思路分析：
requests 获得需要爬取的网页
将爬取的网页数据做成BeautifulSoup
应用soup 的API 找到需要的标签属性
通过标签属性获得二进制字节保存
import requests
from bs4 import BeautifulSoup
data = requests.get("url")
data.encoding = data.apparent_encoding
soup = BeautifulSoup(data.text)
link = soup.select_one("#container > div > div > div:nth-child(3) > div.list_con_box > div.zt_con_img > dl > dd > ul > li:nth-child(1) > a > img")['src']
f = open("D://a.jpg","wb")
pic_data = requests.get(link)
f.write(pic_data.content)
f.close()
