python多线程的执行分析

from random import randint
from threading import Thread
from time import time, sleep
 
class DownloadTask(Thread):
    def __init__(self, filename):
        super().__init__()
        self._filename = filename
 
    def run(self):
        print('开始下载%s...'% self._filename)
        time_to_download = randint(5,10)
        sleep(time_to_download)
        print('%s下载完成!耗费了%d秒' %(self._filename, time_to_download))
 
def main():
    start = time()
    t1 = DownloadTask('python入门')
    t2 = DownloadTask('av.avi')
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    end = time()
    print('共耗费了%.2f秒'%(end - start))
 
if __name__ == '__main__':
    main()