How to make sprites in a group update their position independently using class method update()?

Question

Hi I'm new to using pygame and I'm trying to build a game with sprites of puppies moving randomly around the screen and bouncing off the boundaries.

I'm using the method update() within my sprite class on my group of sprites ' puppies ' to update the sprites' individual locations, however when I run the code all of the sprites seem to move together so I'm wondering if I should be structuring the code differently or putting the sprites in individual groups?

Here's the code:

import pygame, random

pygame.init()

class puppy(pygame.sprite.Sprite):
    def __init__(self, pos_x, pos_y,filepath, speed=[2,2]):
        super().__init__()
        self.image = pygame.image.load(filepath)
        self.rect=self.image.get_rect()
        self.rect.center = [pos_x,pos_y]
        self.speed = speed
    def update(self):
        if (self.rect.x < 0) or (self.rect.x > 850):
            self.speed[0] *= -1
        if (self.rect.y < 0) or (self.rect.y > 615):
            self.speed[1] *= -1
        self.rect.x = self.rect.x + self.speed[0]
        self.rect.y = self.rect.y + self.speed[1]

puppies = pygame.sprite.Group()

dogimages = ['pupp1.png','pupp2.png','pupp3.png','pupp4.png','pup5.png']


for i in range(5):
    new_pup=puppy(random.randint(75,925),random.randint(75,675),dogimages[i])
    puppies.add(new_pup)

screen = pygame.display.set_mode((1000, 750))
screen.fill((255,255,255))
clock=pygame.time.Clock()
background = pygame.image.load('bg.jpeg')

running=True
while running:
    clock.tick(60)
    pygame.display.update()
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    screen.blit(background, (0, 0))
    puppies.draw(screen)
    puppies.update()
    pygame.display.update()

score 1 · Answer 1 · answered Jul 06 '23 at 08:19

You are using a list [2,2] as a default value. Using mutables as default values is highly discouraged as it can lead to all sorts of issues: see here for a discussion on why this is the case.

It would be better to do:

class puppy(pygame.sprite.Sprite):
    def __init__(self,pos_x, pos_y, filepath, speed=None):
        if speed is None:
            speed = [2, 2]
        ...

which is how mutable default arguments are usually implemented to avoid this exact issue.

How to make sprites in a group update their position independently using class method update()?

1 Answers1