threading join用法

join()：在子线程完成运行之前，这个子线程的父线程将一直被阻塞

import threading #线程
import time

def Beijing(n):
    print('Beijing time is start %s' % time.strftime('%Y-%m-%d %X', time.localtime()))
    time.sleep(2)
    print('Beijing time is over %s' % time.strftime('%Y-%m-%d %X', time.localtime()))

def Shanghai(n):
    print('Shanghai time is start %s' %time.strftime('%Y-%m-%d %X',time.localtime()))
    time.sleep(5)
    print('Shanghai time is over %s' %time.strftime('%Y-%m-%d %X',time.localtime()))

if __name__ == '__main__':
    t1 = threading.Thread(target=Beijing,args=(10,)) 
    t1.start()

    t2 = threading.Thread(target=Shanghai, args=(2,)) 
    t2.start()

    t1.join()   #join 等待,t1.jion  就是必须等t1运行完成后,在接着运行后面的代码
    print('Done')

运行的结果是:
　　Beijing time is start 2018-05-29 17:37:18
　　Shanghai time is start 2018-05-29 17:37:18
　　Beijing time is over 2018-05-29 17:37:20
　　Done
　　Shanghai time is over 2018-05-29 17:37:23

# Beijing Shanghai 同时执行开始时间 然后等待2秒,运行完beijing;接着打印Done;3秒后开始打印Shanghai结束时间