ship.py

import pygame
from pygame.sprite import Sprite 

class Ship(Sprite):
    """A class to manage the SpaceShip"""

    def __init__(self, ai_game):
        """initialize spaceship and set its starting position"""

        super().__init__()
        self.screen = ai_game.screen
        self.settings = ai_game.settings
        self.screen_rect = ai_game.screen.get_rect()

        # Load the image and get its rect
        self.image = pygame.image.load('ship2.png')
        self.rect = self.image.get_rect()

        # start each new ship at the bottom centre of the screen 
        self.rect.midbottom = self.screen_rect.midbottom 

        # store a float for the ship's exact horizontal position 
        self.x = float(self.rect.x)

        # movement flags; start with a ship that's not moving 
        self.moving_right = False
        self.moving_left = False

    def update(self) :
        """update the ship's position based on the movement flag"""
        # update ship's x value, not the rect.
        if self.moving_right and self.rect.right < self.screen_rect.right :
            self.x += self.settings.ship_speed
        if self.moving_left and self.rect.left>0 :
            self.x -= self.settings.ship_speed
        # update rect object from self.x
        self.rect.x = self.x

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

    def center_ship(self):
        """center the ship on the screen"""
        self.rect.midbottom = self.screen_rect.midbottom
        self.x = float(self.rect.x)