请问怎么取得多线程程序子进程的返回值?

CODE:

import threading

def show(sec):
        return sec

loops=[2,4]
threads = []

for i in range(len(loops)):
        t= threading.Thread(target=show,args=(loops[i],))
        threads.append(t)

for i in range(len(loops)):
        threads[i].start()

for i in range(len(loops)):
        threads[i].join()