game_functions.py

import sys
import pygame
from pygame.sprite import Group
from bullet import Bullet

def check_keydown_events(event,ai_settings,screen,ship,bullets):
    if event.key==pygame.K_RIGHT:
        ship.moving_right=True
    elif event.key==pygame.K_LEFT:
        ship.moving_left=True
    elif event.key==pygame.K_SPACE:
        fire_bullet(ai_settings,screen,ship,bullets)

def fire_bullet(ai_settings,screen,ship,bullets):
    """Fire a bullet if limit not reached yet."""
   #create a new bullet and add it to bullets group.
    if len(bullets)<ai_settings.bullets_allowed:
        new_bullet=Bullet(ai_settings,screen,ship)
        bullets.add(new_bullet)

def check_keyup_events(event,ship):
    if event.key==pygame.K_RIGHT:
        ship.moving_right=False
    elif event.key==pygame.K_LEFT:
        ship.moving_left=False

def check_events(ai_settings,screen,ship,bullets):
    """Respond to keypresses and mouse events."""
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            sys.exit()
        elif event.type==pygame.KEYDOWN:
            check_keydown_events(event,ai_settings,screen,ship,bullets)
        elif event.type==pygame.KEYUP:
            check_keyup_events(event,ship)

def update_screen(ai_settings,screen,ship,bullets):
   """update images on the screen and flip to the new screen."""
   #redraw the screen during each pass through the loop.
   screen.fill(ai_settings.bg_color)
   #redraw all bullets behind ship and aliens.
   for bullet in bullets.sprites():
       bullet.draw_bullet()
   ship.blitme()

   #Make the most recently drawn screen visible.
   pygame.display.flip()

def update_bullets(bullets):
    """update position of bullets and get rid of old bullets."""
    #update bullet positions.
    bullets.update()
    #get rid of bullets that have disappeared
    for bullet in bullets.copy():
        if bullet.rect.bottom<=0:
            bullets.remove(bullet)