How to keep a sprite drawn even after the the condition that drew it is no longer valid?

Question

The question I have has to do with a specific portion of my code in Pygame where I m trying to draw a new sprite onto the screen every couple of seconds.

  def spawn(self):
    self.count += 2
    alien1_sprite = Alien1((rand.randrange(38,462),50))
    rem = self.count % 33
    if rem == 0:
      self.alien1 = pygame.sprite.Group()
      self.alien1.add(alien1_sprite)
      self.alien1.draw(screen) 

Whenever I call the spawn function no sprites exist at the same time, how can I resolve this issue?

Answer 1

The problem is, you create a new Group for each alien. You only have to create the Group once and add the Alien Sprites to this one Group:

• Create the alien1 Group in the constructor (init) of the class.
• Add the aliens in spawn method.
• Draw all the aliens in the Group using your "draw" method. (The name of your method may be different - I don't know)

class ...

    def __init__(self):
        # [...]
 
        self.alien1 = pygame.sprite.Group() # creat the group in the constructor

    def spawn(self):
        self.count += 2
        rem = self.count % 33
        if rem == 0:
            alien1_sprite = Alien1((rand.randrange(38,462),50))
            self.alien1.add(alien1_sprite)
      
    def draw(self):    # your draw or render method

       # [...]

       self.alien1.draw(screen)  # draw all the aliens

Read the documentation of pygame.sprite.Group. The Group manages the Sprites it contains. The Group is the "list" that stores the Sprites.