为什么我在使用pygame的key.get_pressed功能时不能在屏幕上输入文本？

import pygame
from pygame.locals import *

pygame.init()

screen = pygame.display.set_mode((800, 600))
font = pygame.font.Font(None, 36)
text = ""

while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            exit()
        elif event.type == KEYDOWN:
            if event.key == K_BACKSPACE:
                text = text[:-1]
            elif event.key == K_RETURN:
                print("输入的文本为:", text)
                text = ""
            else:
                text += event.unicode

    screen.fill((255, 255, 255))
    rendered_text = font.render(text, True, (0, 0, 0))
    screen.blit(rendered_text, (10, 10))
    pygame.display.update()