Python variables change in every object

Question

I'm playing around with pygame for the first time, trying to make multiple rectangles move across the screen. Here's my code:

import pygame

pygame.init()

scrWidth = 1200
scrHeigth = 900
done = False
rectangles = []

screen = pygame.display.set_mode((scrWidth, scrHeigth))
clock = pygame.time.Clock()

class Rectangle:
    speed = [1,1]
    colourSpeed = 300
    colourID = 0
    colour = (0, 0, 255)
    size = 60

    def __init__(self, name = "", x=0, y=0, speed=False, colour=False, size=False):
        self.name = name
        self.x = x
        self.y = y
        self.doesSpeed = speed
        self.doesColour = colour
        self.doesSize = size

    def draw(self):
        pygame.draw.rect(screen, self.colour, pygame.Rect(self.x, self.y, self.size, self.size))

    def checkCollision(self):
        if self.x < 0 or self.x > scrWidth-self.size:
            self.speed[0] = -self.speed[0]
        if self.y < 0 or self.y > scrHeigth-self.size:
            self.speed[1] = -self.speed[1]

    def move(self):
        self.x += self.speed[0]
        self.y += self.speed[1]

    def changeColour(self):
        self.colourID = (self.colourID+1)%self.colourSpeed
        if 0 <= self.colourID < (self.colourSpeed/3):
            self.colour = (0, 0, 255)
        elif (self.colourSpeed/3) <= self.colourID < (2*self.colourSpeed/3):
            self.colour = (0, 255, 0)
        elif (2*self.colourSpeed/3) <= self.colourID < self.colourSpeed:
            self.colour = (255, 0, 0)




rect1 = Rectangle("rect1", 30, 30, False, True, False)
rectangles.append(rect1)
rect2 = Rectangle("rect2", 300, 300)
rectangles.append(rect2)


while not done:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done=True

    screen.fill((0, 0, 0))
    for obj in rectangles:
        obj.checkCollision()
        if obj.doesColour: obj.changeColour()
        obj.move()
        obj.draw()

    pygame.display.flip()
    clock.tick(60)

The problem is that when a rectangle collides with the edge of the screen all rectangles change direction(speed). However if I make rectangles with different speeds this doesn't happen.

ex: rect1 has speed [1,1] and rect2 has speed [2,2].

What's causing this and how can I fix it?

I don't know why you have a class variable for speed, but I would recommend you to get rid of it. You need to also adjust it in every method... — user5653854
– user5653854, Commented Dec 2, 2016 at 7:16
speed is a class attribute, mutable value shared across all instances. You have to create individual list in each instance __init__ method. — Łukasz Rogalski
– Łukasz Rogalski, Commented Dec 2, 2016 at 7:21

Marek Nowaczyk · Accepted Answer · 2016-12-02 08:38:20Z

1

Move the speed, colourSpeed, colourID, colour, size to the init method.

At that moment that fields are defined as class fields, so they are changed globally for all rectangles.

Solution:

def __init__(self, name = "", x=0, y=0, speed=False, colour=False, size=False):
        self.name = name
        self.x = x
        self.y = y
        self.doesSpeed = speed
        self.doesColour = colour
        self.doesSize = size
        # here it comes
        self.speed = [1,1]
        self.colourSpeed = 300
        self.colourID = 0
        self.colour = (0, 0, 255)
        self.size = 60

edited Dec 2, 2016 at 8:38

answered Dec 2, 2016 at 7:17

Marek Nowaczyk

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4 Comments

SJ_WTF Over a year ago

thanks, that worked. How come it did work when I changed the speed to an absolute value? (rect1.speed = [2,2])

user5653854 Over a year ago

@SJ_WTF I would like to see your code now, because with this solution really nothing changes

SJ_WTF Over a year ago

@LPK yeah answered before the code block showed up in this answer for me. You should have self.speed etc inside the init

Marek Nowaczyk Over a year ago

Sorry, I just copied lines straight to initializator. Now it should work.

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