Pygame Snake Eating Itself

Question

I've recently started using pygame and I'm following TheNewBostons's youtube tutorial. Here's my main game loop:

def game_loop():
    global direction
    global tdirection

    lead_x=display_width/2
    lead_y=display_height/2

    block_size=10
    change_x=10
    change_y=0

    game_exit=False
    GameOver=False
    main_menu=False


    snakelist=[]
    snakelength=1

    applethickness=20

    RandAppleX=round(random.randrange(0, display_width-applethickness )/10.0)*10.0
    RandAppleY=round(random.randrange(0, display_height-applethickness )/10.0)*10.0



    while not game_exit:


        while GameOver==True:
            game_display.fill(white)
            message_screen('You lost, Press Q to quit or C to retry.', red)
            pygame.display.update()
            for event in pygame.event.get():
                if event.type==pygame.KEYDOWN:
                    if event.key==pygame.K_q:
                        loss.play()
                        game_exit=True
                        GameOver= False


                    elif event.key==pygame.K_c:
                        direction='right'
                        game_loop()


                if event.type==pygame.QUIT:
                    game_exit=True
                    GameOver= False




        for event in pygame.event.get():


            if event.type==pygame.QUIT:
                game_exit=True

            if event.type==pygame.KEYDOWN:
                if event.key==pygame.K_a:

                    change_x=-block_size
                    direction='left'

                    change_x=-block_size                        
                    change_y=0
                elif event.key==pygame.K_d:
                    direction='right'

                    change_x=block_size
                    change_y=0  
                elif event.key==pygame.K_w:
                    direction='up'

                    change_y=-block_size
                    change_x=0
                elif event.key==pygame.K_s:
                    direction='down'

                    change_y=block_size
                    change_x=0

                elif event.key==pygame.K_ESCAPE:
                    pause()





        if lead_x>=display_width or lead_x<0 or lead_y>=display_height or lead_y<0:
            loss.play()
            GameOver=True



        lead_x+=change_x
        lead_y+=change_y




        clock.tick(FPS)





        snakehead=[]

        snakehead.append(lead_x)
        snakehead.append(lead_y)

        snakelist.append(snakehead)


        if len(snakelist)>snakelength:
            del snakelist[0]

        for segment in snakelist[:-1]:
            if segment==snakehead:
                loss.play()
                GameOver=True






        game_display.fill(white)
        game_display.blit(aimg, (RandAppleX, RandAppleY))   

        snake(snakelist, block_size)
        score(snakelength-1)




        if lead_x>= RandAppleX and lead_x<= RandAppleX+applethickness and lead_y<= RandAppleY+applethickness and lead_y>= RandAppleY:


            RandAppleX=round(random.randrange(0, display_width-applethickness )/10.0)*10.0
            RandAppleY=round(random.randrange(0, display_height-applethickness )/10.0)*10.0
            snakelength+=1
            effect.play()





        pygame.display.update()




    pygame.quit()
    quit()

Now I need to prevent the snake from eating itself when its moving in a certain direction. For example then its moving to the right, pressing the A button on my keyboard would instantly make it eat itself and if its moving up pressing the S button would do the same thing. Is there a way to prevent this from happening?

Answer 1

While changing the direction, you can just check if the direction is the opposite to the current direction and, if that's the case, not set the new direction. This fixes the problem.

Answer 2

An easy solution could be to prevent the snake from backing into itself by checking that the direction it is moving in is not opposite the requested direction. This would involve a few extra checks. Something like this:

        if event.type==pygame.KEYDOWN:
            if event.key==pygame.K_a and direction != 'right':

                change_x=-block_size
                direction='left'

                change_x=-block_size                        
                change_y=0
            elif event.key==pygame.K_d and direction != 'left':
                direction='right'

                change_x=block_size
                change_y=0  
            elif event.key==pygame.K_w and direction != 'down':
                direction='up'

                change_y=-block_size
                change_x=0
            elif event.key==pygame.K_s and direction != 'right':
                direction='down'

                change_y=block_size
                change_x=0