pygame para loop para forma de desenho

import pygame 
from pygame.locals import *
from sys import exit
from random import *

pygame.init()

screen = pygame.display.set_mode((640, 480), 0,32)

class Rectangle:
    def __init__(self, pos, color, size):
        self.pos = pos
        self.color = color
        self.size = size
    def draw(self):
        pygame.draw.rect(screen, self.color, Rect(self.pos, self.size))

rectangles = []     

for count in range(10):
    random_color = (randint(0,255), randint(0,255), randint(0,255))
    random_pos = (randint(0,639), randint(0,479))
    random_size = (639-randint(random_pos[0], 639), 479-randint(random_pos[1],479))

    rectangles.append(Rectangle(random_pos, random_color, random_size))



while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            exit()
    screen.lock()
    for rectangle in rectangles:
        rectangle.draw()
    screen.unlock()
    pygame.display.update()
Determined Dugong