Question

I’m writing a simple toy in Pygame. When you press a key on the home row, it does a little burst of particles.

class Particle():
    x = 0
    y = 0
    size = 0
    colour = (255, 255, 255)
    rect = None
    def __init__(self, x, y, size, colour):
        self.x = x
        self.y = y
        self.size = size
        self.colour = colour # Particle has its own colour 
        self.rect = pygame.Rect(self.x, self.y, self.size, self.size)

class Burst():
    x = 0
    y = 0
    colour = (255, 255, 255)
    count = 0
    sound = None
    particles = []

    def __init__(self, x, y, colour, count, sound):
        self.x = x
        self.y = y
        self.colour = colour # Burst has its own colour, too - all its particles should have the same colour as it
        self.count = count
        self.sound = sound
        self.particles.append(Particle(self.x, self.y, 5, self.colour))

    def update(self):
        self.particles.append(Particle(random.randint(1, 30) + self.x, random.randint(1, 30) + self.y, 5, self.colour))
    def draw(self):
        global screen
        for p in self.particles:
            pygame.draw.rect(screen, p.colour, p.rect) # This draws the particles with the correct colours
            #pygame.draw.rect(screen, self.colour, (60, 60, 120, 120), 4) # This draws the particles all the same colour
            #screen.fill(p.colour, p.rect) # This draws the particles all the same colour

The line you’re looking for is in Burst.draw. For some reason, only the uncommented one works correctly. The other two lines, which should be the same as far as I can tell, only draw the first burst’s particles correctly. Any subsequent bursts change all particles onscreen to match their colour.

I can provide more code, but there’s not much more to it. Basically keypresses add Bursts to an array, and every tick I step through that array calling update() and draw().

Does anyone know what I did wrong, and then accidentally fixed?

Answer 1

Because all particles in the screen belong to the same collection Burst.particles.
And every time you process a Burst you are processing all the particles, and all gets painted with the last colour.

Just move the initialization particles = [] to the init method.

def __init__(self, x, y, colour, count, sound):
    ...
    self.particles = []
    self.particles.append(Particle(self.x, self.y, 5, self.colour))

Update

You are using a Java/C# style of coding classes. You shouldn’t put any of the initializations at the class level, unless they are constants or class attributes.

IE:

class Burst():

    class_attribute = 0       # declaration of class (static) attribute

    def __init__(self, ...):
        self.attribute = 0    # declaration of object (regular) attribute

You shouldn’t make class declarations of attribute you will use a object attributes.
Just remove all the declarations previous to the init method in both classes.