Python爬虫-Scrapy框架之CrawlSpider

  背景：在糗事百科的爬虫案例中，我们是自己在解析完整个页面后获取到下一页的url，然后重新发送一个请求。有时候我们想要这样做，只要满足某个条件的url，都给我进行爬取，那么这时候我们就可以通过CrawlSpider来帮我们完成。CrawlSpider继承自Spider，只不过是在之前的基础之上增加了新的功能。

1、创建CrawlSpider爬虫

  之前创建爬虫的方式是通过scrapy genspider [爬虫名字] [域名]的方式创建的，如果想要创建CrawlSpider爬虫，那么应该通过命令scrapy genspider -t crawl [爬虫名字] [域名]创建。

2、LinkExtractors链接提取器

  使用LinkExtractors可以不用程序员自己提取想要的url，然后发送请求，这些工作都可以交给LinkExtractors，他会在所有爬的页面中找到满足规则的url，实现自动爬取。

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
)

  主要参数说明：
  1）allow：允许的url，所有满足这个正则表达式的url都会被提取；
  2）deny：禁止的url，所有满足这个正则表达式的url都不会被提取；
  3）allow_domains：允许的域名，只有在这个里面指定的域名的url才会被提取；
  4）deny_domains：禁止的域名，所有在这个里面指定的域名的url都不会被提取；
  5）restrict_xpaths：严格的xpath，和allow共同过滤链接。

3、Rule规则类

  定义爬虫的规则类。

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

  主要参数说明：
  1）link_extractor：一个LinkExtractor对象，用于定义爬取规则；
  2）callback：满足这个规则的url，应该要执行哪个回调函数，因为CrawlSpider使用了parse作为回调函数，因此不要覆盖parse，用自己的回调函数作为回调函数；
  3）follow：指定根据该规则从response中提取的链接是否需要跟进；
  4）process_links：从link_extractor中获取到链接后会传递给这个函数，用来过滤不需要爬取的链接。

4、爬虫实例（微信小程序社区）

4.1、创建项目

D:\学习笔记\Python学习\Python_Crawler>scrapy startproject wxapp
New Scrapy project 'wxapp', using template directory 'c:\python38\lib\site-packages\scrapy\templates\project', created in:
    D:\学习笔记\Python学习\Python_Crawler\wxapp

You can start your first spider with:
    cd wxapp
    scrapy genspider example example.com

4.2、创建爬虫

D:\学习笔记\Python学习\Python_Crawler>cd wxapp

D:\学习笔记\Python学习\Python_Crawler\wxapp>scrapy genspider -t crawl wxappSpider "wxapp-union.com"
Created spider 'wxappSpider' using template 'crawl' in module:
  wxapp.spiders.wxappSpider

Scrapy项目目录结构

  spiders/init.py文件初始内容：

# 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文件初始内容：

# -*- 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文件初始内容：

# -*- 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文件初始内容：

# -*- 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文件初始内容：

# -*- 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文件初始内容：

# -*- 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文件初始内容：

# 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、代码实现

  需要使用LinkExtractor和Rule，这两个类决定了爬虫的具体走向。
  1）allow设置规则的方法：要能够限制在我们的想要的url上面，不要跟其他的url产生相同的正则表达式即可；
  2）什么情况下使用follow：如果在爬取页面的时候，需要将满足当前条件的url再进行跟进，那么就设置为True，否则设置为False；
  3）什么情况下该指定callback：如果这个url对应的页面，只是为了获取更多的url，并不需要里面的数据，那么可以不指定callback。

  A）settings.py设置

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）创建start.py文件
 &esmp;在项目的根目录下创建start.py文件，并编写代码。

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

  C）wxappSpider.py代码如下：

# -*- 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"//h1[@class='ph']/text()").get().strip()
        p = response.xpath(r"//p[@class='authors']")
        author = p.xpath(r".//a/text()").get().strip()
        pubTime = p.xpath(r".//span/text()").get().strip()
        articleContent = response.xpath(r"//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代码如下：

# -*- 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代码如下：

# -*- 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()