alien.py

import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
    ''' A class to represent a single alien in the fleet '''

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

        # Load the alien image and set its rect attribute
        self.image = pygame.image.load('images/alien.bmp')
        self.rect = self.image.get_rect()

        # Start each new alien near the top left of the screen
        self.rect.x = self.rect.width
        self.rect.y = self.rect.height

        # Store the alien's exact position
        self.x = float(self.rect.x)

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

    def update(self):
        ''' Move the alien left or right '''
        self.x += self.ui_settings.alien_speed_factor * self.ui_settings.fleet_direction
        self.rect.x = self.x

    def check_edges(self):
        ''' Return True if alien is at edge of screen '''
        screen_rect = self.screen.get_rect()
        if self.rect.right >= screen_rect.right:
            return True
        elif self.rect.left <= 0:
            return True