Pygame KEYUP，KEYDOWN导致幽灵移动

import pygame
from pygame.locals import *

# 初始化Pygame
pygame.init()

# 创建游戏窗口
screen = pygame.display.set_mode((800, 600))

# 定义幽灵的初始位置和速度
ghost_x = 400
ghost_y = 300
ghost_speed = 5

# 游戏主循环
running = True
while running:
    # 处理事件
    for event in pygame.event.get():
        if event.type == QUIT:
            running = False
        elif event.type == KEYDOWN:
            if event.key == K_LEFT:
                ghost_x -= ghost_speed
            elif event.key == K_RIGHT:
                ghost_x += ghost_speed
            elif event.key == K_UP:
                ghost_y -= ghost_speed
            elif event.key == K_DOWN:
                ghost_y += ghost_speed

    # 绘制游戏场景
    screen.fill((0, 0, 0))  # 清空屏幕
    pygame.draw.circle(screen, (255, 255, 255), (ghost_x, ghost_y), 20)  # 绘制幽灵

    # 更新屏幕
    pygame.display.flip()

# 退出游戏
pygame.quit()