ship.py

import pygame
from pygame.sprite import Sprite

class Ship(Sprite):

    def __init__(self, ui_settings, screen):
        ''' Initalize the ship and set its starting position '''
        super(Ship, self).__init__()
        self.screen = screen
        self.ui_settings = ui_settings

        # Load the ship image and get its rect
        self.image = pygame.image.load('images/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 movement flags '''
        if self.moving_right and self.rect.right < self.screen_rect.right:
            self.center += self.ui_settings.ship_speed_factor
        if self.moving_left and self.rect.left > 0:
            self.center -= self.ui_settings.ship_speed_factor

        # Update the 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