解决了飞船上下左右边界移动问题

解决了昨天遗留的飞船上下移动报错的问题：
alian_invation.py

import sys

import pygame

from settings import Settings
from ship import Ship
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("Alian Invasion")

	#创建一艘飞船
	ship = Ship(ai_settings, screen)

	#开始游戏的主循环
	while True:
		gf.check_events(ship)
		ship.update()
		gf.update_screen(ai_settings, screen, ship)

run_game()

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

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/handsome.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)

game_functions.py

import sys

import pygame

def check_keydown_event(event, ship):
	#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

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(ship):
	#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, ship)
		elif event.type == pygame.KEYUP:
			check_keyup_event(event, ship)
 
def update_screen(ai_settings, screen, ship):
    #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)
	ship.blitme()
	#让最近绘制的屏幕可见
	pygame.display.flip()