Pygame乒乓游戏精灵无法移动且退出报video system not initialized错误

1. 精灵无法移动的问题 #

存在两处逻辑错误：

• 混淆了event.type和event.key属性：KEYDOWN/KEYUP属于事件类型，存放在event.type中，具体按下的按键值存放在event.key里，原代码判断按键时仍然调用event.type，自然匹配不到任何按键。
• 按键响应逻辑写反：应该是按键按下（KEYDOWN事件）时给移动速度赋值，按键松开（KEYUP事件）时将移动速度清零，原代码逻辑完全反转，无法触发移动。

2. 退出时报pygame.error: video system not initialized的问题 #

原代码在QUIT事件的处理逻辑里调用pygame.quit()后，没有立刻终止主循环，循环后续仍然会执行pygame.display.update()，此时pygame的视频系统已经被销毁，就会抛出该错误。需要把pygame.quit()放到主循环的外面，等所有逻辑执行完再调用。

修正后可正常运行的代码如下，额外增加了边界判断逻辑，避免球拍移出屏幕：

import pygame

# Initialization
pygame.init()
# Screen, Caption and Icon
width = 800
height = 600
screen = pygame.display.set_mode((width, height))
pygame.display.set_caption('PyGame')
icon = pygame.image.load('ping-pong.png')
pygame.display.set_icon(icon)
# Create Rects
player = pygame.Rect((5, 230), (10, 120))
opponent = pygame.Rect((785, 230), (10, 120))
# Game Variables
playerY_change = 0
opponentY_change = 0

game_over = False
while not game_over:
    # Coloring the Screen
    screen.fill((27, 35, 43))
    # Draw Rects
    pygame.draw.rect(screen, (255,255,255), player)
    pygame.draw.rect(screen, (255,255,255), opponent)
    # Managing Events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            game_over = True
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_UP:
                opponentY_change -= 3
            if event.key == pygame.K_DOWN:
                opponentY_change += 3
            if event.key == pygame.K_w:
                playerY_change -= 3
            if event.key == pygame.K_s:
                playerY_change += 3
        if event.type == pygame.KEYUP:
            if (event.key == pygame.K_UP) or (event.key == pygame.K_DOWN):
                opponentY_change = 0
            if (event.key == pygame.K_w) or (event.key == pygame.K_s):
                playerY_change = 0

    # 边界判断
    if player.top <= 0:
        player.top = 0
    if player.bottom >= height:
        player.bottom = height
    if opponent.top <= 0:
        opponent.top = 0
    if opponent.bottom >= height:
        opponent.bottom = height

    # Moving my sprites
    player.y += playerY_change
    opponent.y += opponentY_change
    # Updating the screen on every iter of loop
    pygame.display.update()

# 主循环结束后再退出pygame
pygame.quit()

内容的提问来源于stack exchange，提问作者Malik