import pygame as pg
from pygame.locals import *

BLACK = (0,0,0)
WHITE = (255,255,255)
YELLOW = (255,255,0)
BLUE = (0,0,255)

SCREEN_SIZE = (500,500)

class Dirty(pg.sprite.Sprite):

    def __init__(self, color, rect, *groups):
        pg.sprite.Sprite.__init__(self, groups)

        self.color = color
        self.rect = rect

        self.image = pg.Surface((rect.width, rect.height))
        self.image.fill(color)

    def change_color(self,color):
        self.color = color
        self.image.fill(color)

    def render(self, screen):
        screen.blit(self.image, self.rect)


pg.init()
screen = pg.display.set_mode(SCREEN_SIZE)
clock = pg.time.Clock()

background = pg.Surface(SCREEN_SIZE)
background.fill(WHITE)

dirty_a = Dirty(YELLOW, pg.Rect(100,250,32, 32))
dirty_b = Dirty(BLUE, pg.Rect(400,250,32,32))

rect_a = pg.Rect(100,250,64,64)
rect_b = pg.Rect(400,250,64,64)

update_rect = None

while True:

    for event in pg.event.get():
        if event.type == pg.QUIT: exit()

        if event.type == pg.KEYDOWN:
            if event.key == pg.K_LEFT:
                background.fill(BLACK)
            if event.key == pg.K_RIGHT:
                background.fill(WHITE)
            if event.key == pg.K_UP:
                update_rect = rect_a
            if event.key == pg.K_DOWN:
                update_rect = rect_b




    screen.blit(background,(0,0))

    dirty_a.render(screen)
    dirty_b.render(screen)

    pg.display.update(update_rect)