Space Shooter made using Pygame

Question

This is my first game made using Pygame of about 550 lines of code. Advice and suggestions are more than welcome.

## Game music Attribution
##Frozen Jam by tgfcoder <https://twitter.com/tgfcoder> licensed under CC-BY-3 <http://creativecommons.org/licenses/by/3.0/>

from __future__ import division
import pygame
import random
from os import path

## assets folder
img_dir = path.join(path.dirname(__file__), 'assets')
sound_folder = path.join(path.dirname(__file__), 'sounds')

###############################
## to be placed in "constant.py" later
WIDTH = 480
HEIGHT = 600
FPS = 60
POWERUP_TIME = 5000

# Define Colors 
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)
YELLOW = (255, 255, 0)
###############################

###############################
## to placed in "__init__.py" later
## initialize pygame and create window
pygame.init()
pygame.mixer.init()  ## For sound
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Space Shooter")
clock = pygame.time.Clock()     ## For syncing the FPS
###############################

font_name = pygame.font.match_font('arial')

def main_menu():
    global screen

    menu_song = pygame.mixer.music.load(path.join(sound_folder, "menu.ogg"))
    pygame.mixer.music.play(-1)

    title = pygame.image.load(path.join(img_dir, "main.png")).convert()
    title = pygame.transform.scale(title, (WIDTH, HEIGHT), screen)

    screen.blit(title, (0,0))
    pygame.display.update()

    while True:
        ev = pygame.event.poll()
        if ev.type == pygame.KEYDOWN:
            if ev.key == pygame.K_RETURN:
                break
            elif ev.key == pygame.K_q:
                pygame.quit()
                quit()
        else:
            draw_text(screen, "Press [ENTER] To Begin", 30, WIDTH/2, HEIGHT/2)
            draw_text(screen, "or [Q] To Quit", 30, WIDTH/2, (HEIGHT/2)+40)
            pygame.display.update()

    #pygame.mixer.music.stop()
    ready = pygame.mixer.Sound(path.join(sound_folder,'getready.ogg'))
    ready.play()
    screen.fill((0,0,0))
    draw_text(screen, "GET READY!", 40, WIDTH/2, HEIGHT/2)
    pygame.display.update()


def draw_text(surf, text, size, x, y):
    ## selecting a cross platform font to display the score
    font = pygame.font.Font(font_name, size)
    text_surface = font.render(text, True, WHITE)       ## True denotes the font to be anti-aliased 
    text_rect = text_surface.get_rect()
    text_rect.midtop = (x, y)
    surf.blit(text_surface, text_rect)


def draw_shield_bar(surf, x, y, pct):
    if pct < 0:
        pct = 0 
    BAR_LENGTH = 100
    BAR_HEIGHT = 10
    fill = (pct / 100) * BAR_LENGTH
    outline_rect = pygame.Rect(x, y, BAR_LENGTH, BAR_HEIGHT)
    fill_rect = pygame.Rect(x, y, fill, BAR_HEIGHT)
    pygame.draw.rect(surf, GREEN, fill_rect)
    pygame.draw.rect(surf, WHITE, outline_rect, 2)


def draw_lives(surf, x, y, lives, img):
    for i in range(lives):
        img_rect= img.get_rect()
        img_rect.x = x + 30 * i
        img_rect.y = y
        surf.blit(img, img_rect)



def newmob():
    mob_element = Mob()
    all_sprites.add(mob_element)
    mobs.add(mob_element)

class Explosion(pygame.sprite.Sprite):
    def __init__(self, center, size):
        pygame.sprite.Sprite.__init__(self)
        self.size = size
        self.image = explosion_anim[self.size][0]
        self.rect = self.image.get_rect()
        self.rect.center = center
        self.frame = 0 
        self.last_update = pygame.time.get_ticks()
        self.frame_rate = 75

    def update(self):
        now = pygame.time.get_ticks()
        if now - self.last_update > self.frame_rate:
            self.last_update = now
            self.frame += 1
            if self.frame == len(explosion_anim[self.size]):
                self.kill()
            else:
                center = self.rect.center
                self.image = explosion_anim[self.size][self.frame]
                self.rect = self.image.get_rect()
                self.rect.center = center


class Player(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        ## scale the player img down
        self.image = pygame.transform.scale(player_img, (50, 38))
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        self.radius = 20
        self.rect.centerx = WIDTH / 2
        self.rect.bottom = HEIGHT - 10
        self.speedx = 0 
        self.shield = 100
        self.shoot_delay = 250
        self.last_shot = pygame.time.get_ticks()
        self.lives = 3
        self.hidden = False
        self.hide_timer = pygame.time.get_ticks()
        self.power = 1
        self.power_timer = pygame.time.get_ticks()

    def update(self):
        ## time out for powerups
        if self.power >=2 and pygame.time.get_ticks() - self.power_time > POWERUP_TIME:
            self.power -= 1
            self.power_time = pygame.time.get_ticks()

        ## unhide 
        if self.hidden and pygame.time.get_ticks() - self.hide_timer > 1000:
            self.hidden = False
            self.rect.centerx = WIDTH / 2
            self.rect.bottom = HEIGHT - 30

        self.speedx = 0     ## makes the player static in the screen by default. 
        # then we have to check whether there is an event hanlding being done for the arrow keys being 
        ## pressed 

        ## will give back a list of the keys which happen to be pressed down at that moment
        keystate = pygame.key.get_pressed()     
        if keystate[pygame.K_LEFT]:
            self.speedx = -5
        elif keystate[pygame.K_RIGHT]:
            self.speedx = 5

        #Fire weapons by holding spacebar
        if keystate[pygame.K_SPACE]:
            self.shoot()

        ## check for the borders at the left and right
        if self.rect.right > WIDTH:
            self.rect.right = WIDTH
        if self.rect.left < 0:
            self.rect.left = 0

        self.rect.x += self.speedx

    def shoot(self):
        ## to tell the bullet where to spawn
        now = pygame.time.get_ticks()
        if now - self.last_shot > self.shoot_delay:
            self.last_shot = now
            if self.power == 1:
                bullet = Bullet(self.rect.centerx, self.rect.top)
                all_sprites.add(bullet)
                bullets.add(bullet)
                shooting_sound.play()
            if self.power == 2:
                bullet1 = Bullet(self.rect.left, self.rect.centery)
                bullet2 = Bullet(self.rect.right, self.rect.centery)
                all_sprites.add(bullet1)
                all_sprites.add(bullet2)
                bullets.add(bullet1)
                bullets.add(bullet2)
                shooting_sound.play()

            """ MOAR POWAH """
            if self.power >= 3:
                bullet1 = Bullet(self.rect.left, self.rect.centery)
                bullet2 = Bullet(self.rect.right, self.rect.centery)
                missile1 = Missile(self.rect.centerx, self.rect.top) # Missile shoots from center of ship
                all_sprites.add(bullet1)
                all_sprites.add(bullet2)
                all_sprites.add(missile1)
                bullets.add(bullet1)
                bullets.add(bullet2)
                bullets.add(missile1)
                shooting_sound.play()
                missile_sound.play()

    def powerup(self):
        self.power += 1
        self.power_time = pygame.time.get_ticks()

    def hide(self):
        self.hidden = True
        self.hide_timer = pygame.time.get_ticks()
        self.rect.center = (WIDTH / 2, HEIGHT + 200)


# defines the enemies
class Mob(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image_orig = random.choice(meteor_images)
        self.image_orig.set_colorkey(BLACK)
        self.image = self.image_orig.copy()
        self.rect = self.image.get_rect()
        self.radius = int(self.rect.width *.90 / 2)
        self.rect.x = random.randrange(0, WIDTH - self.rect.width)
        self.rect.y = random.randrange(-150, -100)
        self.speedy = random.randrange(5, 20)        ## for randomizing the speed of the Mob

        ## randomize the movements a little more 
        self.speedx = random.randrange(-3, 3)

        ## adding rotation to the mob element
        self.rotation = 0
        self.rotation_speed = random.randrange(-8, 8)
        self.last_update = pygame.time.get_ticks()  ## time when the rotation has to happen

    def rotate(self):
        time_now = pygame.time.get_ticks()
        if time_now - self.last_update > 50: # in milliseconds
            self.last_update = time_now
            self.rotation = (self.rotation + self.rotation_speed) % 360 
            new_image = pygame.transform.rotate(self.image_orig, self.rotation)
            old_center = self.rect.center
            self.image = new_image
            self.rect = self.image.get_rect()
            self.rect.center = old_center

    def update(self):
        self.rotate()
        self.rect.x += self.speedx
        self.rect.y += self.speedy
        ## now what if the mob element goes out of the screen

        if (self.rect.top > HEIGHT + 10) or (self.rect.left < -25) or (self.rect.right > WIDTH + 20):
            self.rect.x = random.randrange(0, WIDTH - self.rect.width)
            self.rect.y = random.randrange(-100, -40)
            self.speedy = random.randrange(1, 8)        ## for randomizing the speed of the Mob

## defines the sprite for Powerups
class Pow(pygame.sprite.Sprite):
    def __init__(self, center):
        pygame.sprite.Sprite.__init__(self)
        self.type = random.choice(['shield', 'gun'])
        self.image = powerup_images[self.type]
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        ## place the bullet according to the current position of the player
        self.rect.center = center
        self.speedy = 2

    def update(self):
        """should spawn right in front of the player"""
        self.rect.y += self.speedy
        ## kill the sprite after it moves over the top border
        if self.rect.top > HEIGHT:
            self.kill()



## defines the sprite for bullets
class Bullet(pygame.sprite.Sprite):
    def __init__(self, x, y):
        pygame.sprite.Sprite.__init__(self)
        self.image = bullet_img
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        ## place the bullet according to the current position of the player
        self.rect.bottom = y 
        self.rect.centerx = x
        self.speedy = -10

    def update(self):
        """should spawn right in front of the player"""
        self.rect.y += self.speedy
        ## kill the sprite after it moves over the top border
        if self.rect.bottom < 0:
            self.kill()

        ## now we need a way to shoot
        ## lets bind it to "spacebar".
        ## adding an event for it in Game loop

## FIRE ZE MISSILES
class Missile(pygame.sprite.Sprite):
    def __init__(self, x, y):
        pygame.sprite.Sprite.__init__(self)
        self.image = missile_img
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        self.rect.bottom = y
        self.rect.centerx = x
        self.speedy = -10

    def update(self):
        """should spawn right in front of the player"""
        self.rect.y += self.speedy
        if self.rect.bottom < 0:
            self.kill()


###################################################
## Load all game images

background = pygame.image.load(path.join(img_dir, 'starfield.png')).convert()
background_rect = background.get_rect()
## ^^ draw this rect first 

player_img = pygame.image.load(path.join(img_dir, 'playerShip1_orange.png')).convert()
player_mini_img = pygame.transform.scale(player_img, (25, 19))
player_mini_img.set_colorkey(BLACK)
bullet_img = pygame.image.load(path.join(img_dir, 'laserRed16.png')).convert()
missile_img = pygame.image.load(path.join(img_dir, 'missile.png')).convert_alpha()
# meteor_img = pygame.image.load(path.join(img_dir, 'meteorBrown_med1.png')).convert()
meteor_images = []
meteor_list = [
    'meteorBrown_big1.png',
    'meteorBrown_big2.png', 
    'meteorBrown_med1.png', 
    'meteorBrown_med3.png',
    'meteorBrown_small1.png',
    'meteorBrown_small2.png',
    'meteorBrown_tiny1.png'
]

for image in meteor_list:
    meteor_images.append(pygame.image.load(path.join(img_dir, image)).convert())

## meteor explosion
explosion_anim = {}
explosion_anim['lg'] = []
explosion_anim['sm'] = []
explosion_anim['player'] = []
for i in range(9):
    filename = 'regularExplosion0{}.png'.format(i)
    img = pygame.image.load(path.join(img_dir, filename)).convert()
    img.set_colorkey(BLACK)
    ## resize the explosion
    img_lg = pygame.transform.scale(img, (75, 75))
    explosion_anim['lg'].append(img_lg)
    img_sm = pygame.transform.scale(img, (32, 32))
    explosion_anim['sm'].append(img_sm)

    ## player explosion
    filename = 'sonicExplosion0{}.png'.format(i)
    img = pygame.image.load(path.join(img_dir, filename)).convert()
    img.set_colorkey(BLACK)
    explosion_anim['player'].append(img)

## load power ups
powerup_images = {}
powerup_images['shield'] = pygame.image.load(path.join(img_dir, 'shield_gold.png')).convert()
powerup_images['gun'] = pygame.image.load(path.join(img_dir, 'bolt_gold.png')).convert()


###################################################


###################################################
### Load all game sounds
shooting_sound = pygame.mixer.Sound(path.join(sound_folder, 'pew.wav'))
missile_sound = pygame.mixer.Sound(path.join(sound_folder, 'rocket.ogg'))
expl_sounds = []
for sound in ['expl3.wav', 'expl6.wav']:
    expl_sounds.append(pygame.mixer.Sound(path.join(sound_folder, sound)))
## main background music
#pygame.mixer.music.load(path.join(sound_folder, 'tgfcoder-FrozenJam-SeamlessLoop.ogg'))
pygame.mixer.music.set_volume(0.2)      ## simmered the sound down a little

player_die_sound = pygame.mixer.Sound(path.join(sound_folder, 'rumble1.ogg'))
###################################################

## group all the sprites together for ease of update
all_sprites = pygame.sprite.Group()
player = Player()
all_sprites.add(player)

## spawn a group of mob
mobs = pygame.sprite.Group()
for i in range(8):      ## 8 mobs
    # mob_element = Mob()
    # all_sprites.add(mob_element)
    # mobs.add(mob_element)
    newmob()

## group for bullets
bullets = pygame.sprite.Group()
powerups = pygame.sprite.Group()

#### Score board variable
score = 0

## TODO: make the game music loop over again and again. play(loops=-1) is not working
# Error : 
# TypeError: play() takes no keyword arguments
#pygame.mixer.music.play()

#############################
## Game loop
running = True
menu_display = True
while running:
    if menu_display:
        main_menu()
        pygame.time.wait(3000)

        #Stop menu music
        pygame.mixer.music.stop()
        #Play the gameplay music
        pygame.mixer.music.load(path.join(sound_folder, 'tgfcoder-FrozenJam-SeamlessLoop.ogg'))
        pygame.mixer.music.play(-1)     ## makes the gameplay sound in an endless loop

        menu_display = False

    #1 Process input/events
    clock.tick(FPS)     ## will make the loop run at the same speed all the time
    for event in pygame.event.get():        # gets all the events which have occured till now and keeps tab of them.
        ## listening for the the X button at the top
        if event.type == pygame.QUIT:
            running = False

        ## Press ESC to exit game
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_ESCAPE:
                running = False
        # ## event for shooting the bullets
        # elif event.type == pygame.KEYDOWN:
        #     if event.key == pygame.K_SPACE:
        #         player.shoot()      ## we have to define the shoot()  function

    #2 Update
    all_sprites.update()


    ## check if a bullet hit a mob
    ## now we have a group of bullets and a group of mob
    hits = pygame.sprite.groupcollide(mobs, bullets, True, True)
    ## now as we delete the mob element when we hit one with a bullet, we need to respawn them again
    ## as there will be no mob_elements left out 
    for hit in hits:
        score += 50 - hit.radius         ## give different scores for hitting big and small metoers
        random.choice(expl_sounds).play()
        # m = Mob()
        # all_sprites.add(m)
        # mobs.add(m)
        expl = Explosion(hit.rect.center, 'lg')
        all_sprites.add(expl)
        if random.random() > 0.9:
            pow = Pow(hit.rect.center)
            all_sprites.add(pow)
            powerups.add(pow)
        newmob()        ## spawn a new mob

    ## ^^ the above loop will create the amount of mob objects which were killed spawn again
    #########################

    ## check if the player collides with the mob
    hits = pygame.sprite.spritecollide(player, mobs, True, pygame.sprite.collide_circle)        ## gives back a list, True makes the mob element disappear
    for hit in hits:
        player.shield -= hit.radius * 2
        expl = Explosion(hit.rect.center, 'sm')
        all_sprites.add(expl)
        newmob()
        if player.shield <= 0: 
            player_die_sound.play()
            death_explosion = Explosion(player.rect.center, 'player')
            all_sprites.add(death_explosion)
            # running = False     ## GAME OVER 3:D
            player.hide()
            player.lives -= 1
            player.shield = 100

    ## if the player hit a power up
    hits = pygame.sprite.spritecollide(player, powerups, True)
    for hit in hits:
        if hit.type == 'shield':
            player.shield += random.randrange(10, 30)
            if player.shield >= 100:
                player.shield = 100
        if hit.type == 'gun':
            player.powerup()

    ## if player died and the explosion has finished, end game
    if player.lives == 0 and not death_explosion.alive():
        running = False
        # menu_display = True
        # pygame.display.update()

    #3 Draw/render
    screen.fill(BLACK)
    ## draw the stargaze.png image
    screen.blit(background, background_rect)

    all_sprites.draw(screen)
    draw_text(screen, str(score), 18, WIDTH / 2, 10)     ## 10px down from the screen
    draw_shield_bar(screen, 5, 5, player.shield)

    # Draw lives
    draw_lives(screen, WIDTH - 100, 5, player.lives, player_mini_img)

    ## Done after drawing everything to the screen
    pygame.display.flip()       

pygame.quit()

Answer 1

You're following good style conventions, that's a good sign. A lot of people don't do this consistently. (Note I'm not sure if you're a beginner, you said this was your first game but that was all). You do occasionally let lines run too long or have the wrong spacing. It's best if you read the PEP0008, Python's official style guide. I have some general notes from reading through your code, but I've definitely missed things to be improved. On pep8online you can post your whole code in and get a breakdown of every part of your code that it finds in violation of PEP rules. It's not perfect, but will reveal some good rules for you to follow with tons of examples. I still recommend reading PEP0008 when you can.

You lay out colour constants at the start, but then you don't always use them. For instance, in main_menu, why use

screen.fill((0,0,0))

and not

screen.fill(BLACK)

At the risk of stating the obvious, constants are better to use as they're more readable to understand, and easier to change. If you decide that you want to adjust your colour palette to make the game look blue tinted, you could do that easily if all colours are set by your constant values.

In draw_shield_bar you use an if statement to ensure that pct is always 0 at the lowest. An alternative is to use max, which will return the maximum of values passed to it. ie. if you pass max(pct, 0) then it returns pct if it's 0 or higher, but otherwise will return 0. Your mileage may vary on which is more readable but I prefer:

pct = max(pct, 0)

I presume pct is percent, but it's not a clear name. Try to avoid such shortened names, they usually just add confusion. A clear full word makes your code a lot more readable, and shaving those characters doesn't really get you much.

Also you declare BAR_HEIGHT and BAR_LENGTH locally in the function but they're named as if they're constants, with all uppercase letters. You should either make them constants at the top level, alongside your other constants like the colours that will eventually be in constants.py or just declare them as normal values that happen to always be the same. ie. length = 100. I suggest the former, as long as you can name them clearly.

In draw_lives, you calculate img_rect.x by using 30. But since 30 isn't a variable, it's not at all clear what it corresponds to. This is known as a magic number, because the reason behind it is unknown to the reader. These should be avoided, instead you should have a named constant like LIFE_SPACING or something more appropriate so that it's much easier to follow what's happening.

Still on constants, you may like to use something called a Class constant. When you declare a class, you usually set its attributes in __init__, but you can also set constant attributes above __init__, in the class definition. Like this:

class Explosion(pygame.sprite.Sprite):

    FRAME_RATE = 75

    def __init__(self, center, size):
        ...

This makes it easier to see that FRAME_RATE is constant across all Explosions. It can still be accessed with self.Explosion, and can be additionally accessed with Explosion.FRAME_RATE, which can be useful when you want to get the value from outside a class instance context.