在pygame中移动三角形

import pygame
import sys

pygame.init()
screen = pygame.display.set_mode((800, 600))

triangle_x = 400
triangle_y = 300
triangle_speed = 5

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        triangle_x -= triangle_speed
    if keys[pygame.K_RIGHT]:
        triangle_x += triangle_speed
    if keys[pygame.K_UP]:
        triangle_y -= triangle_speed
    if keys[pygame.K_DOWN]:
        triangle_y += triangle_speed

    screen.fill((255, 255, 255))
    pygame.draw.polygon(screen, (255, 0, 0), [(triangle_x, triangle_y), (triangle_x + 50, triangle_y + 50), (triangle_x - 50, triangle_y + 50)])
    pygame.display.flip()