16-增量式爬虫

时间:2019-10-10
本文章向大家介绍16-增量式爬虫，主要包括16-增量式爬虫使用实例、应用技巧、基本知识点总结和需要注意事项，具有一定的参考价值，需要的朋友可以参考一下。

增量式爬虫

　　增量式爬虫，顾名思义。就是当网站更新新的内容的时候，能够将新内容储存下来，而不是将原来的数据又储存下来。例如电影网站每隔一段时间就更新新的电影，小说网站每天更新新的小说。

　　因此增量式爬虫就是发送请求之前，判断这个url是否爬取过，解析出数据判断是否爬取过：

　　　　　　　　　　1、对爬取过的url进行储存

　　　　　　　　　　2、对爬取过的数据进行储存（数据进行哈希储存（节约资源））

　　　　　　　　　　3、判断储存的数据是否已经存在

去重方法：

　　　　1）将爬取中的url进行储存，储存在redis的set中。下次爬取数据时，首先对即将要发送请求的url对储存在url的set中做判断，如果存在，就不发送请求，否则继续发送请求。

　　　　2）爬取到的内容进行唯一身份的标识，然后讲这个唯一标识储存在redis的set中。当下次爬取到网页数据的时候，在进行持久化存储之前，首先可以判断该数据的身份标识是否存在在redis的set中。如果存在，就不储存。如果不存在，就储存身份标识以及数据。

1、url去重

spiders/Movie.py

# -*- coding: utf-8 -*-
import scrapy
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule
#导入redis 储存数据
from redis import Redis
from Addcrawl.items import AddcrawlItem

class MovieSpider(CrawlSpider):
    name = 'Movie'
    #注销掉允许作用域
    # allowed_domains = ['www.xxx.com']
    start_urls = ['https://www.4567tv.tv/frim/index7.html']

    rules = (
        Rule(LinkExtractor(allow=r'/frim/index7-\d+\.html'), callback='parse_item', follow=True),

    )
    #创建redis对象，不能放在parse_item这样每调用方法就会被实例化，
    # 因此应该放在只被实例化一次的地方
    conn = Redis(host="127.0.0.1",port=6379)
    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:
            #获取详情页的url
            detail_url ="http://www.4567tv.tv"+(li.xpath('./div/a/@href').extract_first())
            #将详情页的url储存在redis的set中
            ret = self.conn.sadd("urls",detail_url)
            #经验证，此数据插入成功会返回1，否则返回0
            if ret == 1:
                print("这条url没有采集，可以进行采集！")
                yield scrapy.Request(url=detail_url,callback=self.parse_detail)
            else:
                print("已经爬取过，不能在爬取")
    def parse_detail(self,response):
        page = response.xpath('/html/body/div[1]/div/div/div/div[2]')
        item = AddcrawlItem()
        item["title"] = page.xpath('./h1/text()').extract_first()
        content = page.xpath('./p[5]/span[2]/text()').extract_first()
        item["content"] = "".join(content)
        yield item

items.py

# -*- coding: utf-8 -*-

# Define here the models for your scraped items
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/items.html

import scrapy


class AddcrawlItem(scrapy.Item):
    # define the fields for your item here like:
    title = scrapy.Field()
    content = scrapy.Field()

pipelines.py

# -*- coding: utf-8 -*-

# Define your item pipelines here
#
# Don't forget to add your pipeline to the ITEM_PIPELINES setting
# See: https://docs.scrapy.org/en/latest/topics/item-pipeline.html


class AddcrawlPipeline(object):
    def process_item(self, item, spider):
        dic = {
            "title":item["title"],
            "content":item["content"],
        }
        print(dic)
        #将数据储存入redis中
        spider.conn.lpush("moviedatas",dic)
        return item

settings.py

# -*- coding: utf-8 -*-

# Scrapy settings for Addcrawl project
#
# For simplicity, this file contains only settings considered important or
# commonly used. You can find more settings consulting the documentation:
#
#     https://docs.scrapy.org/en/latest/topics/settings.html
#     https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#     https://docs.scrapy.org/en/latest/topics/spider-middleware.html

BOT_NAME = 'Addcrawl'

SPIDER_MODULES = ['Addcrawl.spiders']
NEWSPIDER_MODULE = 'Addcrawl.spiders'


# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'Addcrawl (+http://www.yourdomain.com)'
USER_AGENT = 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36'
# Obey robots.txt rules
ROBOTSTXT_OBEY = False
LOG_LEVEL = "ERROR"
# Configure maximum concurrent requests performed by Scrapy (default: 16)
#CONCURRENT_REQUESTS = 32

# Configure a delay for requests for the same website (default: 0)
# See https://docs.scrapy.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs
#DOWNLOAD_DELAY = 3
# The download delay setting will honor only one of:
#CONCURRENT_REQUESTS_PER_DOMAIN = 16
#CONCURRENT_REQUESTS_PER_IP = 16

# Disable cookies (enabled by default)
#COOKIES_ENABLED = False

# Disable Telnet Console (enabled by default)
#TELNETCONSOLE_ENABLED = False

# Override the default request headers:
#DEFAULT_REQUEST_HEADERS = {
#   'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
#   'Accept-Language': 'en',
#}

# Enable or disable spider middlewares
# See https://docs.scrapy.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
#    'Addcrawl.middlewares.AddcrawlSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'Addcrawl.middlewares.AddcrawlDownloaderMiddleware': 543,
#}

# Enable or disable extensions
# See https://docs.scrapy.org/en/latest/topics/extensions.html
#EXTENSIONS = {
#    'scrapy.extensions.telnet.TelnetConsole': None,
#}

# Configure item pipelines
# See https://docs.scrapy.org/en/latest/topics/item-pipeline.html
ITEM_PIPELINES = {
   'Addcrawl.pipelines.AddcrawlPipeline': 300,
}

# Enable and configure the AutoThrottle extension (disabled by default)
# See https://docs.scrapy.org/en/latest/topics/autothrottle.html
#AUTOTHROTTLE_ENABLED = True
# The initial download delay
#AUTOTHROTTLE_START_DELAY = 5
# The maximum download delay to be set in case of high latencies
#AUTOTHROTTLE_MAX_DELAY = 60
# The average number of requests Scrapy should be sending in parallel to
# each remote server
#AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
# Enable showing throttling stats for every response received:
#AUTOTHROTTLE_DEBUG = False

# Enable and configure HTTP caching (disabled by default)
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
#HTTPCACHE_ENABLED = True
#HTTPCACHE_EXPIRATION_SECS = 0
#HTTPCACHE_DIR = 'httpcache'
#HTTPCACHE_IGNORE_HTTP_CODES = []
#HTTPCACHE_STORAGE = 'scrapy.extensions.httpcache.FilesystemCacheStorage'
settings.py

2、数据去重

# -*- coding: utf-8 -*-
import scrapy
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule
#导入redis 储存数据
from redis import Redis
from Addcrawl.items import AddcrawlItem
#导入哈希
import hashlib
class MovieSpider(CrawlSpider):
    name = 'Movie'
    #注销掉允许作用域
    # allowed_domains = ['www.xxx.com']
    start_urls = ['https://www.4567tv.tv/frim/index7.html']

    rules = (
        Rule(LinkExtractor(allow=r'/frim/index7-\d+\.html'), callback='parse_item', follow=True),

    )
    #创建redis对象，不能放在parse_item这样每调用方法就会被实例化，
    # 因此应该放在只被实例化一次的地方
    conn = Redis(host="127.0.0.1",port=6379)
    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:
            #获取详情页的url
            detail_url ="http://www.4567tv.tv"+(li.xpath('./div/a/@href').extract_first())
            yield scrapy.Request(url=detail_url,callback=self.parse_detail)

    def parse_detail(self,response):
        page = response.xpath('/html/body/div[1]/div/div/div/div[2]')
        item = AddcrawlItem()
        item["title"] = page.xpath('./h1/text()').extract_first()
        content = page.xpath('./p[5]/span[2]/text()').extract_first()
        item["content"] = "".join(content)
        #将解析到的数据生成唯一身份标识的进行redis储存
        source = item["title"]+item["content"]
        source_id = hashlib.sha256(source.encode()).hexdigest()
        #将解析内容的唯一标识储存到redis的data_id中
        ret = self.conn.sadd("data_id",source_id)
        if ret == 1:
            print("这条数据没有爬取过！！！")
            yield item
        else:
            print("已经爬取过啦！！！")
爬虫文件
# -*- coding: utf-8 -*-

# Define here the models for your scraped items
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/items.html

import scrapy


class AddcrawlItem(scrapy.Item):
    # define the fields for your item here like:
    title = scrapy.Field()
    content = scrapy.Field()
items.py
# -*- coding: utf-8 -*-

# Define your item pipelines here
#
# Don't forget to add your pipeline to the ITEM_PIPELINES setting
# See: https://docs.scrapy.org/en/latest/topics/item-pipeline.html


class AddcrawlPipeline(object):
    def process_item(self, item, spider):
        dic = {
            "title":item["title"],
            "content":item["content"],
        }
        print(dic)
        #将数据储存入redis中
        spider.conn.lpush("moviedatas2",dic)
        return item
pipelines.py
# -*- coding: utf-8 -*-

# Scrapy settings for Addcrawl project
#
# For simplicity, this file contains only settings considered important or
# commonly used. You can find more settings consulting the documentation:
#
#     https://docs.scrapy.org/en/latest/topics/settings.html
#     https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#     https://docs.scrapy.org/en/latest/topics/spider-middleware.html

BOT_NAME = 'Addcrawl'

SPIDER_MODULES = ['Addcrawl.spiders']
NEWSPIDER_MODULE = 'Addcrawl.spiders'


# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'Addcrawl (+http://www.yourdomain.com)'
USER_AGENT = 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36'
# Obey robots.txt rules
ROBOTSTXT_OBEY = False
LOG_LEVEL = "ERROR"
# Configure maximum concurrent requests performed by Scrapy (default: 16)
#CONCURRENT_REQUESTS = 32

# Configure a delay for requests for the same website (default: 0)
# See https://docs.scrapy.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs
#DOWNLOAD_DELAY = 3
# The download delay setting will honor only one of:
#CONCURRENT_REQUESTS_PER_DOMAIN = 16
#CONCURRENT_REQUESTS_PER_IP = 16

# Disable cookies (enabled by default)
#COOKIES_ENABLED = False

# Disable Telnet Console (enabled by default)
#TELNETCONSOLE_ENABLED = False

# Override the default request headers:
#DEFAULT_REQUEST_HEADERS = {
#   'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
#   'Accept-Language': 'en',
#}

# Enable or disable spider middlewares
# See https://docs.scrapy.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
#    'Addcrawl.middlewares.AddcrawlSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'Addcrawl.middlewares.AddcrawlDownloaderMiddleware': 543,
#}

# Enable or disable extensions
# See https://docs.scrapy.org/en/latest/topics/extensions.html
#EXTENSIONS = {
#    'scrapy.extensions.telnet.TelnetConsole': None,
#}

# Configure item pipelines
# See https://docs.scrapy.org/en/latest/topics/item-pipeline.html
ITEM_PIPELINES = {
   'Addcrawl.pipelines.AddcrawlPipeline': 300,
}

# Enable and configure the AutoThrottle extension (disabled by default)
# See https://docs.scrapy.org/en/latest/topics/autothrottle.html
#AUTOTHROTTLE_ENABLED = True
# The initial download delay
#AUTOTHROTTLE_START_DELAY = 5
# The maximum download delay to be set in case of high latencies
#AUTOTHROTTLE_MAX_DELAY = 60
# The average number of requests Scrapy should be sending in parallel to
# each remote server
#AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
# Enable showing throttling stats for every response received:
#AUTOTHROTTLE_DEBUG = False

# Enable and configure HTTP caching (disabled by default)
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
#HTTPCACHE_ENABLED = True
#HTTPCACHE_EXPIRATION_SECS = 0
#HTTPCACHE_DIR = 'httpcache'
#HTTPCACHE_IGNORE_HTTP_CODES = []
#HTTPCACHE_STORAGE = 'scrapy.extensions.httpcache.FilesystemCacheStorage'
settings.py
总结：增量式爬虫就是对数据去重，两种方法，一种对爬取过的url去重，另一种就是对储存过的数据去重。因此都是现将数据或者url单独储存起来，然后再将插入数据的返回值作为判断依据。来爬取最新的数据。
 

原文地址：https://www.cnblogs.com/lishuntao/p/11647602.html

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