Python Programming: From Beginner to Practice, Chapters 12–14: Source Code for the 2D Game 'Space Invaders'.

    #!/usr/bin/python
    # -*- coding:utf8 -*-
    
    import sys
    import pygame
    from pygame.sprite import  Group
    
    from settings import Settings
    from game_stats import GameStats
    from scoreboard import Scoreboard
    from button import Button
    from ship import Ship
    from al