scrapy基础二

应对反爬虫机制

①、禁止cookie ：有的网站会通过用户的cookie信息对用户进行识别和分析，此时可以通过禁用本地cookies信息让对方网站无法识别我们的会话信息

settings.py里开启禁用cookie

# Disable cookies (enabled by default)
COOKIES_ENABLED = False

②、设置下载延时：有的网站会对网页的访问频率进行分析，如果爬取过快，会被判断为自动爬取行为

settings.py里设置下载延时

#DOWNLOAD_DELAY = 3　　#去掉注释，3代表3秒

③、使用ip池： 有的网站会对用户的ip进行判断，所以需要多个ip地址。这些地址组成一个ip池，爬虫每次爬取会从ip池中随机选择一个ip,此时可以为爬虫项目建立一个中间件文件，定义ip使用规则

#1、创建项目略过
 
#2、settings.py 设置代理ip地址池
 
IPPOOL=[
    {"ipaddr":"proxyip1"},
    {"ipaddr":"proxyip2"},
    {"ipaddr":"proxyip3"},
    {"ipaddr":"proxyip4"},
    {"ipaddr":"proxyip5"},
    {"ipaddr":"proxyip6"},
    {"ipaddr":"proxyip7"}
]
 
#3、创建一个中间件文件 middle_download_wares.py
 
#-*-coding:utf-8-*-
 
import random
from mulitispd.settings import IPPOOL
from scrapy.contrib.downloadermiddleware.httpproxy import HttpProxyMiddleware
 
class IPPOOLS(HttpProxyMiddleware):
    def __init__(self,ip=''):
        self.ip = ip
 
    def process_request(self, request, spider):
        thisip = random.choice(IPPOOL)
        print ("current ip "+thisip["ipaddr"])
        request.meta['proxy'] = "http://"+thisip['ipaddr']
 
#4设置settings.py注册为项目中间件，格式：中间件所在目录.中间件文件名.中间件内部要使用的类
DOWNLOADER_MIDDLEWARES = {
   #'mulitispd.middlewares.MulitispdDownloaderMiddleware': 543,
    'scrapy.contrib.downloadermiddleware.httpproxy.HttpProxyMiddleware':123,
    'mulitispd.middle_download_wares.IPPOOLS':125
}

测试结果：

④、使用用户代理池： User-Agent变换使用，方法流程与使用ippool方法一样

#1、设置settings.py 里User-agent
 
UAPOOL=[
    "MOzilla/5.0 ...",
    "Chrom/49.0.2623.22 ....."
]
 
#2、新建中间件文件
 
#-*-coding:utf-8-*-
 
import random
from mulitispd.settings import UAPOOL
from scrapy.contrib.downloadermiddleware.useragent import UserAgentMiddleware
 
class UAPOOLS(UserAgentMiddleware):
    def __init__(self,useragent=''):
        self.useragent = useragent
 
    def process_request(self, request, spider):
        thisua = random.choice(UAPOOL)
        print ("current useragent "+thisua)
        request.headers.setdefault("User-Agent",thisua)
 
#3、settings.py注册中间件
DOWNLOADER_MIDDLEWARES = {
   #'mulitispd.middlewares.MulitispdDownloaderMiddleware': 543,
    'scrapy.contrib.downloadermiddleware.httpproxy.HttpProxyMiddleware':123,
    'mulitispd.middle_download_wares.IPPOOLS':125,
    'scrapy.contrib.downloadermiddleware.useragent.UserAgentMiddleware':2,
    'mulitispd.middle_useragent_wares.UAPOOLS':1
}

Scrapy核心架构

说明:

工作流

总结：

简单示例

爬取网页内容爬虫(爬取当当网特产)

创建项目及爬虫文件

scrapy startproject autopro
scrapy genspider -t basic autospd dangdang.com

编写items.py

import scrapy
 
class AutoproItem(scrapy.Item):
    name = scrapy.Field()　　　　　　#商品名称
    price = scrapy.Field()　　　　　　#商品价格
    link = scrapy.Field()　　　　　　#商品链接
    comnum = scrapy.Field()　　　　　#商品评论数量

编写爬虫文件autospd.py

# -*- coding: utf-8 -*-
import scrapy
from autopro.items import AutoproItem
from scrapy.http import Request
 
class AutospdSpider(scrapy.Spider):
    name = 'autospd'
    allowed_domains = ['dangdang.com']
    start_urls = ['http://dangdang.com/']
 
    def parse(self, response):
        item = AutoproItem()
        item['name'] = response.xpath("//a[@class='pic']/@title").extract()　　　　　　#xpath分析结果，@title表示获取titile属性的值　　
        item['price'] =response.xpath("//span[@class='price_n']/text()").extract()
        item['link'] = response.xpath("//a[@class='pic']/@href").extract()
        item['comnum'] = response.xpath("//a[@dd_name='单品评论']/text()").extract()
        yield item
        for i in range(1,10):
            url="http://category.dangdang.com/pg"+str(i)+"-cid4011029.html"
 
            yield Request(url,callback=self.parse)

编写pipelines.py

import  codecs　　　　　　　　#导入codecs模块直接进行解码
import  json
 
class AutoproPipeline(object):
 
    def __init__(self):
        self.file = codecs.open("/root/mydata.json",'wb',encoding="utf-8")　　　　#表示将爬取结果写到json文件里
 
    def process_item(self, item, spider):　　　　　　　　#process_item为pipelines中的主要处理方法，默认会自动调用
        for i in range(0,len(item["name"])):
            name = item['name'][i]
            price = item['price'][i]
            comnum = item['comnum'][i]
            link = item['link'][i]
            goods = {"name":name,"price":price,"comnum":comnum,"link":link}
            i = json.dumps(dict(goods),ensure_ascii=False)
            line = i+'\n'
            self.file.write(line)
        return item
 
    def close_spider(self,spider):
        self.file.close()

设置settings.py

ROBOTSTXT_OBEY = False        #表示不遵循robots协议
COOKIES_ENABLED = False        #禁止cookie

#开启pipelines
ITEM_PIPELINES = {
   'autopro.pipelines.AutoproPipeline': 300,
}

结果：

CrawlSpider

crawlspider是scrapy框架自带爬取网页的爬虫，可以实现网页的自动爬取

创建crawlspider 爬虫文件

crapy genspider -t crawl test_crawl jd.com

test_crawl.py

# -*- coding: utf-8 -*-
import scrapy
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule
 
class TestCrawlSpider(CrawlSpider):
    name = 'test_crawl'
    allowed_domains = ['jd.com']
    start_urls = ['http://jd.com/']
 
    #链接提取器 ,allow 为自定义设置的爬行规则，follow表示跟进爬取。即发现新的链接继续爬行,allow_domains表示允许爬行的连接
    rules = (
        Rule(LinkExtractor(allow=r'Items/'),allow_domains=(aa.com) callback='parse_item', follow=True),
    )
 
    def parse_item(self, response):
        i = {}
        #i['domain_id'] = response.xpath('//input[@id="sid"]/@value').extract()
        #i['name'] = response.xpath('//div[@id="name"]').extract()
        #i['description'] = response.xpath('//div[@id="description"]').extract()
        return i