无法弄清楚如何在我的pygame中成倍增加外星人？

Question

So I've just been writing a dodger game for practice using pygame and python. I've read a lot of tutorials and looked at other similar games to help me. Basically, aliens come down from the top of the screen (they're supposed to be random sizes and speeds and their location is supposed to be random as well) and the player uses their mouse to move the spaceship to dodge the falling aliens.

I have an if statement that is supposed to multiply the aliens coming down from the top but when I run the game only one alien falls and when it reaches the end of the screen it just disappears. No other aliens appear. The program is still running so the game hasn't ended.

Here is my full code.

import pygame
import random
import sys
from pygame.locals import *
alienimg = pygame.image.load('C:\\Python27\\alien.png')
playerimg = pygame.image.load('C:\\Python27\\spaceship.png')

def playerCollision(playerRect, aliens): # a function for when the player hits an alien
    for a in aliens:
        if playerRect.colliderect(a['rect']):
            return True
    return False

def screenText(text, font, screen, x, y): #text display function
    textobj = font.render(text, 1, (255, 255, 255))
    textrect = textobj.get_rect()
    textrect.topleft = (x,y)
    screen.blit(textobj, textrect)

def main(): #this is the main function that starts the game

    pygame.init()

    screen = pygame.display.set_mode((500,500))
    clock = pygame.time.Clock()
    pygame.mouse.set_visible(False)
    pygame.display.set_caption('Dodge the Aliens') 
    font = pygame.font.SysFont("monospace", 45)


    pressed = pygame.key.get_pressed()

    aliens = []
    score = 0
    alienAdd = 0
    addedaliens = 0
    gameOver = False
    moveLeft = moveRight = moveUp = moveDown = False
    topScore = 0
    while gameOver==False: #while loop that actually runs the game
        score += 1

        playerImage =   pygame.image.load('C:\\Python27\\spaceship.png').convert() # the player images
        playerRect = playerImage.get_rect()
        screen.blit(playerImage, [300, 250])
        alienImage = pygame.image.load('C:\\Python27\\alien.png').convert() #alien images
        alienRect = alienImage.get_rect()
        screen.blit(alienImage, [ 50, 50 ])
        pygame.display.flip()


        for event in pygame.event.get(): #key controls
            if event.type == KEYDOWN and event.key == pygame.K_ESCAPE: #escape ends the game
                gameOver = True
            elif event.type == MOUSEMOTION:
                playerRect.move_ip(event.pos[0] - playerRect.centerx, event.pos[1] - playerRect.centery)
        screen.fill((0,0,0))
        pygame.display.flip()


        if not gameOver:
            alienAdd += 1
        if alienAdd == 6: # randomly adding aliens of different sizes and speeds
            aliendAdd = 0
            alienSize = random.randint(8, 25)
            newAlien = {'rect': pygame.Rect(random.randint(0, 500 - alienSize), 0 -alienSize, alienSize, alienSize),
                    'speed': random.randint(1, 8),
                    'surface':pygame.transform.scale(alienImage, (alienSize, alienSize)),
                    }
            aliens.append(newAlien)

        if moveLeft and playerRect.left > 0:
            playerRect.move_ip(-1 * 5, 0)
        if moveRight and playerRect.right < 500:
            playerRect.move_ip(5, 0)
        if moveUp and playerRect.top > 0:
            playerRect.move_ip(0, -1 * 5)
        if moveDown and playerRect.bottom < 500:
            playerRect.move_ip(0, 5)

        for a in aliens:
            if not gameOver:
                a['rect'].move_ip(0, a['speed'])


        for a in aliens[:]:
            if a['rect'].top > 500:
                aliens.remove(a) #removes the aliens when they get to the bottom of the screen

        screenText('Score %s' % (score), font, screen, 10, 0)
        screen.blit(playerImage, playerRect)

        pygame.display.update()

        for a in aliens:
            screen.blit(a['surface'], a['rect'])
        pygame.display.flip()


        if playerCollision(playerRect, aliens):
            if score > topScore:
                topScore = score
            gameOver = True


        clock.tick(30)

    screenText('Game Over!', font, screen, (750 / 6), ( 750 / 6))
    screenText('Press ENTER To Play Again.', font, screen, ( 750 / 6) - 80, (750 / 6) + 50)
    pygame.display.update()

if __name__ == "__main__":
    main()

Also, sidenote, whenever I put my code in here I go down every line and indent it. Is there an easier way to do that?

Answer 1

You have a typo in aliendAdd = 0 , it should be alienAdd = 0 . This is causing you to keep incrementing alienAdd more and more and not hit your if statement of alienAdd == 6 again.