python从子线程中获得返回值

# coding:utf-8import timefrom threading import Threaddef foo(number):    time.sleep(20)    return numberclass MyThread(Thread):    def __init__(self, number):        Thread.__init__(self)        self.number = number    def run(self):        self.result = foo(self.number)    def get_result(self):        return self.resultthd1 = MyThread(3)thd2 = MyThread(5)thd1.start()thd2.start()thd1.join()thd2.join()print thd1.get_result()print thd2.get_result()