pygame2-2

#!/usr/bin/env python
#-*- coding:utf-8 -*-
import pygame
import sys

size = alto,ancho = 400,400
xy = [0,5]
color = [119,255,221]

def cargar_imagen(nombre,alfa=False):
    imagen = pygame.image.load(nombre)
    if alfa == True:
        imagen = imagen.convert_alpha()
    else:
        imagen = imagen.convert()
    return imagen

class Pelota(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.imagen = cargar_imagen("objeto.png",alfa=True)
        self.rect = self.imagen.get_rect()
        self.rect.centerx = 30
        self.rect.centery = 30
    def update(self):
        if self.rect.colliderect(rect1.rect):
            self.rect.centery = rect1.rect.centery - 15
        if self.rect.colliderect(rect2.rect):
            self.rect.centery = rect2.rect.centery - 15
        if self.rect.centerx <= 10:
            self.rect.centerx = 10
        if self.rect.centery >= alto - 10:
            self.rect.centery = alto - 10
        if self.rect.centerx >= ancho - 10:
            self.rect.centerx = ancho - 10

class Rect(pygame.sprite.Sprite):
    def __init__(self,x,y):
        self.x = x
        self.y = y
        pygame.sprite.Sprite.__init__(self)
        self.imagen = cargar_imagen("rectangulo.png",alfa=True)
        self.rect = self.imagen.get_rect()
        self.rect.centerx = self.x
        self.rect.centery = self.y

screen = pygame.display.set_mode(size)
pygame.display.set_caption("Ejemplo 2")
pelota = Pelota()
imagen_pelota = pelota.imagen
rect1 = Rect(75,90)
rect2 = Rect(150,140)
imagen_rect1 = rect1.imagen
imagen_rect2 = rect2.imagen
jugando = True
clock = pygame.time.Clock()
pygame.key.set_repeat(1,15)

while jugando:
    clock.tick(50)
    for eventos in pygame.event.get():
        if eventos.type == pygame.QUIT:
            jugando = False
        elif eventos.type == pygame.KEYDOWN:
            if eventos.key == pygame.K_q or eventos.key == pygame.K_ESCAPE:
                jugando = False
            elif eventos.key == pygame.K_LEFT:
                pelota.rect.centerx -= 5
            elif eventos.key == pygame.K_RIGHT:
                pelota.rect.centerx += 5
    pelota.rect = pelota.rect.move(xy)
    pelota.update()
    screen.fill(color)
    screen.blit(imagen_pelota, pelota.rect)
    screen.blit(imagen_rect1, rect1.rect)
    screen.blit(imagen_rect2, rect2.rect)
    pygame.display.flip()
else:
    sys.exit()