网络爬虫实践小结

背景

近期工作中要解决两个问题，一个是数据组需要网爬一些图片数据，另外一个是要批量爬取公司用于文档协同的一个网站上的附件。于是乎，就写了两个脚本去完成任务。

爬虫思路

第一步：向确定的url发送请求，接收服务器的响应信息；如果是需要用户登录的网页，需要手动获取cookie信息放入header中，或者模拟登录自动获取cookie。

第二步：对接收到的信息进行解析，找到需要的标签内容（通常是我们需要的图片或文件的url）；

第三步：向目标url发送请求，保存数据到本地。

python在网络爬虫方面提供了一些框架，Scrapy、Pyspider等，由于我们要实现的都是小功能，用一些现成的库即可。

爬取附件

1、发送简单请求用urllib.request.urlopen（url）就可以了，但如果要加入headers则可用urllib.request.Request类构造一个request实例，再调用urlopen发送请求。如要用到cookie：

（如果要实现模拟登录自动获取cookie，可参考爬虫实战学习笔记_2 网络请求urllib模块+设置请求头+Cookie+模拟登陆-CSDN博客）

import urllib.request
 
headers = {
             "Cookie": 'confluence.list.pages.cookie=list-content-tree;.......'
          }
 
req = urllib.request.Request(url, headers=headers)
response = urllib.request.urlopen(req)

2、解析响应体，这里是要找到附件链接的图标，在html中是的标签元素。用到BeautifulSoup。

from bs4 import BeautifulSoup
 
html = response.read().decode("utf8")
soup = BeautifulSoup(html, "lxml")
a_list = soup.find_all("a")
for a in a_list:
    if "class" in a.attrs:
        if "filename" in a["class"]:
            filename = a.text.strip()
            download_url = a['href']
            print(download_url)           

import requests
 
file = requests.get(download_url, headers=headers)
save_path = './download/'
if not os.path.exists(save_path):
    os.mkdir(save_path)
save_file = open(os.path.join(save_path, filename), 'wb')
save_file.write(file.content)
save_file.close()
print('save ok')

爬取图片

网上关于百度、google爬取关键字图片的开源代码很多，我也是找了一个开源代码进行稍微修改，目前满足实际需要。这里附上代码，供参考。

# -*- coding: UTF-8 -*-"""
import requests
import tqdm
import os
import json
 
def configs(search, page, number):
    url = 'https://image.baidu.com/search/acjson'
    params = {
        "tn": "resultjson_com",
        "logid": "11555092689241190059",
        "ipn": "rj",
        "ct": "201326592",
        "is": "",
        "fp": "result",
        "queryWord": search,
        "cl": "2",
        "lm": "-1",
        "ie": "utf-8",
        "oe": "utf-8",
        "adpicid": "",
        "st": "-1",
        "z": "",
        "ic": "0",
        "hd": "",
        "latest": "",
        "copyright": "",
        "word": search,
        "s": "",
        "se": "",
        "tab": "",
        "width": "",
        "height": "",
        "face": "0",
        "istype": "2",
        "qc": "",
        "nc": "1",
        "fr": "",
        "expermode": "",
        "force": "",
        "pn": str(60 * page),
        "rn": number,
        "gsm": "1e",
        "1617626956685": ""
    }
    return url, params
 
 
def loadpic(number, page, path):
    while (True):
        if number == 0:
            break
        url, params = configs(search, page, number)
        try:
            response = requests.get(url, headers=header, params=params).content.decode('utf-8')
            result = json.loads(response)
            url_list = []
            for data in result['data'][:-1]:
                url_list.append(data['thumbURL'])
            for i in range(len(url_list)):
                getImg(url_list[i], 60 * page + i, path)
                bar.update(1)
                number -= 1
                if number == 0:
                    break
            page += 1
        except Exception as e:
            print(e)
            continue
    print("\nfinish!")
 
 
def getImg(url, idx, result_path):
    img = requests.get(url, headers=header)
    file = open(result_path + str(idx + 1) + '.jpg', 'wb')
    file.write(img.content)
    file.close()
 
 
if __name__ == '__main__':
    search = "溜冰" # 爬取的关键词
    number = 100    #爬取的目标数量
    result_path = os.path.join(os.getcwd(), search)
    if not os.path.exists(result_path):
        os.mkdir(result_path)
    header = {
        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36'}
 
    bar = tqdm.tqdm(total=number)
    page = 0
    loadpic(number, page, result_path)