import requests
import os

root = 'C://Users//HP123//Desktop//new//z//'
url = "http://upload-images.jianshu.io/upload_images/3459828-fe024299e76685da.jpg?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240"
kv = {'user-agent':'Mozilla/5.0'}
path = root+url.split('/')[-1][1:5]+'.png'
try:
    if not os.path.exists(root):
        os.mkdir(root)
    if not os.path.exists(path):
        r = requests.get(url,headers = kv)
        r.raise_for_status()
        with open(path,'wb') as f:
            f.write(r.content)
            f.close()
            print('done')
    else:
        print('exited')
except:
    print("failed")

可能出现的问题：
爬是爬下来了，但是网上有些图片打不开，重新换张图片地址，尽量找那些他们放在文本的图片试试，百度出来的图片有些打不开……