wait方法接会返回一个tuple(元组)，tuple中包含两个set(集合)，一个是completed(已完成的)另外一个是uncompleted(未完成的)。使用wait方法的一个优势就是获得更大的自由度，它接收三个参数FIRST_COMPLETED, FIRST_EXCEPTION 和ALL_COMPLETE，默认设置为ALL_COMPLETED。
我们通过下面这个例子来看一下三个参数的区别
from concurrent.futures import ThreadPoolExecutor, wait, as_completedfrom time import sleepfrom random import randintdef return_after_random_secs(num): sleep(randint(1, 5)) return "Return of {}".format(num)pool = ThreadPoolExecutor(5)futures = []for x in range(5): futures.append(pool.submit(return_after_random_secs, x))print(wait(futures))# print(wait(futures, timeout=None, return_when='FIRST_COMPLETED'))如果采用默认的ALL_COMPLETED，程序会阻塞直到线程池里面的所有任务都完成。
ziwenxie :: ~ » python example5.pyDoneAndNotDoneFutures(done={<Future at 0x7f0b06c9bc88 state=finished returned str>,<Future at 0x7f0b06cbaa90 state=finished returned str>,<Future at 0x7f0b06373898 state=finished returned str>,<Future