bullet.py

import pygame
from pygame.sprite import Sprite

class Bullet(Sprite):       #When you use sprites, you can group related elements in your game and act on all the grouped elements at once. 
    """A class to manage bullets fired from the ship"""
    
    def __init__(self, ai_settings, screen, ship):
        """Create a bullet object at the ship's current position."""
    
        super(Bullet, self).__init__()      #or, super().__init__()
        self.screen = screen

        # Create a bullet rect at (0, 0) and then set correct position.
        self.rect = pygame.Rect(0, 0, ai_settings.bullet_width,
        ai_settings.bullet_height)
        self.rect.centerx = ship.rect.centerx       
        self.rect.top = ship.rect.top

        # Store the bullet's position as a decimal value.
        self.y = float(self.rect.y)
        self.color = ai_settings.bullet_color
        self.speed_factor = ai_settings.bullet_speed_factor
    
    
    def update(self):
        """Move the bullet up the screen."""
        
        # Update the decimal position of the bullet.
        self.y -= self.speed_factor
    
        # 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)