I'm creating a little space shooter game. I need to limit the amount of times a player can fire, I'm setting a 2 second limit. But whenever I try to implement that it just won't work. The bullets keep firing multiple times a second.

Here's my code, I'd be very grateful if something could help:

def main():
    screen = pygame.display.set_mode((1000,750))
    pygame.display.set_caption("Alien Invasion")

    #load the bitmaps
    background = pygame.image.load("background.jpg").convert_alpha()
    space_ship = pygame.image.load("space_ship.tga").convert_alpha(background)

    #create the objects
    player = Space_Ship("space_ship.tga", screen)
    asteroid_small = Asteroid(screen, "small")
    asteroid_large = Asteroid(screen, "large")
    asteroid_medium = Asteroid(screen, "medium")

    #load the groups
    asteroid_group = pygame.sprite.Group()
    bullet_group = pygame.sprite.Group()
    asteroid_group.add(asteroid_small, asteroid_large, asteroid_medium)

    clock_start = 0

    #start the main game loop
    while True:
        clock_start = time.clock()
        for event in pygame.event.get():
            if event.type == QUIT:

        keys = pygame.key.get_pressed()
        if keys[K_SPACE]:
            if clock_start > 2:
                bullet = Space_Ship_Ammo(screen, player)
                clock_start = 0

        #draw the background
        screen.blit(background, (0,0))

        #update the sprites



Maybe I'm missing something, but how are you keeping time? You set clock_start, but I don't see the math to determine how much time has elapsed. I would expect something like

clock_start = time.clock()

time_elapsed = time.clock() - clock_start

if time_elapsed > 2:
    ....(and so on)

time.clock() gives different outputs when we look at its implementation in linux vs the implementation in windows. thereby we need to first determine which OS are you making the game for.

Stating that, line 25 and 26 of the above snippet seems to indicate that you re-assign clock_start everytime in the loop. This might cause unwanted circumstances happening for you.

Maybe a better solution would be that you note down the time a certain bullet was fired.. Keep iterating and check

if current_time - last_fired > 2 : 
    // do something 
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