Python爬蟲-Scrapy框架之CrawlSpider

??背景：在糗事百科的爬蟲案例中，我們是自己在解析完整個(gè)頁(yè)面后獲取到下一頁(yè)的url，然后重新發(fā)送一個(gè)請(qǐng)求。有時(shí)候我們想要這樣做，只要滿足某個(gè)條件的url，都給我進(jìn)行爬取，那么這時(shí)候我們就可以通過(guò)CrawlSpider來(lái)幫我們完成。CrawlSpider繼承自Spider，只不過(guò)是在之前的基礎(chǔ)之上增加了新的功能。

1、創(chuàng)建CrawlSpider爬蟲

??之前創(chuàng)建爬蟲的方式是通過(guò)scrapy genspider [爬蟲名字] [域名]的方式創(chuàng)建的，如果想要?jiǎng)?chuàng)建CrawlSpider爬蟲，那么應(yīng)該通過(guò)命令scrapy genspider -t crawl [爬蟲名字] [域名]創(chuàng)建。

2、LinkExtractors鏈接提取器

??使用LinkExtractors可以不用程序員自己提取想要的url，然后發(fā)送請(qǐng)求，這些工作都可以交給LinkExtractors，他會(huì)在所有爬的頁(yè)面中找到滿足規(guī)則的url，實(shí)現(xiàn)自動(dòng)爬取。

class LxmlLinkExtractor(
    allow=(), 
    deny=(), 
    allow_domains=(), 
    deny_domains=(), 
    restrict_xpaths=(),
    tags=('a', 'area'), 
    attrs=('href',), 
    canonicalize=False,
    unique=True, 
    process_value=None, 
    deny_extensions=None, 
    restrict_css=(),
    strip=True, 
    restrict_text=None
)

??主要參數(shù)說(shuō)明：
??1）allow：允許的url，所有滿足這個(gè)正則表達(dá)式的url都會(huì)被提??；
??2）deny：禁止的url，所有滿足這個(gè)正則表達(dá)式的url都不會(huì)被提??；
??3）allow_domains：允許的域名，只有在這個(gè)里面指定的域名的url才會(huì)被提?。?br> ??4）deny_domains：禁止的域名，所有在這個(gè)里面指定的域名的url都不會(huì)被提?。?br> ??5）restrict_xpaths：嚴(yán)格的xpath，和allow共同過(guò)濾鏈接。

3、Rule規(guī)則類

??定義爬蟲的規(guī)則類。

class Rule(
    link_extractor=None, 
    callback=None, 
    cb_kwargs=None, 
    follow=None,
    process_links=None, 
    process_request=None, 
    errback=None
)

??主要參數(shù)說(shuō)明：
??1）link_extractor：一個(gè)LinkExtractor對(duì)象，用于定義爬取規(guī)則；
??2）callback：滿足這個(gè)規(guī)則的url，應(yīng)該要執(zhí)行哪個(gè)回調(diào)函數(shù)，因?yàn)?code>CrawlSpider使用了parse作為回調(diào)函數(shù)，因此不要覆蓋parse，用自己的回調(diào)函數(shù)作為回調(diào)函數(shù)；
??3）follow：指定根據(jù)該規(guī)則從response中提取的鏈接是否需要跟進(jìn)；
??4）process_links：從link_extractor中獲取到鏈接后會(huì)傳遞給這個(gè)函數(shù)，用來(lái)過(guò)濾不需要爬取的鏈接。

4、爬蟲實(shí)例（微信小程序社區(qū)）

4.1、創(chuàng)建項(xiàng)目
D:\學(xué)習(xí)筆記\Python學(xué)習(xí)\Python_Crawler>scrapy startproject wxapp
New Scrapy project 'wxapp', using template directory 'c:\python38\lib\site-packages\scrapy\templates\project', created in:
    D:\學(xué)習(xí)筆記\Python學(xué)習(xí)\Python_Crawler\wxapp

You can start your first spider with:
    cd wxapp
    scrapy genspider example example.com
4.2、創(chuàng)建爬蟲
D:\學(xué)習(xí)筆記\Python學(xué)習(xí)\Python_Crawler>cd wxapp

D:\學(xué)習(xí)筆記\Python學(xué)習(xí)\Python_Crawler\wxapp>scrapy genspider -t crawl wxappSpider "wxapp-union.com"
Created spider 'wxappSpider' using template 'crawl' in module:
  wxapp.spiders.wxappSpider
Scrapy項(xiàng)目目錄結(jié)構(gòu)

??spiders/init.py文件初始內(nèi)容：

# This package will contain the spiders of your Scrapy project
#
# Please refer to the documentation for information on how to create and manage
# your spiders.

??spiders/wxappSpider.py文件初始內(nèi)容：

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


class WxappspiderSpider(CrawlSpider):
    name = 'wxappSpider'
    allowed_domains = ['wxapp-union.com']
    start_urls = ['http://wxapp-union.com/']

    rules = (
        Rule(LinkExtractor(allow=r'Items/'), callback='parse_item', follow=True),
    )

    def parse_item(self, response):
        item = {}
        #item['domain_id'] = response.xpath('//input[@id="sid"]/@value').get()
        #item['name'] = response.xpath('//div[@id="name"]').get()
        #item['description'] = response.xpath('//div[@id="description"]').get()
        return item

??items.py文件初始內(nèi)容：

# -*- 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 WxappItem(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    pass

??middlewares.py文件初始內(nèi)容：

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

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

from scrapy import signals


class WxappSpiderMiddleware:
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the spider middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_spider_input(self, response, spider):
        # Called for each response that goes through the spider
        # middleware and into the spider.

        # Should return None or raise an exception.
        return None

    def process_spider_output(self, response, result, spider):
        # Called with the results returned from the Spider, after
        # it has processed the response.

        # Must return an iterable of Request, dict or Item objects.
        for i in result:
            yield i

    def process_spider_exception(self, response, exception, spider):
        # Called when a spider or process_spider_input() method
        # (from other spider middleware) raises an exception.

        # Should return either None or an iterable of Request, dict
        # or Item objects.
        pass

    def process_start_requests(self, start_requests, spider):
        # Called with the start requests of the spider, and works
        # similarly to the process_spider_output() method, except
        # that it doesn’t have a response associated.

        # Must return only requests (not items).
        for r in start_requests:
            yield r

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)


class WxappDownloaderMiddleware:
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the downloader middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_request(self, request, spider):
        # Called for each request that goes through the downloader
        # middleware.

        # Must either:
        # - return None: continue processing this request
        # - or return a Response object
        # - or return a Request object
        # - or raise IgnoreRequest: process_exception() methods of
        #   installed downloader middleware will be called
        return None

    def process_response(self, request, response, spider):
        # Called with the response returned from the downloader.

        # Must either;
        # - return a Response object
        # - return a Request object
        # - or raise IgnoreRequest
        return response

    def process_exception(self, request, exception, spider):
        # Called when a download handler or a process_request()
        # (from other downloader middleware) raises an exception.

        # Must either:
        # - return None: continue processing this exception
        # - return a Response object: stops process_exception() chain
        # - return a Request object: stops process_exception() chain
        pass

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)

??pipelines.py文件初始內(nèi)容：

# -*- 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 WxappPipeline:
    def process_item(self, item, spider):
        return item

??settings.py文件初始內(nèi)容：

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

# Scrapy settings for wxapp 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 = 'wxapp'

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


# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'wxapp (+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://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 = {
#    'wxapp.middlewares.WxappSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'wxapp.middlewares.WxappDownloaderMiddleware': 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 = {
#    'wxapp.pipelines.WxappPipeline': 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'

??scrapy.cfg文件初始內(nèi)容：

# Automatically created by: scrapy startproject
#
# For more information about the [deploy] section see:
# https://scrapyd.readthedocs.io/en/latest/deploy.html

[settings]
default = wxapp.settings

[deploy]
#url = http://localhost:6800/
project = wxapp
4.3、代碼實(shí)現(xiàn)

??需要使用LinkExtractor和Rule，這兩個(gè)類決定了爬蟲的具體走向。
??1）allow設(shè)置規(guī)則的方法：要能夠限制在我們的想要的url上面，不要跟其他的url產(chǎn)生相同的正則表達(dá)式即可；
??2）什么情況下使用follow：如果在爬取頁(yè)面的時(shí)候，需要將滿足當(dāng)前條件的url再進(jìn)行跟進(jìn)，那么就設(shè)置為True，否則設(shè)置為False；
??3）什么情況下該指定callback：如果這個(gè)url對(duì)應(yīng)的頁(yè)面，只是為了獲取更多的url，并不需要里面的數(shù)據(jù)，那么可以不指定callback。

??A）settings.py設(shè)置

ROBOTSTXT_OBEY = False

DOWNLOAD_DELAY = 1

DEFAULT_REQUEST_HEADERS = {
    'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
    'Accept-Language': 'en',
    'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.9 Safari/537.36',
}

ITEM_PIPELINES = {
   'qiushibk.pipelines.QiushibkPipeline': 300,
}

??B）創(chuàng)建start.py文件
?&esmp;在項(xiàng)目的根目錄下創(chuàng)建start.py文件，并編寫代碼。

from scrapy import cmdline
cmdline.execute("scrapy crawl wxappSpider".split())

??C）wxappSpider.py代碼如下：

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

class WxappspiderSpider(CrawlSpider):
    name = 'wxappSpider'
    allowed_domains = ['wxapp-union.com']
    start_urls = ['http://www.wxapp-union.com/portal.php?mod=list&catid=2&page=1']

    rules = (
        Rule(LinkExtractor(allow=r'.+mod=list&catid=2&page=\d'), follow=True),
        Rule(LinkExtractor(allow=r'.+article-.+\.html'), callback='parse_item', follow=False)
    )

    def parse_item(self, response):
        title = response.xpath(r"http://h1[@class='ph']/text()").get().strip()
        p = response.xpath(r"http://p[@class='authors']")
        author = p.xpath(r".//a/text()").get().strip()
        pubTime = p.xpath(r".//span/text()").get().strip()
        articleContent = response.xpath(r"http://td[@id='article_content']//text()").getall()
        content = "".join(articleContent).strip()
        item = WxappItem(title=title, author=author, pubTime=pubTime, content=content)
        yield item

??D）items.py代碼如下：

# -*- 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 WxappItem(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    title = scrapy.Field()
    author = scrapy.Field()
    pubTime = scrapy.Field()
    content = scrapy.Field()

??E）pipelines.py代碼如下：

# -*- 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

from scrapy.exporters import JsonLinesItemExporter

class WxappPipeline:
    def __init__(self):
        self.fp = open('wxjc.json', 'wb')
        self.exporter = JsonLinesItemExporter(self.fp, ensure_ascii=False, encoding='utf-8')

    def process_item(self, item, spider):
        self.exporter.export_item(item)
        return item

    def close_spider(self):
        self.fp.close()
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