bullet.py

import pygame
from pygame.sprite import Sprite

class Bullet(Sprite):
	"""A class to manage bullets fired from the ship"""
	def __init__(self,ai_game):
		"""Create a bullet object at the ship's current position"""
		super().__init__()
		self.screen   = ai_game.screen
		self.settings = ai_game.settings
		self.color	  = self.settings.bullet_color

		#Create a rect(0,0) and then set correct position.
		self.rect = pygame.Rect(0,0, self.settings.bullet_width,
			self.settings.bullet_height)
		self.rect.midtop = ai_game.ship.rect.midtop

		#Store the bullet's position as a decimal
		self.y = float(self.rect.y)

	def update(self):
		"""Move the bullet up the screen"""
		#Update the decimal position of the bullet.
		self.y -= self.settings.bullet_speed
		#Update the rect position
		self.rect.y = self.y

	def draw_bullet(self):
		"""Draw the bullet to the screen"""
		pygame.draw.rect(self.screen,self.color,self.rect)