python---多线程下载图片

import requests
import threading
import hashlib
import time


def down_pic(url):
    print("开始下载",url)
    r = requests.get(url)
    file_name = hashlib.md5(url.encode()).hexdigest() + '.jpg'
    with open(file_name, 'wb') as fw:
        fw.write(r.content)
    print("%s下载结束"%url)

urls = ['http://sky.nnzhp.cn/static/avatar/default.jpg',
        'http://sky.nnzhp.cn/static/avatar/labi.jpg',
        'http://sky.nnzhp.cn/static/avatar/login.jpg',
        'http://sky.nnzhp.cn/static/avatar/%E7%8B%97%E5%A4%B42.jpg',
        'http://sky.nnzhp.cn/static/avatar/wsj.jpg',
        'http://sky.nnzhp.cn/static/avatar/demo1.png'
        ]

#单线程
# start_time = time.time()
# for url in urls:
#     down_pic(url)
# print("下载用时",time.time() - start_time)

#多线程
start_time = time.time()
for url in urls:
    t = threading.Thread(target=down_pic,args=[url])
    t.start()

while threading.activeCount()!=1:
    pass

print("下载用时",time.time() - start_time)