增量式爬虫

增量式爬虫

• 概念:检测网站数据跟新的状况,爬取更新数据

• 核心:去重!!!

• 增量式爬虫

  • 深度爬取类型的网站中须要对详情页的url进行记录和检测

    • 记录:将爬取过的详情页的url进行记录保存

      • url存储到redis的set中
      • redis的sadd方法存取时,若是数据存在返回值为0,若是不存在返回值为1;

    • 检测：若是对某一个详情页的url发起请求以前先要取记录表中进行查看，该url是否存在，存在的话觉得
      着这个url已经被爬取过了。

    • 代码示例

      spider.py文件

    import scrapy
    from scrapy.linkextractors import LinkExtractor
    from scrapy.spiders import CrawlSpider, Rule
    from redis import Redis
    from zjs_moviePro.items import ZjsMovieproItem
    class MovieSpider(CrawlSpider):
        name = 'movie'
        conn = Redis(host='127.0.0.1',port=6379)
        # allowed_domains = ['www.xxx.com']
        start_urls = ['https://www.4567tv.tv/index.php/vod/show/id/6.html']
    
        rules = (#/index.php/vod/show/id/6/page/2.html
            Rule(LinkExtractor(allow=r'id/6/page/\d+\.html'), callback='parse_item', follow=False),
        )
    
        def parse_item(self, response):
            li_list = response.xpath('/html/body/div[1]/div/div/div/div[2]/ul/li')
            for li in li_list:
                name = li.xpath('./div/div/h4/a/text()').extract_first()
                detail_url = 'https://www.4567tv.tv'+li.xpath('./div/div/h4/a/@href').extract_first()
                ex = self.conn.sadd('movie_detail_urls',detail_url)
                if ex == 1:#向redis的set中成功插入了detail_url
                    print('有最新数据可爬......')
                    item = ZjsMovieproItem()
                    item['name'] = name
                    yield scrapy.Request(url=detail_url,callback=self.parse_detail,meta={'item':item})
                else:
                    print('该数据已经被爬取过了！')
        def parse_detail(self,response):
            item = response.meta['item']
            desc = response.xpath('/html/body/div[1]/div/div/div/div[2]/p[5]/span[2]/text()').extract_first()
            item['desc'] = desc
    
            yield item

    • item中建立属性

      import scrapy
      class ZjsMovieproItem(scrapy.Item):
          # define the fields for your item here like:
          name = scrapy.Field()
          desc = scrapy.Field()

    • 管道文件中

      class ZjsMovieproPipeline(object):
          def process_item(self, item, spider):
              conn = spider.conn
              conn.lpush('movie_data',item)
              return item