提问:
        老师,请问我这个为什么在代码运行正常的情况下按下键盘没有换方向呢?
import pygame
SCREEN_WIDTH = 700
SCREEN_HEIGHT = 500
BG_COLOR = pygame.Color(0, 0, 0)
TEXT_COLOR = pygame.Color(255, 0, 0)
class MainGame:  # 主类
    window = None
    my_tank = None
    def __init__(self):
        pass
    # 开始游戏
    def startGame(self):
        # 加载主窗口
        pygame.display.init()
        # 设置窗口大小及其显示
        MainGame.window = pygame.display.set_mode([SCREEN_WIDTH, SCREEN_HEIGHT])
        MainGame.my_tank = Tank(350, 250)
        # 设置标题
        pygame.display.set_caption('坦克大战1.03')
        while True:
            # 填充色
            MainGame.window.fill(BG_COLOR)
            # 获取事件
            self.getEvent()
            MainGame.window.blit(self.getTextSuface('敌方剩余坦克数量:%d' % 6), (10, 10))
            MainGame.my_tank.displayTank()
            pygame.display.update()
    # 结束游戏
    def endGame(self):
        print('谢谢使用')
        exit()
    # 左上角文字的绘制
    def getTextSuface(self, text):
        # 初始化字体模块
        pygame.font.init()
        # 获取字体font对象
        font = pygame.font.SysFont('kaiti', 18)
        # 绘制文字信息
        textSurface = font.render(text, True, TEXT_COLOR)
        return textSurface
    # 获取事件
    def getEvent(self):
        # 获取所有事件
        eventlist = pygame.event.get()
        for event in eventlist:
            # 判断
            if event.type == pygame.QUIT:
                self.endGame()
            if event.type == pygame.KEYDOWN:
                # 判断键盘按下
                if event.key == pygame.K_LEFT:
                    MainGame.my_tank.direction = 'L'
                    MainGame.my_tank.move()
                    print('按下左键')
                elif event.key == pygame.K_RIGHT:
                    MainGame.my_tank.direction = 'R'
                    MainGame.my_tank.move()
                    print('按下右键')
                elif event.key == pygame.K_UP:
                    MainGame.my_tank.direction = 'U'
                    MainGame.my_tank.move()
                    print('按下上键')
                elif event.key == pygame.K_DOWN:
                    MainGame.my_tank.direction = 'D'
                    MainGame.my_tank.move()
                    print('按下下键')
class Tank:  # 坦克类
    def __init__(self, left, top):
        self.images = {
            'U': pygame.image.load('img/p1tankU.gif'),
            'D': pygame.image.load('img/p1tankD.gif'),
            'L': pygame.image.load('img/p1tankL.gif'),
            'R': pygame.image.load('img/p1tankR.gif')
        }
        # 坦克默认朝向
        self.direction = 'R'
        self.image = self.images[self.direction]
        # 获取区域
        self.rect = self.image.get_rect()
        self.rect.left = left
        self.rect.top = top
        self.speed = 15
    # 展示
    def displayTank(self):
        MainGame.window.blit(self.image, self.rect)
    # 移动
    def move(self):
        if self.direction == 'L':
            self.rect.left -= self.speed
        elif self.direction == 'U':
            self.rect.top -= self.speed
        elif self.direction == 'D':
            self.rect.top += self.speed
        elif self.direction == 'R':
            self.rect.left += self.speed
    # 射击
    def shot(self):
        pass
class MyTank(Tank):  # 我方坦克类
    pass
class EnemyTank(Tank):  # 敌方坦克类
    # def __init__(self):
    pass
class Bullet:  # 子弹类
    def __init__(self):
        pass
    # 展示子弹
    def display(self):
        pass
    def move(self):
        pass
class Wall:  # 墙壁类
    def __init__(self):
        pass
    # 展示墙壁
    def display(self):
        pass
class Explode:  # 爆炸效果类
    def __init__(self):
        pass
    def displayExplode(self):
        pass
class Music:  # 音乐类
    def __init__(self):
        pass
    # 播放音乐
    def play(self):
        pass
if __name__ == '__main__':
    MainGame().startGame()