python从子线程中获得返回值的方法

# coding:utf-8
import time
 
from threading import Thread
 
def foo(number):
  time.sleep(20)
  return number
 
class 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.result
 
 
thd1 = MyThread(3)
thd2 = MyThread(5)
thd1.start()
thd2.start()
thd1.join()
thd2.join()
 
print thd1.get_result()
print thd2.get_result()