""

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_BACKSPACE:
                if len(text) > 0:
                    text = text[:-1]

    screen.fill((255, 255, 255))
    
    # 渲染文本
    text_surface = font.render(text, True, (0, 0, 0))
    
    # 绘制文本
    screen.blit(text_surface, (50, 50))
    
    pygame.display.update()

pygame.quit()