Python贪吃蛇

#基于pygame设计的贪吃蛇。
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import pygame,sys,random
SCREENx = 900
SCREENy = 900
class Snake():
#蛇类
    def __init__(self):
        self.dirction = pygame.K_RIGHT
        self.body = []
        for x in range(2):
            self.addnode()
    def addnode(self):
        left, top = (0, 0)
        if self.body:
            left, top = (self.body[0].left, self.body[0].top)
        node = pygame.Rect(left, top, 25, 25)
        if self.dirction == pygame.K_LEFT:
            node.left -= 25
        elif self.dirction == pygame.K_RIGHT:
            node.left += 25
        elif self.dirction == pygame.K_UP:
            node.top -= 25
        elif self.dirction == pygame.K_DOWN:
            node.top += 25
        self.body.insert(0, node)
    def delnode(self):
        self.body.pop()
    def isdead(self):
        if self.body[0].x not in range(SCREENx):
            return True
        if self.body[0].y not in range(SCREENy):
            return True
        if self.body[0] in self.body[1:]:
            return True
        return False
    def move(self):
        self.addnode()
        self.delnode()
    def changedirection(self, curkey):
        LR = [pygame.K_LEFT, pygame.K_RIGHT]
        UD = [pygame.K_UP, pygame.K_DOWN]
        if curkey in LR + UD:
            if (curkey in LR) and (self.dirction in LR):
                return
            if (curkey in UD) and (self.dirction in UD):
                return
            self.dirction = curkey
class Food:
#食物类
    def __init__(self):
        self.rect = pygame.Rect(-25, 0, 25, 25)
    def remove(self):
        self.rect.x = -25
    def set(self):
        if self.rect.x == -25:
            allpos = []
            for pos in range(25, SCREENx - 25, 25):
                allpos.append(pos)
            self.rect.left = random.choice(allpos)
            self.rect.top = random.choice(allpos)
#print(self.rect)
def show_text(screen, pos, text, color, font_bold=False, font_size=60, font_italic=False):
    cur_font = pygame.font.SysFont("宋体", font_size)
    cur_font.set_bold(font_bold)
    cur_font.set_italic(font_italic)
    text_fmt = cur_font.render(text, 1, color)
    screen.blit(text_fmt, pos)
def main(size=None):
    pygame.init()
    Ssize = (SCREENx, SCREENy)
    screen = pygame.display.set_mode(Ssize)
    pygame.display.set_caption('Snake')
    clock = pygame.time.Clock()
    scores = 0
    isdead = False
    snake = Snake()
    food = Food()
    while True:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
            if event.type == pygame.KEYDOWN:
                snake.changedirection(event.key)
                if event.key == pygame.K_SPACE and isdead:
                    return main()
        screen.fill((10, 10, 10))
        if not isdead:
            snake.move()
        for rect in snake.body:
            pygame.draw.rect(screen, (255, 255, 255), rect, 0)
        isdead = snake.isdead()
        if isdead:
            show_text(screen, (225, 400), 'press space to try again...', (225, 225, 225), False, 50)
        if food.rect == snake.body[0]:
            scores += 50
            food.remove()
            snake.addnode()
        food.set()
        pygame.draw.rect(screen, (255, 165, 50), food.rect, 0)
        show_text(screen, (50, SCREENy-100), str(scores), (225, 225, 225))
        pygame.display.update()
        clock.tick(15)
if __name__ == '__main__':
    main()