python 外星人项目，外星人只能移动一行，其他行都不能移动，求解

Question

python 外星人项目，外星人只能移动一行，其他行都不能移动，求解？

主函数

import pygame 
from pygame.sprite import Group
from setting import Settings
from ship import Ship
import game_functions as gf
from alien import Alien

def run_game():
    pygame.init()    
    pygame.display.set_caption("Alien Invasion")
    game_settings = Settings()
    screen = pygame.display.set_mode((game_settings.screen_width,game_settings.screen_height))                
    game_ship = Ship(screen,game_settings)    #这里定game_alien = Alien(screen)义了game_ship，所以变量被函数gf.screen_update()调用的时候会能够使用bilt_ship()，#曾经我把这一句放到了while里面，ship移动后会重新回归中心，应该是调用了ship里面的__init__    ,
    bullets = Group()
    aliens = Group()
    gf.alien_number(game_settings,screen,game_ship,aliens)  #确定外星人行数和列树，并且存储到aliens里面
            
    while True:    
            
        gf.check_events(game_settings,game_ship,screen,bullets)
        game_ship.update_move()    
        gf.update_bullet(bullets)

        print("\n")
        for alien in aliens.sprites():        
            print((alien.rect.x,alien.rect.y) ,end='')

        gf.update_alien(aliens)    

        print("\n")
        for alien in aliens.sprites():        
            print((alien.rect.x,alien.rect.y) ,end='')
                
        gf.screen_update(screen,game_settings,game_ship,bullets,aliens)
        
run_game()

alien.py

import pygame
from pygame.sprite import Sprite 

class Alien(Sprite):
    def __init__(self,screen,game_settings):
        super(Alien,self).__init__()
        self.image = pygame.image.load("images/alien.png")
        self.screen = screen
        self.game_settings = game_settings
        self.rect = self.image.get_rect()
        '''
        self.rect.x = self.rect.width
        self.rect.y = self.rect.height
        '''
        self.x = float(self.rect.x)
        self.y = float(self.rect.y)
    def update(self):
        self.y += self.game_settings.alien_speed
        self.rect.y= self.y
        '''
        self.x += self.game_settings.alien_speed
        self.rect.x = self.x
        '''
    def blit_me(self):
        self.screen.blit(self.image,self.rect)

game_function.py

# coding=gbk
import sys    
import pygame
from bullet import Bullet
from alien import Alien

def check_events(game_settings,game_ship,screen,bullets):
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit()
        elif event.type == pygame.KEYDOWN:
            check_keydown_events(event,game_settings,game_ship,screen,bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,game_ship)

def check_keydown_events(event,game_settings,game_ship,screen,bullets):
        if event.key == pygame.K_RIGHT:
            game_ship.move_right = True
        elif event.key == pygame.K_LEFT:
            game_ship.move_left = True        
        elif event.key == pygame.K_SPACE:    
             fire_bullet(game_settings,game_ship,screen,bullets)

def fire_bullet(game_settings,game_ship,screen,bullets):
    if len(bullets) < game_settings.bullet_allow:
        new_bullet = Bullet(game_settings,game_ship,screen) 
        bullets.add(new_bullet)

def check_keyup_events(event,game_ship):
        if event.key == pygame.K_RIGHT:
            game_ship.move_right = False
        elif event.key == pygame.K_LEFT:
            game_ship.move_left = False

def screen_update(screen,game_settings,game_ship,bullets,aliens):
    screen.fill(game_settings.bg_color)
    for bullet in bullets.sprites():            
        bullet.draw_bullet()
    game_ship.bilt_ship()
    '''
    print("\n")
    for alien in aliens.sprites():        
        print((alien.rect.x,alien.rect.y) ,end='')
    '''    
    aliens.draw(screen)                
    pygame.display.flip()
    
def update_bullet(bullets):
    bullets.update()
    for bullet in bullets.copy():              
        if bullet.bullet_rect.bottom <= 0:
            bullets.remove(bullet)
        #print(len(bullets))        
    
def alien_number(game_settings,screen,game_ship,aliens):
    game_alien = Alien(screen, game_settings)
    alien_width =game_alien.rect.width
    screen_row_space = game_settings.screen_width - alien_width
    alien_row_No = int(screen_row_space/(2*alien_width))
    
    alien_height =game_alien.rect.height
    screen_col_space = game_settings.screen_height - 3*alien_height - game_ship.image_rect.height
    alien_col_No = int(screen_col_space/(3*alien_height))
    #print(alien_col_No)
    for sub_alien_col_No in range(alien_col_No):
        for sub_alien_row_No in range(alien_row_No):
            new_alien= Alien(screen,game_settings)
            new_alien.rect.x = sub_alien_row_No*2*alien_width + alien_width    
            new_alien.rect.y = sub_alien_col_No*2*alien_height +alien_height
            aliens.add(new_alien)
    
    '''
    print("\n")
    for alien in aliens.sprites():        
        print((alien.rect.x,alien.rect.y) ,end='')
    '''    
    
def update_alien(aliens):
    aliens.update()

setting.py

class Settings():
    def __init__(self):
        self.screen_width = 800
        self.screen_height = 650
        self.bg_color = (255,255,255)
        self.move_speed = 1
        
        self.bullet_speed = 10 #设置子弹速度
        self.alien_speed = 0.01
        self.bullet_color = 0,0,0 #设置子弹颜色
        self.bullet_width = 2 #子弹宽度    
        self.bullet_height = 5#子弹高度
        self.bullet_allow = 80#规定子弹总数量