ship.py

import pygame
from pygame.sprite import Sprite

class Ship(Sprite):
    def __init__(self,ai_settings,screen):
        """"Initialize the ship and set its starting position."""
        super(Ship,self).__init__()
        self.screen=screen
        self.ai_settings=ai_settings
         
        #load the ship image and get its rect.
        self.image=pygame.image.load('ship.bmp')
        self.rect=self.image.get_rect()
        self.screen_rect=screen.get_rect()

        #Start each new ship at the bottom center of the screen.
        self.rect.centerx=self.screen_rect.centerx
        self.rect.bottom=self.screen_rect.bottom

        #Store a decimal value for the ship's center.
        self.center=float(self.rect.centerx)

        #Movement flag
        self.moving_right=False
        self.moving_left=False

    def update(self):
        """Update the ship's position based on the movement flag."""
        if self.moving_right and self.rect.right<self.screen_rect.right:
            self.center += self.ai_settings.ship_speed_factor
        if self.moving_left and self.rect.left>0:
            self.center -= self.ai_settings.ship_speed_factor
        #update rect object from self.center.
        self.rect.centerx=self.center

    def blitme(self):
        """Draw the ship at its current location."""
        self.screen.blit(self.image,self.rect)

    def center_ship(self):
        """Center the ship on the screen."""
        self.center=self.screen_rect.centerx