《外星人入侵》之计分功能

计分和游戏控制

我们在玩游戏时，都有计分的制度，随着分数的增长，玩家玩游戏的精神也在增长，哈哈。
并且游戏都有一个控制按钮，比如开始，或者结束。

1.添加Play按钮

我们先让游戏一开始处于非活动状态，并提示玩家单击Play按钮来开始游戏。为此，在game_stats.py中添加代码：
game_stats.py

class GameStats():
    """跟踪游戏的统计信息"""

    def __init__(self,ai_settings):
        """初始化统计信息"""
        self.ai_settings = ai_settings
        self.reset_stats()

        #游戏刚开始处于非活动状态
        self.game_active = False

    def reset_stats(self):
        """初始化在游戏运行期间可能变化的统计信息"""
        self.ships_left = self.ai_settings.ship_limit

1.1 创建Button类

由于Pygame没有内置创建按钮的方法，我们创建一个Button类，用于创建带标签的实心矩形，可以使用这些代码来创建任何按钮。我们保存文件名为button.py

import pygame.font #导入模块pygame.font，它让Pygame能够将文本渲染到屏幕上

class Button():

    def __init__(self,ai_settings,screen,msg):
        """初始化按钮的属性"""
        self.screen = screen
        self.screen_rect = screen.get_rect()

        #设置按钮的尺寸和其他属性
        self.width,self.height = 200, 50
        self.button_color = (0,255,0)
        self.text_color = (255,255,255)
        self.font = pygame.font.SysFont(None,48)
        #我们使用字体来渲染渲染文本，实参None让Pygame使用默认字体，而48指定了文本的字号

        #创建按钮的rect对象，并使其居中
        self.rect = pygame.Rect(0,0,self.width,self.height)
        self.rect.center = self.screen_rect.center

        #按钮的标签只需创建一次
        self.prep_msg(msg)
        #Pygame通过将你要显示的字符串渲染为图像来处理文本

然后完成prep_msg的代码：
button.py

import pygame.font

class Button():

    def __init__(self,ai_settings,screen,msg):
        """初始化按钮的属性"""
        self.screen = screen
        self.screen_rect = screen.get_rect()

        #设置按钮的尺寸和其他属性
        self.width,self.height = 200, 50
        self.button_color = (0,255,0)
        self.text_color = (255,255,255)
        self.font = pygame.font.SysFont(None,48)

        #创建按钮的rect对象，并使其居中
        self.rect = pygame.Rect(0,0,self.width,self.height)
        self.rect.center = self.screen_rect.center

        #按钮的标签只需创建一次
        self.prep_msg(msg)

    def prep_msg(self,msg):
        """将msg渲染为图像，并使其在按钮上居中"""
        #msg 要渲染为图像的文本
        #font.render()将存储在msg中的文本转换为图像，然后存储在msg_image中，第二个实参指定是否开启反锯齿功能
        #反锯齿功能：让文本的边缘更平滑
        self.msg_image = self.font.render(msg,True,self.text_color,self.button_color)
        self.msg_image_rect = self.msg_image.get_rect()
        self.msg_image_rect.center = self.rect.center

最后我们创建方法draw_button()，通过调用它来将按钮显示到屏幕上：
button.py

import pygame.font

class Button():

    def __init__(self,ai_settings,screen,msg):
        """初始化按钮的属性"""
        self.screen = screen
        self.screen_rect = screen.get_rect()

        #设置按钮的尺寸和其他属性
        self.width,self.height = 200, 50
        self.button_color = (0,255,0)
        self.text_color = (255,255,255)
        self.font = pygame.font.SysFont(None,48)

        #创建按钮的rect对象，并使其居中
        self.rect = pygame.Rect(0,0,self.width,self.height)
        self.rect.center = self.screen_rect.center

        #按钮的标签只需创建一次
        self.prep_msg(msg)

    def prep_msg(self,msg):
        """将msg渲染为图像，并使其在按钮上居中"""
        #msg 要渲染为图像的文本
        #font.render()将存储在msg中的文本转换为图像，然后存储在msg_image中，第二个实参指定是否开启反锯齿功能
        #反锯齿功能：让文本的边缘更平滑
        self.msg_image = self.font.render(msg,True,self.text_color,self.button_color)
        self.msg_image_rect = self.msg_image.get_rect()
        self.msg_image_rect.center = self.rect.center

    def draw_button(self):
        #绘制一个用颜色填充的按钮，在绘制文本
        self.screen.fill(self.button_color,self.rect)  #h绘制按钮的矩形
        self.screen.blit(self.msg_image,self.msg_image_rect) #传递一幅图像与该图像关联的rect对象

1.2 在屏幕上绘制按钮

接下来我们就是用button类来创建一个play按钮，在alien_invasion.py中直接创建

import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例
    stats = GameStats(ai_settings)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

        sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,ship,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button)


run_game()

接下来需要修改update_screen方法。
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, ship, bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
           
                
def update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        bullets.empty()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

1.3 开始游戏

现在屏幕上面已经有了，play按钮，但当点击play按钮开始游戏，还需添加一些代码，以监视与这个按钮相关的鼠标事件：
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(stats,play_button,mouse_x,mouse_y)

def check_play_button(stats,play_button,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    if play_button.rect.collidepoint(mouse_x,mouse_y):
        stats.game_active = True
           
                
def update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        bullets.empty()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

alien_invasion.py

import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例
    stats = GameStats(ai_settings)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

     #   sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,stats,play_button,ship,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button)


run_game()

1.4 重置游戏

前面编写的代码只处理了玩家第一次单击Play按钮的情况，而没有处理游戏结束的情况，因为没有重置导致游戏结束的条件。
为在玩家每次单击Play按钮时都重置游戏，需要重置统计信息，删除现有的外星人和子弹，创建一群新的外星人，并让飞船居中。
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    if play_button.rect.collidepoint(mouse_x,mouse_y):
        #重置游戏统计信息
        stats.reset_status()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        bullets.empty()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

alien_invasion.py

import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例
    stats = GameStats(ai_settings)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

     #   sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,stats,play_button,ship,aliens,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button)


run_game()

1.5 将Play按钮切换到非活动状态

当前的play按钮存在一个问题，那就是即便Play按钮不可见，玩家单击其原来所在区域时，游戏依然会做出响应。游戏开始后，如果玩家不小心单击了Play按钮原来所处的区域，游戏将重新开始。
那怎么修改这个bug呢？我们让游戏在game_active为False时才开始：
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
     button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        bullets.empty()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

2. 提高等级

下面为游戏添加点有趣的玩法：每当玩家将屏幕上的外星人都消灭干净后，加快游戏的节奏，让游戏玩起来更难。

2.1 修改速度设置

我们首先需要重新组织settings类，将游戏设置划分成静态的和动态的两组。对于随着游戏进行而变化的设置，我们还确保它们在开始新游戏时被重置。
settings.py

class Settings():
    """存储<<外星人入侵>>的所有设置的类"""

    def __init__(self):
        """初始化游戏的设置"""
        #屏幕设置
        self.screen_width = 800
        self.screen_height = 600
        self.bg_color = (230,230,230)

        #飞船的设置
        self.ship_speed_factor = 1.5
        self.ship_limit = 3

        #子弹设置
        self.bullet_speed_factor = 3
        self.bullet_width = 3
        self.bullet_height = 15
        self.bullet_color = (60 , 60 , 60)
        self.bullets_allowed = 5   #将在屏幕内可以存在的子弹限制为3颗

        #外星人设置
        self.alien_speed_factor = 1
        self.fleet_drop_speed = 10

        #以什么样的速度加快游戏节奏
        self.speedup_scale = 1.1
        self.initialize_dynamic_settings()
        

    
    def initialize_dynamic_settings(self):
        """初始化随游戏进行而变化的设置"""

        #该方法设置了飞船、子弹和外星人的初始速度
        self.ship_speed_factor = 1.5
        self.bullet_speed_factor = 3
        self.alien_speed_factor = 1

        #fleet_direction为1表示向右移，为-1表示向左移
        self.fleet_direction = 1

    def increase_speed(self):
        """提高速度设置"""

        #使用该方法在玩家提高一个等级时，来提高飞船、子弹和外星人的速度
        self.ship_speed_factor *= self.speedup_scale
        self.bullet_speed_factor *= self.speedup_scale
        self.alien_speed_factor *=self.speedup_scale

game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

2.2 重置速度

每当玩家开始新游戏时，都需要将发生了变化的设置重置为初始值，否则新游戏开始时，速度设置将是前一次游戏增加了的值：
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()
        
        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

然后我们运行程序后，就会发现，随着消灭的外星人越多，游戏的节奏越来越快，也越来越紧张…

3 记分

下面为游戏添加一个计分系统，来实时地跟踪玩家的得分，并显示最高得分、当前等级和余下的飞船数。
得分是游戏的一项统计信息，因此我们在GameStats中添加一个score属性：
game_stats.py

class GameStats():
    """跟踪游戏的统计信息"""

    def __init__(self,ai_settings):
        """初始化统计信息"""
        self.ai_settings = ai_settings
        self.reset_stats()

        #游戏刚开始处于非活动状态
        self.game_active = False

    def reset_stats(self):
        """初始化在游戏运行期间可能变化的统计信息"""
        self.ships_left = self.ai_settings.ship_limit
        self.score = 0

3.1 显示得分

为了在屏幕上显示得分，我们创建一个新类Scoreboard，保存在scoreboard.py中：
scoreboard.py

import pygame.font

class Scoreboard():
    """显示得分信息的类"""

    def __init__(self,ai_settings,screen,stats):
        """初始化显示得分涉及的属性"""

        self.screen  = screen
        self.screen_rect = screen.get_rect()
        self.ai_settings = ai_settings
        self.stats = stats

        #显示得分信息时使用的字体设置
        self.text_color = (30,30,30)
        self.font = pygame.font.SysFont(None,48)

        #准备初始得分图像
        self.prep_score()

    def prep_score(self):
        """将得分转换为一副渲染的图像"""
        score_str = str(self.stats.score)
        self.score_image = self.font.render(score_str,True,self.text_color,self.ai_settings.bg_color)

        #将得分放在屏幕右上角
        self.score_rect = self.score_image.get_rect()
        self.score_rect.right = self.screen_rect.right - 20
        self.score_rect.top = 20

    def show_score(self):
        """在屏幕上显示得分"""
		#这个方法把得分图像显示在屏幕上
        self.screen.blit(self.score_image,self.score_rect)

3.2 创建记分牌

为显示得分，我们在alien_invasion.py中创建一个Scoreboard实例：
alien_invasion.py

import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类
from scoreboard import Scoreboard

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例,并创建记分牌
    stats = GameStats(ai_settings)
    sb = Scoreboard(ai_settings,screen,stats)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

     #   sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,stats,play_button,ship,aliens,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button)


run_game()

还需要修改update_screen()
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

运行游戏发现屏幕右上角显示0.

3.3 在外星人被消灭时更新得分

为在屏幕上实时地显示得分，每当有外星人被击中时，我们都更新stats.score的值，在调用prep_score()更新得分图像。
settings.py

class Settings():
    """存储<<外星人入侵>>的所有设置的类"""

    def __init__(self):
        """初始化游戏的设置"""
        #屏幕设置
        self.screen_width = 800
        self.screen_height = 600
        self.bg_color = (230,230,230)

        #飞船的设置
        self.ship_speed_factor = 1.5
        self.ship_limit = 3

        #子弹设置
        self.bullet_speed_factor = 3
        self.bullet_width = 3
        self.bullet_height = 15
        self.bullet_color = (60 , 60 , 60)
        self.bullets_allowed = 5   #将在屏幕内可以存在的子弹限制为3颗

        #外星人设置
        self.alien_speed_factor = 1
        self.fleet_drop_speed = 10

        #以什么样的速度加快游戏节奏
        self.speedup_scale = 1.1
        self.initialize_dynamic_settings()
        

    
    def initialize_dynamic_settings(self):
        """初始化随游戏进行而变化的设置"""

        #该方法设置了飞船、子弹和外星人的初始速度
        self.ship_speed_factor = 1.5
        self.bullet_speed_factor = 3
        self.alien_speed_factor = 1

        #fleet_direction为1表示向右移，为-1表示向左移
        self.fleet_direction = 1

        #计分
        self.alien_points = 50

    def increase_speed(self):
        """提高速度设置"""

        #使用该方法在玩家提高一个等级时，来提高飞船、子弹和外星人的速度
        self.ship_speed_factor *= self.speedup_scale
        self.bullet_speed_factor *= self.speedup_scale
        self.alien_speed_factor *=self.speedup_scale

也就是每击落一个外星人得50分。
在check_bullet_alien_collisions()中，每当有外星人被击落时，都更新得分：
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if collisions:
        stats.score += ai_settings.alien_points
        sb.prep_score()

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

有子弹撞到外星人时，Pygame返回一个字典(collisions)。然后检查这个字典是否存在，如果存在，就将得分加上一个外星人值的点数，接下来调用prep_score()来创建一副显示最新得分的新图像。
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if collisions:
        stats.score += ai_settings.alien_points
        sb.prep_score()

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

alien_invasion.py中也应该更新：

import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类
from scoreboard import Scoreboard

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例,并创建记分牌
    stats = GameStats(ai_settings)
    sb = Scoreboard(ai_settings,screen,stats)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

     #   sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,stats,play_button,ship,aliens,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button)


run_game()

3.4 将消灭的每个外星人的点数都计入得分

目前的计分值会遗漏被消灭的外星人。为了解决这个bug，我们来调整检测子弹和外星人碰撞的方式。
在check_bullet_alien_collisions()中，与外星人碰撞的子弹是字典collisions中的一个键；而与每颗子弹相关的值都是一个列表，其中包含该子弹撞到的外星人。我们遍历字典collisions，确保将消灭的每个外星人的点数都计入得分：
game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if collisions:
        for aliens in collisions.values():
            stats.score += ai_settings.alien_points
            sb.prep_score()

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

3.5 提高点数

settings.py

class Settings():
    """存储<<外星人入侵>>的所有设置的类"""

    def __init__(self):
        """初始化游戏的设置"""
        #屏幕设置
        self.screen_width = 800
        self.screen_height = 600
        self.bg_color = (230,230,230)

        #飞船的设置
        self.ship_speed_factor = 1.5
        self.ship_limit = 3

        #子弹设置
        self.bullet_speed_factor = 3
        self.bullet_width = 3
        self.bullet_height = 15
        self.bullet_color = (60 , 60 , 60)
        self.bullets_allowed = 5   #将在屏幕内可以存在的子弹限制为3颗

        #外星人设置
        self.alien_speed_factor = 1
        self.fleet_drop_speed = 10

        #以什么样的速度加快游戏节奏
        self.speedup_scale = 1.1

        #外星人点数的提高速度
        self.score_scale = 1.5

        self.initialize_dynamic_settings()
        

    
    def initialize_dynamic_settings(self):
        """初始化随游戏进行而变化的设置"""

        #该方法设置了飞船、子弹和外星人的初始速度
        self.ship_speed_factor = 1.5
        self.bullet_speed_factor = 3
        self.alien_speed_factor = 1

        #fleet_direction为1表示向右移，为-1表示向左移
        self.fleet_direction = 1

        #计分
        self.alien_points = 50

    def increase_speed(self):
        """提高速度设置"""

        #使用该方法在玩家提高一个等级时，来提高飞船、子弹和外星人的速度
        self.ship_speed_factor *= self.speedup_scale
        self.bullet_speed_factor *= self.speedup_scale
        self.alien_speed_factor *=self.speedup_scale

        self.alien_points = int(self.alien_points * self.score_scales)
        print(self.alien_points)

3.6 将得分圆整

大多数街机风格的射击游戏都将得分显示为10的整数倍，我们的计分系统也将遵循这个原则，在设置一些规则，在大数字中添加用逗号表示的千位分隔符，我们在scoreboard.py中修改
scoreboard.py

import pygame.font

class Scoreboard():
    """显示得分信息的类"""

    def __init__(self,ai_settings,screen,stats):
        """初始化显示得分涉及的属性"""

        self.screen  = screen
        self.screen_rect = screen.get_rect()
        self.ai_settings = ai_settings
        self.stats = stats

        #显示得分信息时使用的字体设置
        self.text_color = (30,30,30)
        self.font = pygame.font.SysFont(None,48)

        #准备初始得分图像
        self.prep_score()

    def prep_score(self):
        """将得分转换为一副渲染的图像"""
        rounded_score = int(round(self.stats.score, -1))
        score_str = "{:,}".format(rounded_score)
        #score_str = str(self.stats.score)
        self.score_image = self.font.render(score_str,True,self.text_color,self.ai_settings.bg_color)

        #将得分放在屏幕右上角
        self.score_rect = self.score_image.get_rect()
        self.score_rect.right = self.screen_rect.right - 20
        self.score_rect.top = 20

    def show_score(self):
        """在屏幕上显示得分"""
        self.screen.blit(self.score_image,self.score_rect)

注意：在python2.7中，round()总是返回一个小数值，因此我们使用int()来确保报告的得分为整数。如果在python3中，可省略对int()的调用

3.7 最高得分

我们将最高得分存储在GameStats中:
game_stats.py

class GameStats():
    """跟踪游戏的统计信息"""

    def __init__(self,ai_settings):
        """初始化统计信息"""
        self.ai_settings = ai_settings
        self.reset_stats()

        #游戏刚开始处于非活动状态
        self.game_active = False

        #在任何情况下都不应该重置最高得分
        self.high_score = 0

    def reset_stats(self):
        """初始化在游戏运行期间可能变化的统计信息"""
        self.ships_left = self.ai_settings.ship_limit
        self.score = 0

下面来修改Scoreboard以显示最高分
scoreboard.py

import pygame.font

class Scoreboard():
    """显示得分信息的类"""

    def __init__(self,ai_settings,screen,stats):
        """初始化显示得分涉及的属性"""

        self.screen  = screen
        self.screen_rect = screen.get_rect()
        self.ai_settings = ai_settings
        self.stats = stats

        #显示得分信息时使用的字体设置
        self.text_color = (30,30,30)
        self.font = pygame.font.SysFont(None,48)

        #准备初始得分图像
        self.prep_score()
        self.prep_high_score()

    def prep_score(self):
        """将得分转换为一副渲染的图像"""
        rounded_score = int(round(self.stats.score, -1))
        score_str = "{:,}".format(rounded_score)
        #score_str = str(self.stats.score)
        self.score_image = self.font.render(score_str,True,self.text_color,self.ai_settings.bg_color)

        #将得分放在屏幕右上角
        self.score_rect = self.score_image.get_rect()
        self.score_rect.right = self.screen_rect.right - 20
        self.score_rect.top = 20

    def show_score(self):
        """在屏幕上显示得分"""
        self.screen.blit(self.score_image,self.score_rect)
        self.screen.blit(self.high_score_image,self.high_score_rect)

    def prep_high_score(self):
        """将最高得分转换为渲染的图像"""
        high_score = int(round(self.stats.high_score, -1))
        high_score_str = "{:,}".format(high_score)
        self.high_score_image = self.font.render(high_score_str,True,self.text_color,self.ai_settings.bg_color)

        #将最高得分放在屏幕顶部*
        self.high_score_rect = self.high_score_image.get_rect()
        self.high_score_rect.centerx = self.screen_rect.centerx
        self.high_score_rect.top = self.score_rect.top

根据最高分生成一幅图像，使其水平居中，将其top属性设置为当前得分图像的top属性。
现在方法show_score()在屏幕右上角显示当前得分，并在屏幕顶部*显示最高得分。
为了检查是否诞生新的最高分，我们在game_functions.py中添加一个新函数check_high_score():
game_function.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if collisions:
        for aliens in collisions.values():
            stats.score += ai_settings.alien_points
            sb.prep_score()
        
        check_high_score(stats,sb)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()
        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        sys.exit(0)
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

def check_high_score(stats,sb):
    """检查是否诞生了新的最高分"""
    if stats.score > stats.high_score:
        stats.high_score = stats.score
        sb.prep_high_score()

3.8 显示等级

想要在游戏中显示玩家的等级，需要在GameStats中添加一个表示当前等级的属性。为确保每次开始新游戏时都重置等级，在reset_stats()中初始化它：
game_stats.py

class GameStats():
    """跟踪游戏的统计信息"""

    def __init__(self,ai_settings):
        """初始化统计信息"""
        self.ai_settings = ai_settings
        self.reset_stats()

        #游戏刚开始处于非活动状态
        self.game_active = False

        #在任何情况下都不应该重置最高得分
        self.high_score = 0


    def reset_stats(self):
        """初始化在游戏运行期间可能变化的统计信息"""
        self.ships_left = self.ai_settings.ship_limit
        self.score = 0
        self.level = 1

    

scoreboard.py

import pygame.font

class Scoreboard():
    """显示得分信息的类"""

    def __init__(self,ai_settings,screen,stats):
        """初始化显示得分涉及的属性"""

        self.screen  = screen
        self.screen_rect = screen.get_rect()
        self.ai_settings = ai_settings
        self.stats = stats

        #显示得分信息时使用的字体设置
        self.text_color = (30,30,30)
        self.font = pygame.font.SysFont(None,48)

        #准备初始得分图像
        self.prep_score()
        self.prep_high_score()
        self.prep_level()

    def prep_score(self):
        """将得分转换为一副渲染的图像"""
        rounded_score = int(round(self.stats.score, -1))
        score_str = "{:,}".format(rounded_score)
        #score_str = str(self.stats.score)
        self.score_image = self.font.render(score_str,True,self.text_color,self.ai_settings.bg_color)

        #将得分放在屏幕右上角
        self.score_rect = self.score_image.get_rect()
        self.score_rect.right = self.screen_rect.right - 20
        self.score_rect.top = 20

    def show_score(self):
        """在屏幕上显示得分"""
        self.screen.blit(self.score_image,self.score_rect)
        self.screen.blit(self.high_score_image,self.high_score_rect)
        self.screen.blit(self.level_image,self.level_rect)

    def prep_high_score(self):
        """将最高得分转换为渲染的图像"""
        high_score = int(round(self.stats.high_score, -1))
        high_score_str = "{:,}".format(high_score)
        self.high_score_image = self.font.render(high_score_str,True,self.text_color,self.ai_settings.bg_color)

        #将最高得分放在屏幕顶部*
        self.high_score_rect = self.high_score_image.get_rect()
        self.high_score_rect.centerx = self.screen_rect.centerx
        self.high_score_rect.top = self.score_rect.top

    def prep_level(self):
        """将等级转换为渲染的图像"""
        self.level_image = self.font.render(str(self.stats.level),True,self.text_color,self.ai_settings.bg_color)

        #将等级放在得分下方
        self.level_rect = self.level_image.get_rect()
        self.level_rect.right= self.score_rect.right
        self.level_rect.top = self.score_rect.bottom + 10

game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)

def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, sb,play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,sb,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,sb,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #重置记分牌图像
        sb.prep_score()
        sb.prep_high_score()
        sb.prep_level()

        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if collisions:
        for aliens in collisions.values():
            stats.score += ai_settings.alien_points
            sb.prep_score()
        
        check_high_score(stats,sb)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()

        stats.level += 1
        sb.prep_level()

        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,ship,aliens):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        print("Ship hit!!!")

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        #sys.exit(0)
        stats.game_active = False
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,ship,aliens,bullets)

def check_high_score(stats,sb):
    """检查是否诞生了新的最高分"""
    if stats.score > stats.high_score:
        stats.high_score = stats.score
        sb.prep_high_score()

alien_invasion.py

import sys
import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类
from scoreboard import Scoreboard

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例,并创建记分牌
    stats = GameStats(ai_settings)
    sb = Scoreboard(ai_settings,screen,stats)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

        #sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,stats,sb,play_button,ship,aliens,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button)


run_game()

4.9 显示余下的飞船数

最后，我们来显示玩家还有多少艘飞船，使用图形的方式，为此，我们需要在屏幕左上角绘制飞船图像来指出还余下多少艘飞船。
ship.py

import pygame
from pygame.sprite import Sprite

class Ship(Sprite):

    def __init__(self,ai_settings,screen):
        """初始化飞船并设置其初始化位置"""
        super(Ship,self).__init__()
        self.screen = screen
        self.ai_settings = ai_settings

        #加载飞船图像并获取其外接矩形
        self.image = pygame.image.load('images/ship.bmp')
        self.rect = self.image.get_rect()
        self.screen_rect = screen.get_rect()

        #将每艘新飞船放在屏幕底部*
        self.rect.centerx = self.screen_rect.centerx
        self.rect.bottom = self.screen_rect.bottom

        #在飞船的属性center中存储小数值
        self.center = float(self.rect.centerx)

        #移动标志
        self.moving_right = False
        self.moving_left = False
        self.moving_up = False
        self.moving_down = False

    def update(self):
        """根据移动标志调整飞船的位置"""
        #更新飞船的center值，而不是rect
        if self.moving_right and self.rect.right < self.screen_rect.right:
            self.center += self.ai_settings.ship_speed_factor
        elif self.moving_left and self.rect.left > 0:
            self.center -= self.ai_settings.ship_speed_factor
        elif self.moving_up and self.rect.up < self.screen_rect.up:
            self.center += self.ai_settings.ship_speed_factor
        elif self.moving_down and self.rect.down > 0:
            self.center -= self.ai_settings.ship_speed_factor

        #根据self.center更新rect对象
        self.rect.centerx = self.center

    def blitme(self):
        """在指定位置绘制飞船"""
        self.screen.blit(self.image,self.rect)

    def center_ship(self):
        """让飞船在屏幕上居中"""
        self.center = self.screen_rect.centerx

scoreboard.py

import pygame.font
from pygame.sprite import Group
from ship import Ship

class Scoreboard():
    """显示得分信息的类"""

    def __init__(self,ai_settings,screen,stats):
        """初始化显示得分涉及的属性"""

        self.screen  = screen
        self.screen_rect = screen.get_rect()
        self.ai_settings = ai_settings
        self.stats = stats

        #显示得分信息时使用的字体设置
        self.text_color = (30,30,30)
        self.font = pygame.font.SysFont(None,48)

        #准备初始得分图像
        self.prep_score()
        self.prep_high_score()
        self.prep_level()
        self.prep_ships()

    def prep_score(self):
        """将得分转换为一副渲染的图像"""
        rounded_score = int(round(self.stats.score, -1))
        score_str = "{:,}".format(rounded_score)
        #score_str = str(self.stats.score)
        self.score_image = self.font.render(score_str,True,self.text_color,self.ai_settings.bg_color)

        #将得分放在屏幕右上角
        self.score_rect = self.score_image.get_rect()
        self.score_rect.right = self.screen_rect.right - 20
        self.score_rect.top = 20

    def show_score(self):
        """在屏幕上显示得分"""
        self.screen.blit(self.score_image,self.score_rect)
        self.screen.blit(self.high_score_image,self.high_score_rect)
        self.screen.blit(self.level_image,self.level_rect)
        #绘制飞船
        self.ships.draw(self.screen)

    def prep_high_score(self):
        """将最高得分转换为渲染的图像"""
        high_score = int(round(self.stats.high_score, -1))
        high_score_str = "{:,}".format(high_score)
        self.high_score_image = self.font.render(high_score_str,True,self.text_color,self.ai_settings.bg_color)

        #将最高得分放在屏幕顶部*
        self.high_score_rect = self.high_score_image.get_rect()
        self.high_score_rect.centerx = self.screen_rect.centerx
        self.high_score_rect.top = self.score_rect.top

    def prep_level(self):
        """将等级转换为渲染的图像"""
        self.level_image = self.font.render(str(self.stats.level),True,self.text_color,self.ai_settings.bg_color)

        #将等级放在得分下方
        self.level_rect = self.level_image.get_rect()
        self.level_rect.right= self.score_rect.right
        self.level_rect.top = self.score_rect.bottom + 10

    #该方法创建一个空的编组self.ships,用于存储飞船的实例
    def prep_ships(self):
        """显示还余下多少艘飞船"""
        self.ships = Group()
        for ship_number in range(self.stats.ship_left):
            ship = Ship(self.ai_settings,self.screen)
            ship.rect.x = 10 + ship_number * ship,rect.width
            ship.rect.y = 10
            self.ships.add(ship)

game_functions.py

import sys
import pygame
from bullet import Bullet
from alien import Alien
from time import sleep

def check_keydown_events(event,ai_settings,screen, stats,ship,bullets):
    """响应按键"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = True
    elif event.key == pygame.K_LEFT:
        ship.moving_left = True
    elif event.key == pygame.K_SPACE:
       fire_bullet(ai_settings,screen,ship,bullets)
    elif event.key == pygame.K_q:
        sys.exit(0)
    elif event.key == pygame.K_p:
        stats.game_active = True


def check_keyup_events(event,ship):
    """响应松开"""
    if event.key == pygame.K_RIGHT:
        ship.moving_right = False
    if event.key == pygame.K_LEFT:
        ship.moving_left = False

def check_events(ai_settings,screen, stats, sb,play_button,ship,aliens,bullets):
    """响应按键和鼠标事件"""
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit(0)  #在这里的exit()中需要传递参数，他么的，竟然这么坑吗？
        elif event.type == pygame.KEYDOWN:
             check_keydown_events(event, ai_settings,screen,stats,ship, bullets)
        elif event.type == pygame.KEYUP:
            check_keyup_events(event,ship)
        elif event.type == pygame.MOUSEBUTTONDOWN:
            mouse_x, mouse_y = pygame.mouse.get_pos()
            check_play_button(ai_settings,screen,stats,sb,play_button,ship,aliens,bullets,mouse_x,mouse_y)

def check_play_button(ai_settings,screen,stats,sb,play_button,ship,aliens,bullets,mouse_x,mouse_y):
    """在玩家单击Play按钮时开始游戏"""
    
    button_clicked = play_button.rect.collidepoint(mouse_x,mouse_y)
    if button_clicked and not stats.game_active:

        #重置游戏设置
        ai_settings.initialize_dynamic_settings()

        #隐藏光标
        pygame.mouse.set_visible(False)
        #重置游戏统计信息
        stats.reset_stats()
        stats.game_active = True
        
        #重置记分牌图像
        sb.prep_score()
        sb.prep_high_score()
        sb.prep_level()
        sb.prep_ships()

        #清空外星人列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群新的外星人，并让飞船居中
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()
                
def update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button):
    """更新屏幕上的图像，并切换到新屏幕"""

    #每次循环时都重绘屏幕
    screen.fill(ai_settings.bg_color)
     #在飞船和外星人后面重绘所有子弹
    for bullet in bullets.sprites():
        bullet.draw_bullet()
    ship.blitme()
    aliens.draw(screen)

    #显示得分
    sb.show_score()

    #如果游戏处于非活动状态，就绘制Play按钮
    if not stats.game_active:
        play_button.draw_button()

    #让最近绘制的屏幕可见
    pygame.display.flip()

def update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """更新子弹的位置，并删除已销失的子弹"""

    #更新子弹的位置
    bullets.update()

    #删除已销失的子弹
    for bullet in bullets.copy():
        if bullet.rect.bottom <= 0:
            bullets.remove(bullet)

    if len(bullets) != 0:
        print(len(bullets))

    #检查是否有子弹击中了外星人
    #如果这样，就删除相应的子弹和外星人
    check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets)

def check_bullet_alien_collisions(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """响应子弹和外星人的碰撞"""
    #删除发生碰撞的子弹和外星人
    collisions = pygame.sprite.groupcollide(bullets,aliens,True,True)

    if collisions:
        for aliens in collisions.values():
            stats.score += ai_settings.alien_points
            sb.prep_score()
        
        check_high_score(stats,sb)

    if len(aliens) == 0:
        #删除现有的子弹并新建一群外星人
        #删除现有的子弹，加快游戏节奏，并创建一群新的外星人
        bullets.empty()
        ai_settings.increase_speed()

        stats.level += 1
        sb.prep_level()

        create_fleet(ai_settings,screen,ship,aliens)

def fire_bullet(ai_settings,screen,ship,bullets):
    """如果还没有到达限制，就发射一颗子弹"""

    #创建新子弹，并将其加入到编组bullets中
    if len(bullets) < ai_settings.bullets_allowed:
        new_bullet = Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def get_number_aliens_x(ai_settings,alien_width):
    """计算每行可容纳多少外星人"""
    available_space_x = ai_settings.screen_width - 2 * alien_width
    number_alien_x = int(available_space_x / (2 * alien_width))
    return number_alien_x

def get_number_rows(ai_settings,ship_height,alien_height):
    """计算屏幕可容纳多少行外星人"""
    available_space_y = (ai_settings.screen_height - (3 * alien_height) - ship_height)
    number_rows = int(available_space_y / (2 * alien_height))
    return number_rows

def create_alien(ai_settings,screen,aliens,alien_number,row_number):
    """创建一个外星人并将其加入当前行"""

    alien = Alien(ai_settings,screen)
    alien_width = alien.rect.width
    alien.x = alien_width + 2 * alien_width * alien_number
    alien.rect.x = alien.x
    alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
    aliens.add(alien)

def create_fleet(ai_settings,screen,ship,aliens):
    """创建外星人"""
    #创建一个外星人，并计算一行可容纳多少外星人
    #外星人间距为外星人宽度
    alien = Alien(ai_settings,screen)
    number_aliens_x = get_number_aliens_x(ai_settings,alien.rect.width)
    number_rows = get_number_rows(ai_settings,ship.rect.height,alien.rect.height)

    #创建第一行外星人
    for row_number in range(number_rows):
        for alien_number in range(number_aliens_x):
            create_alien(ai_settings,screen,aliens,alien_number,row_number)

def update_aliens(ai_settings,screen,stats,sb,ship,aliens,bullets):
    """更新外星人群中所有外星人的位置"""
    aliens.update()

    #检测外星人和飞船之间的碰撞
    if pygame.sprite.spritescollideany(ship,aliens):
        ship_hit(ai_settings,screen,stats,sb,ship,aliens,bullets)
        print("Ship hit!!!")
    
    check_aliens_bottom(ai_settings,screen,stats,sb, ship,aliens,bullets)

def check_fleet_edges(ai_settings,aliens):
    """有外星人到达边缘时采取相应的措施"""
    for alien in aliens.sprites():
        if alien.check_edges():
            change_fleet_direction(ai_settings,aliens)
            break

def change_fleet_direction(ai_settings,aliens):
    """将整群外星人下移，并改变它们的方向"""

    for alien in aliens.sprites():
        alien.rect.y += ai_settings.fleet_drop_speed
    ai_settings.fleet_direction *= -1

def ship_hit(ai_settings,stats,screen,sb,ship,aliens,bullets):
    """相应被外星人撞到的飞船"""
    if stats.ships_left > 0:
        #将ships_left 减1
        stats.ships_left -= 1

        #更新记分牌
        sb.prep_ships()

        #清空外星人到列表和子弹列表
        aliens.empty()
        bullets.empty()

        #创建一群外星人，并将飞船放到屏幕底端*
        create_fleet(ai_settings,screen,ship,aliens)
        ship.center_ship()

        #暂停
        sleep(0.5)
        #sys.exit(0)
        #stats.game_active = False
    else:
        stats.game_active = False
        pygame.mouse.set_visible(True)

def check_aliens_bottom(ai_settings,stats,screen,sb,ship,aliens,bullets):
    """检查是否有外星人到达了屏幕底端"""
    screen_rect = screen.get_rect()
    for alien in aliens.sprites():
        if alien.rect.bottom >= screen_rect.bottom:
            #像飞船被撞到一样进行处理
            ship_hit(ai_settings,stats,screen,sb,ship,aliens,bullets)
            break

def update_aliens(ai_settings,stats,screen,sb,ship,aliens,bullets):
    """检查是否有外星人位于屏幕边缘，并更新整群外星人的位置"""

    check_fleet_edges(ai_settings,aliens)
    aliens.update()

    if pygame.sprite.spritecollideany(ship,aliens):
        ship_hit(ai_settings,stats,screen,sb,ship,aliens,bullets)

    #检查是否有外星人到达屏幕底端
    check_aliens_bottom(ai_settings,stats,screen,sb,ship,aliens,bullets)

def check_high_score(stats,sb):
    """检查是否诞生了新的最高分"""
    if stats.score > stats.high_score:
        stats.high_score = stats.score
        sb.prep_high_score()

alien_invasion.py

import sys
import pygame
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf
from pygame.sprite import Group
from button import Button  #导入button类
from scoreboard import Scoreboard

def run_game():
    #初始化游戏并创建一个屏幕对象
    pygame.init()
    ai_settings = Settings()
    screen = pygame.display.set_mode((ai_settings.screen_width,ai_settings.screen_height))
    pygame.display.set_caption("Alien Invasion")

    #创建Play按钮,并创建一个button实例
    play_button = Button(ai_settings,screen,"play") 

    #创建一个外星人
    alien = Alien(ai_settings,screen)

    #创建一个用于存储游戏统计信息的实例,并创建记分牌
    stats = GameStats(ai_settings)
    sb = Scoreboard(ai_settings,screen,stats)

    #创建一艘非飞船
    ship = Ship(ai_settings,screen)
    #创建一个用于存储子弹的编组
    bullets = Group()
    aliens = Group()

    #创建外星人群
    gf.create_fleet(ai_settings,screen,ship,aliens)

    #开始游戏的主循环
    while True:

        #sys.pause()
        #监视键盘和鼠标事件
        gf.check_events(ai_settings,screen,stats,sb,play_button,ship,aliens,bullets)
        if stats.game_active:
            ship.update()
            gf.update_bullets(ai_settings,screen,stats,sb,ship,aliens,bullets)
            gf.update_aliens(ai_settings,stats,screen,sb,ship,aliens,bullets)
        
        gf.update_screen(ai_settings,screen,stats,sb,ship,bullets,aliens,play_button)


run_game()