Scrapy突破反爬虫的限制

爬虫和反爬的对抗过程以及策略

爬虫和反爬虫基本概念

  • 爬虫:自动获取网站数据的程序,关键是批量的获取。
  • 反爬虫:使用技术手段防止爬虫程序的方法。
  • 误伤:反爬虫技术将普通用户识别为爬虫,如果误伤过高,效果再高也不能用。
  • 成本:反爬虫需要的人力和机器成本。
  • 拦截:成功拦截爬虫,一般拦截率越高,误伤率越高。

反爬虫的目的

  • 初级爬虫—-简单粗暴,不管服务器压力,容易弄挂网站。
  • 数据保护
  • 失控的爬虫—-由于某些情况下,忘记或者无法关闭的爬虫。
  • 商业竞争对手

爬虫和反爬虫的过程

scrapy架构源码分析

scrapy架构

通过downloadmiddleware随机更换user-agent

方式一:headers设置随机更好user-agent

import random
random_index = random.randint(0,len(user_agent_list)-1)
random_agent = user_agent_list[random_index]
headers = {
    "HOST": "www.zhihu.com",
    "Referer": "https://www.zhizhu.com",
    'User-Agent': random_agent
}

方式二:downloadmiddleware随机更换user-agent

该随机模块可以拿来直接用,需要安装包:fake_useragent

#middlewares.py
from fake_useragent import UserAgent ##这是一个随机UserAgent的包,里面有很多UserAgent

class RandomUserAgentMiddlware(object):
    #随机更换user-agent
    def __init__(self, crawler):
        super(RandomUserAgentMiddlware, self).__init__()
        self.ua = UserAgent()
        self.ua_type = crawler.settings.get("RANDOM_UA_TYPE", "random")

    @classmethod
    def from_crawler(cls, crawler):
        return cls(crawler)

    def process_request(self, request, spider):
        def get_ua():
            return getattr(self.ua, self.ua_type)

        request.headers.setdefault('User-Agent', get_ua())
        
#settings.py
DOWNLOADER_MIDDLEWARES = {
'scrapy.downloadermiddlewares.useragent.userAgentMiddleware':None,#这里要设置原来的scrapy的useragent为None,否者会被覆盖掉
'ArticleSpider.middlewares.RandomUserAgentMiddlware':542,
}
RANDOM_UA_TYPE='random'

scrapy实现ip代理池

`scrapy`实现ip代理池

爬取西刺的免费ip代理

import requests
from scrapy.selector import Selector
import MySQLdb

conn = MySQLdb.connect(host="127.0.0.1", user="root", passwd="meiyi8013", db="article_spider", charset="utf8")
cursor = conn.cursor()

def crawl_ips():
    #爬取西刺的免费ip代理
    headers = {"User-Agent":"Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0"}
    for i in range(1568):
        re = requests.get("http://www.xicidaili.com/nn/{0}".format(i), headers=headers)

        selector = Selector(text=re.text)
        all_trs = selector.css("#ip_list tr")


        ip_list = []
        for tr in all_trs[1:]:
            speed_str = tr.css(".bar::attr(title)").extract()[0]
            print(speed_str)
            if speed_str:
                speed = float(speed_str.split("秒")[0])
            all_texts = tr.css("td::text").extract()

            ip = all_texts[0]
            port = all_texts[1]
            proxy_type = all_texts[5]

            ip_list.append((ip, port, proxy_type, speed))

        for ip_info in ip_list:
            cursor.execute(
                "insert proxy_ip(ip, port, speed, proxy_type) VALUES('{0}', '{1}', {2}, 'HTTP')".format(
                    ip_info[0], ip_info[1], ip_info[3]
                )
            )

            conn.commit()


class GetIP(object):
    def delete_ip(self, ip):
        #从数据库中删除无效的ip
        delete_sql = """
            delete from proxy_ip where ip='{0}'
        """.format(ip)
        cursor.execute(delete_sql)
        conn.commit()
        return True

    def judge_ip(self, ip, port):
        #判断ip是否可用
        http_url = "http://www.baidu.com"
        proxy_url = "http://{0}:{1}".format(ip, port)
        try:
            proxy_dict = {
                "http":proxy_url,
            }
            response = requests.get(http_url, proxies=proxy_dict)
        except Exception as e:
            print ("invalid ip and port")
            self.delete_ip(ip)
            return False
        else:
            code = response.status_code
            if code >= 200 and code < 300:
                print ("effective ip")
                return True
            else:
                print  ("invalid ip and port")
                self.delete_ip(ip)
                return False


    def get_random_ip(self):
        #从数据库中随机获取一个可用的ip
        random_sql = """
            SELECT ip, port FROM proxy_ip
            ORDER BY RAND()
            LIMIT 1
            """
        result = cursor.execute(random_sql)
        for ip_info in cursor.fetchall():
            ip = ip_info[0]
            port = ip_info[1]

            judge_re = self.judge_ip(ip, port)
            if judge_re:
                return "http://{0}:{1}".format(ip, port)
            else:
                return self.get_random_ip()



# print (crawl_ips())
if __name__ == "__main__":
    crawl_ips()
    # get_ip = GetIP()
    # get_ip.get_random_ip()

sql语言取出随机记录:在此是随机取出一条记录是ip和端口组成代理IP

SELECT ip, port FROM proxy_ip
ORDER BY RAND()
LIMIT 1

可以使用scrapy中的selector,代码如下:

from scrapy.selector import Selector
html=requests.get(url)
Selector=Selector(text=html.text)
Selector.xpath()

动态设置ip代理模版以后直接拿来用即可:

#middlewares.py
from tools.crawl_xici_ip import GetIP

class RandomProxyMiddleware(object):
    #动态设置ip代理
    def process_request(self, request, spider):
        get_ip = GetIP()
        request.meta["proxy"] = get_ip.get_random_ip()

#settings.py
DOWNLOADER_MIDDLEWARES = {
'ArticleSpider.middlewares.RandomProxyMiddleware':541,
}

云打码实现验证码识别

  • 编码实现(tesseract-ocr)
  • 在线打码—-打码平台(云打码、若快)
  • 人工打码

cookie禁用、自动限速、自定义spidersettings

如果用不到cookies的,就不要让对方知道你的cookies(如不需要登录的网站)。

#settings.py
COOKIES_ENABLED = False

custom_settings :对框架中的内容进行覆盖,比如我想覆盖setting中的headers的内容,那么只要将header的内容写入custom_settings中,然后改变headers的值即可, 当程序再次运行时会覆盖以前settingheaders值,而运行你修改之后的内容。

自定义spidersettings

class ZhihuSpider(scrapy.Spider):
    custom_settings = {
        'DEFAULT_REQUEST_HEADERS' : {
        'User-Agent': None,
        'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
        'Accept-Language': 'en',
    }

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