增量式 爬虫

# 增量式 爬虫

概念: 监测网站的数据更新的情况,只爬取网站更新的数据.

核心: 去重

实现 Redis  set集合也行

--  如何实现redis去重? --

# 爬取电影站的更新数据   url去重  https://www.4567tv.tv/frim/index1.html# 下面代码以 http://www.922dyy.com/dianying/dongzuopian/ 为例 作为起始页

# spider.py 爬虫文件
# -*- coding: utf-8 -*-
import scrapy
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule
from redis import Redis
from shipin.items import ShipinItem
class DianyingSpider(CrawlSpider):
    conn = Redis(host=‘127.0.0.1‘,port=6379) # 连接对象
    name = ‘dianying‘
    # allowed_domains = [‘www.xx.com‘]
    start_urls = [‘http://www.922dyy.com/dianying/dongzuopian/‘]

    rules = (
        Rule(LinkExtractor(allow=r‘/dongzuopian/index\d+\.html‘), callback=‘parse_item‘, follow=False), #这里需要所有页面时候改为True
    )  # 只提取页码url

    def parse_item(self, response):
        # 解析出当前页码对应页面中 电影详情页 的url
        li_list = response.xpath(‘/html/body/div[2]/div[2]/div[2]/ul/li‘)
        for li in li_list:
            # 解析详情页的url
            detail_url = ‘http://www.922dyy.com‘ + li.xpath(‘./div/a/@href‘).extract_first()
            #
            ex = self.conn.sadd(‘mp4_detail_url‘,detail_url) # 有返回值
            # ex == 1 该url没有被请求过     ex==0在集合中,该url已经被请求过了
            if ex==1:
                print(‘有新数据可爬.....‘)
                yield scrapy.Request(url=detail_url,callback=self.parse_detail)
            else:
                print(‘暂无新数据可以爬取‘)

    def parse_detail(self,response):
        name = response.xpath(‘//*[@id="film_name"]/text()‘).extract_first()
        m_type = response.xpath(‘//*[@id="left_info"]/p[1]/text()‘).extract_first()
        print(name,‘--‘,m_type)
        item = ShipinItem() #实例化
        item[‘name‘] = name
        item[‘m_type‘] = m_type

        yield item

# items.py
# -*- coding: utf-8 -*-

import scrapy

class ShipinItem(scrapy.Item):

    name = scrapy.Field()
    m_type = scrapy.Field()

# pipelines.py 管道
# -*- coding: utf-8 -*-

class ShipinPipeline(object):
    def process_item(self, item, spider):
        conn = spider.conn
        dic = {
            ‘name‘:item[‘name‘],
            ‘m_type‘:item[‘m_type‘]
        }
        conn.lpush(‘movie_data‘,str(dic)) #一般这里不str的话会报错,数据类型dict的错误
        return item

# settings.py  里面

ITEM_PIPELINES = {
   ‘shipin.pipelines.ShipinPipeline‘: 300,
}

BOT_NAME = ‘shipin‘

SPIDER_MODULES = [‘shipin.spiders‘]
NEWSPIDER_MODULE = ‘shipin.spiders‘

USER_AGENT = ‘Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.86 Safari/537.36‘

ROBOTSTXT_OBEY = False

LOG_LEVEL = ‘ERROR‘

流程: scrapy startproject Name

　　  cd Name

　　  scrapy genspider -t crawl 爬虫文件名 www.example.com

注意点: 增量式爬虫,会判断url在不在集合里面,sadd (集合的方法) 返回值1就是没在里面,就是新数据.

　　　　lpush lrange llen  --key  都是redis里面列表类型的方法

下面是糗事百科段子页面的数据 (作者/段子)   增量式爬取

# 爬虫.py
# -*- coding: utf-8 -*-
import scrapy,hashlib
from qbPro.items import QbproItem
from redis import Redis

# 只爬取当前页面
class QiubaiSpider(scrapy.Spider):
    name = ‘qiubai‘

    conn = Redis(host=‘127.0.0.1‘,port=6379)
    start_urls = [‘https://www.qiushibaike.com/text/‘]

    def parse(self, response):
        div_list = response.xpath(‘//*[@id="content-left"]/div‘)
        for div in div_list:
            # 数据指纹:爬取到一条数据的唯一标识
            author = div.xpath(‘./div/a[2]/h2/text() | ./div/span[2]/h2/text()‘).extract_first().strip()
            content = div.xpath(‘./a/div/span[1]//text()‘).extract()
            content = ‘‘.join(content).replace(‘\n‘,‘‘)
            item = QbproItem()  # 实例化
            item[‘author‘] = author
            item[‘content‘] = content

            # 给爬取到的数据生成一个数据指纹
            data = author+content
            hash_key = hashlib.sha256(data.encode()).hexdigest()
            ex = self.conn.sadd(‘hash_key‘,hash_key)  # 输指纹存进 集合里面
            if ex == 1:
                print(‘有数据更新‘)
                yield item
            else:
                print(‘无数据更新‘)

# items.py
# -*- coding: utf-8 -*-
import scrapy
class QbproItem(scrapy.Item):

    author = scrapy.Field()
    content = scrapy.Field()

# pipelines.py  管道
# -*- coding: utf-8 -*-
class QbproPipeline(object):
    def process_item(self, item, spider):
        conn = spider.conn
        dic = {
            ‘author‘: item[‘author‘],
            ‘content‘: item[‘content‘]
        }
        conn.lpush(‘qiubai‘, str(dic))
        return item

# settings.py  设置
ITEM_PIPELINES = {
   ‘qbPro.pipelines.QbproPipeline‘: 300,
}

USER_AGENT =  ‘Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.86 Safari/537.36‘
ROBOTSTXT_OBEY = False
LOG_LEVEL = ‘ERROR‘

原文地址：https://www.cnblogs.com/zhangchen-sx/p/10849234.html