Why my program doesn't work after launch?

I want to add endless clouds, but my program doesn’t work, what’s wrong?

class Cloud(pygame.sprite.Sprite):
    def __init__(self):
        super(Cloud, self).__init__()
        self.image = clouds_jpg
        self.image.set_colorkey(WHITE1)
        self.rect = self.image.get_rect()
        self.rect.centerx = random.randint(0, WIDTH)
        self.rect.centery = random.randint(HEIGHT - 550, HEIGHT)


    def update(self):
        self.rect.move_ip(-2, 0)
        if self.rect.right <= 0:
            self.rect.left = screen.get_width() 

all_sprites = pygame.sprite.Group()
player = Player()
cloud = Cloud()
all_sprites.add(player, cloud)
...
elif event.type == ADDCLOUD:
            new_cloud = Cloud()
            cloud.add(new_cloud)
            all_sprites.add(new_cloud)

Error:

Traceback (most recent call last): File "C:\Users\дом\My
project\111.py", line 117, in
cloud.add(new_cloud) File "C:\Users\дом\AppData\Local\Programs\Python\Python36\lib\site-packages\pygame\sprite.py",
line 133, in add
self.add(*group) TypeError: add() argument after * must be an iterable, not Cloud

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>Solution :

cloud is a pygame.sprite.Sprite. You only can add a pygame.sprite.Sprite object toto a pygame.sprite_Group:

clouds = pygame.sprite.Group()

elif event.type == ADDCLOUD:
    new_cloud = Cloud()
    
    # cloud.add(new_cloud)
    clouds.add(new_cloud)

    all_sprites.add(new_cloud)