场景2的实现：

数据指纹

• 使用详情页的url充当数据指纹即可。

创建爬虫爬虫文件：

• cd project_name（进入项目目录）
• scrapy genspider 爬虫文件的名称（自定义一个名字即可） 起始url
  • （例如：scrapy genspider first www.xxx.com）
• 创建成功后，会在爬虫文件夹下生成一个py的爬虫文件

进入爬虫文件：

• cd 爬虫文件的名称（即自定义的名字）

爬虫文件

import scrapy
import redis
import random
from ..items import Zlsdemo2ProItem
class JianliSpider(scrapy.Spider):
    name = "jianli"
    # allowed_domains = ["www.xxx.com"]
    start_urls = ["https://sc.chinaz.com/jianli/free.html"]
        # 连接数据库
    conn = redis.Redis(
        host='127.0.0.1',
        port=6379,
    )
    def parse(self, response):
        div_list = response.xpath('//*[@id="container"]/div')
        for div in div_list:
            title = div.xpath('./p/a/text()').extract_first()
            detail_url = div.xpath('./p/a/@href').extract_first()
            # print(title, detail_url)
            ex = self.conn.sadd('data_id', detail_url)
            #建立item对象
            item = Zlsdemo2ProItem()
            item['title'] = title#将title传给item
            if ex == 1:#数据库中没有存储爬取到的数据
                print('有最新数据更新，正在采集中......')
                #做请求传参，将title通过meta传递给parse_detail函数
                yield scrapy.Request(url=detail_url,callback=self.parse_detail,meta={'item':item})

            else:#数据库中已存储爬取到的数据
                print('暂无数据更新！')

    def parse_detail(self,response):
        item = response.meta['item']
        download_li = response.xpath('//*[@id="down"]/div[2]/ul/li')
        download_urls = []
        for li in download_li:
            download_url_e = li.xpath('./a/@href').extract_first()
            download_urls.append(download_url_e)
        download_url = random.choice(download_urls)
        item['download_url'] = download_url

        yield item

items.py

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

import scrapy


class Zlsdemo2ProItem(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    title = scrapy.Field()
    download_url = scrapy.Field()
    

pipelines.py

# 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


# useful for handling different item types with a single interface
from itemadapter import ItemAdapter


class Zlsdemo2ProPipeline:
    def process_item(self, item, spider):

        conn = spider.conn
        conn.lpush('data1', item)

        return item

settings

# Scrapy settings for zlsDemo2Pro 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 = "zlsDemo2Pro"

SPIDER_MODULES = ["zlsDemo2Pro.spiders"]
NEWSPIDER_MODULE = "zlsDemo2Pro.spiders"


# Crawl responsibly by identifying yourself (and your website) on the user-agent
USER_AGENT : "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.163 Safari/537.36"
# Obey robots.txt rules
ROBOTSTXT_OBEY = False
LOG_LEVEL = 'ERROR'
LOG_LEVEL = 'WARNING'

# 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 = {
#    "zlsDemo2Pro.middlewares.Zlsdemo2ProSpiderMiddleware": 543,
#}

# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    "zlsDemo2Pro.middlewares.Zlsdemo2ProDownloaderMiddleware": 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 = {
   "zlsDemo2Pro.pipelines.Zlsdemo2ProPipeline": 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"

# Set settings whose default value is deprecated to a future-proof value
REQUEST_FINGERPRINTER_IMPLEMENTATION = "2.7"
TWISTED_REACTOR = "twisted.internet.asyncioreactor.AsyncioSelectorReactor"
FEED_EXPORT_ENCODING = "utf-8"