python中midbottom与blitme报错

以下代码显示:17行midbottom
19行blitme 拼错

import pygame


class Ship:

    # 管理飞船
    def __init__(self, ai_game):
        # 初始化
        self.screen = ai_game.screen
        self.screen_rect = ai_game.screen.get_rect()

        # 加载飞船图像
        self.image = pygame.image.load('images/Plane A.bmp')
        self.rect = self.image.get_rect()

        # 放在底部
        self.rect.midbottom = self.screen_rect.midbottom

    def blitme(self):
        self.screen.bilt(self.image, self.rect)

报错内容是啥，我这边定义的话，没报错