scrapy爬虫系列之七--scrapy_redis的使用

功能点：如何发送携带cookie访问登录后的页面，如何发送post请求登录

简单介绍：

• 安装：pip3 install scrapy_redis
• 在scrapy的基础上实现了更多的功能：如request去重（增量爬虫），爬虫持久化，实现分布式
• 工作流程：通过redis实现调度器的队列和指纹集合；每个request生成一个指纹，在存入redis之前，首先判断这个指纹是否已经存在，如果不存在则存入。
• 配置：

  • # 确保所有的爬虫通过Redis去重
    DUPEFILTER_CLASS = 'scrapy_redis.dupefilter.RFPDupeFilter'
    # 启用Redis调度存储请求队列
    SCHEDULER = 'scrapy_redis.scheduler.Scheduler'
    # 不清除Redis队列、这样可以暂停/恢复 爬取
    SCHEDULER_PERSIST = True
    # 保存item到redis
    ITEM_PIPELINES = {
    'scrapy_redis.pipelines.RedisPipeline': 400
    }
    # reids服务器地址
    REDIS_URL = 'redis://192.168.3.20:6379'

• redis中访问:

  • keys *里有3个键
    爬虫名:requests Scheduler队列，存放待请求的request对象，获取的过程是pop操作，即获取一个会去除一个
    爬虫名:dupefilter 指纹集合，存放的是已经进入scheduler队列的request对象的指纹，指纹默认由请求方法、url和请求体组成
    爬虫名:items 存放的是获取到的item信息，在 pipeline中 开启才会存入。

• request对象什么时候入队？

  • 1、dont_filter=True，构造请求的时候，把dont_filter设置为True，该url会被反复抓取（url地址对应的内容会更新的情况，类似百度贴吧）
    2、一个全新的url地址被抓到的时候，构造request请求
    3、url地址在start_urls中的时候，会入队，不管之前是否请求过（原因：构造start_url地址的请求的时候，dont_filter=True）
    4、代码，scheduler.py的enqueue_request方法：

    def enqueue_request(self, request):
        if not request.dont_filter and self.df.request_seen(request):
            self.df.log(request, self.spider)
            return False
        self.queue.push(request)
        return True

• scrapy_redis的去重方法

  • 使用sha1加密request得到指纹
    把指纹存到redis的集合中
    下次新来的request，同样的方式生成指纹，判断指纹是否存在redis的集合中

• 生成指纹

  • fp = hashlib.sha1()
    fp.update(to_bytes(request.method))
    fp.update(to_bytes(canonicalize_url(request.url)))
    fp.update(request.body or b'')
    return fp.hexdigest()

• 判断数据是否存在redis的集合中，不存在则插入

  • dupefilter.py的request_seen方法
    added = self.server.sadd(self.key, fp)
    return added == 0

• 在引入scrapy_redis之前，scrapy是怎么去重的？　　

  • scrapy.dupefilters.py的 RFPDupeFilter，request_seen方法：
    # 首先也会生成一个指纹，判断是否在集合中，如果存在，说明已经抓取过
    # requests.seen文件
    def request_seen(self, request):
            fp = self.request_fingerprint(request)
            if fp in self.fingerprints:
                return True
            self.fingerprints.add(fp)
            if self.file:
                self.file.write(fp + os.linesep)

爬取网站：dmoz

完整代码：https://files.cnblogs.com/files/bookwed/dmoztools.zip

主要代码：

dmoz.py

# -*- coding: utf-8 -*-
import scrapy
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule

class DmozSpider(CrawlSpider):
    name = 'dmoz'
    allowed_domains = ['dmoztools.net']
    start_urls = ['http://www.dmoztools.net']

    rules = (
        Rule(LinkExtractor(
            restrict_css=('.top-cat', '.sub-cat', 'cat-item')
        ), callback='parse_item', follow=True),
    )

    def parse_item(self, response):
        for div in response.css(".title-and-desc"):
            yield {
                'name': div.css(".site-title::text").extract_first(),
                'desc': div.css(".site-descr::text").extract_first().strip(),
                'link': div.css("a::attr(href)").extract_first(),
            }

settings.py

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

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

BOT_NAME = 'dmoztools'

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

# 确保所有的爬虫通过Redis去重
DUPEFILTER_CLASS = 'scrapy_redis.dupefilter.RFPDupeFilter'
# 启用Redis调度存储请求队列
SCHEDULER = 'scrapy_redis.scheduler.Scheduler'
# 不清除Redis队列、这样可以暂停/恢复 爬取；队列中的内容是否持久化
SCHEDULER_PERSIST = True
# 使用优先级调度请求队列 （默认使用）
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.PriorityQueue'
# 可选用的其它队列
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.FifoQueue'
# SCHEDULER_QUEUE_CLASS = 'scrapy_redis.queue.LifoQueue'
# 最大空闲时间防止分布式爬虫因为等待而关闭
# SCHEDULER_IDLE_BEFORE_CLOSE = 10

# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'dmoztools (+http://www.yourdomain.com)'

# Obey robots.txt rules
ROBOTSTXT_OBEY = True

# 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://doc.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://doc.scrapy.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
#    'dmoztools.middlewares.DmoztoolsSpiderMiddleware': 543,
#}

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

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

# Configure item pipelines
# See https://doc.scrapy.org/en/latest/topics/item-pipeline.html
ITEM_PIPELINES = {
   'dmoztools.pipelines.DmoztoolsPipeline': 300,
   'scrapy_redis.pipelines.RedisPipeline': 400
}

# Enable and configure the AutoThrottle extension (disabled by default)
# See https://doc.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://doc.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'

REDIS_URL = 'redis://192.168.3.20:6379'