飞船撞击到外星人后，返回不了底部中央，只能手动设置参数，明天好好研究一下

alien_invasion.py

import sys

import pygame

from pygame.sprite import Group
from settings import Settings
from game_stats import GameStats
from ship import Ship
from alien import Alien
import game_functions as gf

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")

	#创建一个用于存储游戏统计信息的实例
	stats = GameStats(ai_settings)
	#创建一艘飞船
	ship = Ship(ai_settings, screen)
	#创建一个存储子弹的编组
	bullets = Group()
	#创建一个外星人编组
	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:
		gf.check_events(ai_settings, screen, ship, bullets)
		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, ship, aliens, bullets)

run_game()

game_functions.py

import sys
from time import sleep

import pygame

from bullet import Bullet
from alien import Alien


def check_keydown_event(event, ai_settings, screen, ship, bullets):
	#相应按键
	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_UP:
		ship.moving_up = True
	elif event.key == pygame.K_DOWN:
		ship.moving_down = True
	elif event.key == pygame.K_SPACE:
		#创建一颗子弹，并将其加入到编组bullets中
		fire_bullet(ai_settings, screen, ship, bullets)
	elif event.key == pygame.K_q:
		sys.exit()
		
def check_keyup_event(event, ship):
	if event.key == pygame.K_RIGHT:
		ship.moving_right = False
	elif event.key == pygame.K_LEFT:
		ship.moving_left = False
	if event.key == pygame.K_UP:
		ship.moving_up = False
	elif event.key == pygame.K_DOWN:
		ship.moving_down = False

def check_events(ai_settings, screen, ship, bullets):
	#监视键盘和鼠标事件
	for event in pygame.event.get():
		if event.type == pygame.QUIT:
			sys.exit()
		elif event.type == pygame.KEYDOWN:
			check_keydown_event(event, ai_settings, screen, ship, bullets)
		elif event.type == pygame.KEYUP:
			check_keyup_event(event, ship)

def update_bullets(ai_settings, screen, ship, aliens, bullets):
	#更新子弹的位置，并删除已消失的子弹
	bullets.update()

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

	check_bullet_alien_collisions(ai_settings, screen, ship, aliens, bullets)

def check_bullet_alien_collisions(ai_settings, screen, ship, aliens, bullets):
	#相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:
		#删除现有的所有子弹，并新创建一个新的外星人群
		bullets.empty()
		create_fleet(ai_settings, screen, ship, aliens)

def fire_bullet(ai_settings, screen, ship, bullets):
	#如果还没有达到限制，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 update_screen(ai_settings, screen, ship, aliens, bullets):
	#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:
		bullet.draw_bullet()#子弹绘制
	ship.blitme()
	aliens.draw(screen)

	#让最近绘制的屏幕可见
	pygame.display.flip()

def get_number_aliens_x(ai_settings, alien_width):
	#计算可容纳多少个外星人
	available_space_x = ai_settings.screen_width - 2 * alien_width
	number_aliens_x = int(available_space_x / (2 * alien_width))
	return number_aliens_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放在当前行
	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):
	#创建外星人群
	#创建一个外星人，并计算一行可容纳多少个外星人
	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)

	#创建外星人群
	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 check_fleet_edges(ai_settings, aliens):
	#有外星人到达边缘时采取的措施
	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其方向
	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):
	#响应被外星人撞到的飞船
	#将ships_left减1
	stats.ships_left -= 1

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

	#暂停
	sleep(0.5)

	#创建一群新的外星人，并将飞船放在屏幕底端中央
	create_fleet(ai_settings, screen, ship, aliens)
	ship.center_ship()

def update_aliens(ai_settings, stats, screen, ship, aliens,bullets):
	#检查是否有外星人位于屏幕边缘，然后更新所有外星人群的位置
	check_fleet_edges(ai_settings, aliens)
	aliens.update()

	#检测外星人和飞船之间的碰撞
	if pygame.sprite.spritecollideany(ship, aliens):
		ship_hit(ai_settings, stats, screen, ship, aliens, bullets)

settings.py

class Settings():
	#《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 = 1200
		self.screen_height = 700
		self.bg_color = (255, 192, 203)

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

		#外星人设置
		self.alien_speed_factor = 1
		self.fleet_drop_speed = 10
		#fleet_direction为1表示向右移，为-1表示向左移
		self.fleet_direction = 1

		#子弹设置
		self.bullet_speed_factor = 3
		self.bullet_width = 300
		self.bullet_height = 15
		self.bullet_color = 60, 60, 60
		self.bullets_allowed = 3

ship.py

import pygame

class Ship():

	def __init__(self, ai_settings, screen):
		#初始化飞船并设置其初始位置
		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()

		#将每艘飞船放在屏幕底中央
		self.rect.centerx = self.screen_rect.centerx
		self.rect.centery = self.screen_rect.centery
		self.rect.bottom = self.screen_rect.bottom

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

		#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.centerx += self.ai_settings.ship_speed_factor
		if self.moving_left and self.rect.left > 0:
			self.centerx -= self.ai_settings.ship_speed_factor
		if self.moving_up and self.rect.top > self.screen_rect.top:
			self.centery -= self.ai_settings.ship_speed_factor
		if self.moving_down and self.rect.bottom < self.screen_rect.bottom:
			self.centery += self.ai_settings.ship_speed_factor
		#根据self.center更新rect对象
		self.rect.centerx = self.centerx
		self.rect.centery = self.centery

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

	def center_ship(self):
		self.centerx = float(600)
		self.centery = float(675)

alien.py

import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
	#表示单个外星人的类

	def __init__(self, ai_settings, screen):
		#初始化外星人并设置其起始位置
		super(Alien, self).__init__()
		self.screen = screen
		self.ai_settings = ai_settings

		#加载外星人图像，并设置其rect属性
		self.image = pygame.image.load('images/alien.bmp')
		self.rect = self.image.get_rect()

		#每个外星人最初都在屏幕左上角附近
		self.rect.x = self.rect.width
		self.rect.y = self.rect.height

		#存储外星人的准确位置
		self.x = float(self.rect.x)

	def blitme(self):
		#在指定位置绘制外星人
		self.screen.blit(self.image, self.rect)

	def check_edges(self):
		#如果外星人位于屏幕边缘，就返回True
		screen_rect = self.screen.get_rect()
		if self.rect.right >= screen_rect.right:
			return True
		elif self.rect.left <= 0:
			return True

	def update(self):
		#向左或向右移动外星人
		self.x += (self.ai_settings.alien_speed_factor *
						self.ai_settings.fleet_direction)
		self.rect.x = self.x

bullet.py

import pygame
from pygame.sprite import Sprite

class Bullet(Sprite):
	#一个对飞船发射的子弹进行管理的类

	def __init__(self, ai_settings, screen, ship):
		#在飞船所处位置创建一个子弹对象
		super(Bullet, self).__init__()
		self.screen = screen

		#在(0,0)处创建一个表示子弹的矩形，再设置正确的位置
		self.rect = pygame.Rect(0, 0, ai_settings.bullet_width,
			ai_settings.bullet_height)
		self.rect.centerx = ship.rect.centerx
		self.rect.top = ship.rect.top

		#存储用小数点表示的子弹位置
		self.y = float(self.rect.y)

		self.color = ai_settings.bullet_color
		self.speed_factor = ai_settings.bullet_speed_factor

	def update(self):
		#向上移动子弹
		#更新表示子弹位置的小数值
		self.y -= self.speed_factor
		#更新表示子弹的rect位置
		self.rect.y = self.y

	def draw_bullet(self):
		#在屏幕上绘制子弹
		pygame.draw.rect(self.screen, self.color, self.rect)

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()

	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

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原文链接：飞船撞击到外星人后，返回不了底部中央，只能手动设置参数，明天好好研究一下，转载请注明来源！