最近在逛知乎时，看到这么一个问题

最高赞的答案写了个爬虫，把所有的照片都爬下来了。

嘿嘿嘿，技术的力量

正好自己也在学习，加上答主的答案是很久之前的，知乎已经改版了，所以决定自己用Python3写一个练习一下（绝对不是为了下照片）....

设个小小的目标：爬取所有“女性”程序员的照片。

首先是要知道“总的回答数”，这个比较简单：

url="https://www.zhihu.com/question/37787176"
html=requests.get(url,headers=headers).text
answer=BeautifulSoup(html,"lxml").find("h4",class_="List-headerText").find("span").get_text()
answer_num=int(re.sub("\s\S+","",answer))

知乎加载内容是通过点击“更多”，然后加载出20个回答，利用selenium模拟登陆太慢太麻烦，所有查看知乎的Ajax请求比较靠谱，此处感谢崔大神的教学（http://cuiqingcai.com/4380.html）。

通过浏览器，可以看到每次点击更多，请求内容是一个“fetch”类型的文件和相关的图片（jpeg），这个"fetch"文件包含了回答者信息和回答内容

通过json处理后，通过gender判断回答者性别（0为女，1为男）。

抓取“content”下的所有src属性的图片链接，就搞定了。

附注：请求头要加一个"authorization"

下面是全代码：

import requests
import os
import json
from bs4 import BeautifulSoup
import re
import time

headers = {
    ‘User-Agent‘: ‘Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36‘,
    "Connection": "keep - alive",
    "Accept": "text/html,application/xhtml+xml,application/xml;",
    "authorization": "Bearer Mi4wQUFEQVB4VkNBQUFBVU1MWktySDJDeGNBQUFCaEFsVk5TZ0YyV1FBaGsxRnJlTFd3ZGR6QzZrTXptcDFuWGNOQk5B|1498313802|2d5466ef4550588f5fc28553ea8981e7a4e398ad"
    }
isExists = os.path.exists("D:/crawler_study/zhihu")
if not isExists:
    os.makedirs("D:/crawler_study/zhihu")
    os.chdir("D:/crawler_study/zhihu")
else:
    os.chdir("D:/crawler_study/zhihu")

url="https://www.zhihu.com/question/37787176"
html=requests.get(url,headers=headers).text
answer=BeautifulSoup(html,"lxml").find("h4",class_="List-headerText").find("span").get_text()
answer_num=int(re.sub("\s\S+","",answer))
url_prefix="https://www.zhihu.com/api/v4/questions/37787176/answers?sort_by=default&include=data%5B%2A%5D.is_normal%2Cis_collapsed%2Ccollapse_reason%2Cis_sticky%2Ccollapsed_by%2Csuggest_edit%2Ccomment_count%2Ccan_comment%2Ccontent%2Ceditable_content%2Cvoteup_count%2Creshipment_settings%2Ccomment_permission%2Cmark_infos%2Ccreated_time%2Cupdated_time%2Creview_info%2Crelationship.is_authorized%2Cis_author%2Cvoting%2Cis_thanked%2Cis_nothelp%2Cupvoted_followees%3Bdata%5B%2A%5D.author.follower_count%2Cbadge%5B%3F%28type%3Dbest_answerer%29%5D.topics&limit=20&offset="
offset=0

while offset < answer_num:
    answer_url=url_prefix+str(offset)
    html=requests.get(answer_url,headers=headers).text
    content=json.loads(html)["data"]
    for row in content:
        gender=row["author"]["gender"]
        if gender == 0:
            answer=row["content"]
            pic_list=BeautifulSoup(answer,‘lxml‘).find_all("img")
            for pic in pic_list:
                down_url=pic["src"]
                if down_url.startswith("http"):
                    name=re.sub(".*/","",down_url)
                    file=open(name,"ab")
                    print("开始下载：",name)
                    file.write(requests.get(down_url).content)
                    print("下载完：", name)
                    file.close()
        else:
            pass
    offset+=20
    time.sleep(3)

爬取知乎某个问题下所有的图片