alien.py

import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
	"""A class to represent a single aalien in the fleet"""

	def __init__(self,ai_game):
		"""Initialize the alien and set it's starting position"""
		super().__init__()
		self.screen = ai_game.screen
		self.settings = ai_game.settings

		#Load the alien image and set it's 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 horizontal position
		self.x = float(self.rect.x)

	#Update Alien
	def update(self):
		"""Move the alien to the right or left"""
		self.x += (self.settings.alien_speed *
			self.settings.fleet_direction)
		self.rect.x = self.x


	#Check if alien hits edges of the screen
	def check_edges(self):
		"""Return True if alien is at edge of the screen"""
		screen_rect = self.screen.get_rect()

		if self.rect.right >= screen_rect.right or self.rect.left <= 0:
			return True