Python3 Scrapy爬虫框架-使用CrawlSpider

• 新建项目创建爬虫

scrapy startproject Scrapy_crawl # 新建Scrapy项目

scrapy genspider -l # 查看全部模板
# Available templates:
#  basic
#  crawl
#  csvfeed
#  xmlfeed

scrapy genspider -t crawl china tech.china.com # 选择crawl模板创建爬虫
scrapy crawl china    # 运行爬虫

• CrawlSpider，其内容如下所示

# china.py
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule

class ChinaSpider(CrawlSpider):
    name = 'china'
    allowed_domains = ['tech.china.com']
    start_urls = ['http://tech.china.com/']
    # Rule的第一个参数是LinkExtractor，就是上文所说的LxmlLinkExtractor，只是名称不同。同时，默认的回调函数也不再是parse，而是parse_item
    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

• 修改start_urls链接：设置为爬取的第一个页面

start_urls = ['http://tech.china.com/articles/']

• 解析新闻链接：进入页面，F12使用开发者管理器查看源代码；所有的新闻链接都在ID为left_side节点中，具体就是每个class为con_item的节点里面；所有的新闻路径都是article开头

# allow：判断链接是否是新闻链接的正则；restrict_xpaths：检索新闻内容的正则；callback：回调函数，解析方法
Rule(LinkExtractor(allow='article\/.*\.html', restrict_xpaths='//div[@id="left_side"]//div[@class="con_item"]'), callback='parse_item')

• 分析分页链接：分页链接都在ID为pageStyle的div中，然后不断的匹配下一页的链接文本

# 提取下一页链接
Rule(LinkExtractor(restrict_xpaths='//div[@id="pageStyle"]//a[contains(., "下一页")]'))

• 重写china.py的rules

rules = (
    Rule(LinkExtractor(allow='article\/.*\.html', restrict_xpaths='//div[@id="left_side"]//div[@class="con_item"]'), callback='parse_item'),
    Rule(LinkExtractor(restrict_xpaths='//div[@id="pageStyle"]//a[contains(., "下一页")]'))
)

• 重写items.py

from scrapy import Field, Item

class NewsItem(Item):
    """新闻数据结构"""
    title = Field()  # 标题
    url = Field()  # 链接
    text = Field()  # 正文
    datetime = Field()  # 发布时间
    source = Field()  # 来源
    website = Field()  # 站点名称

• 创建loaders.py

from scrapy.loader import ItemLoader
from scrapy.loader.processors import TakeFirst, Join, Compose

class NewsLoader(ItemLoader): # 继承ItemLoader
    """TakeFirst返回列表的第一个非空值，类似extract_first()的功能"""
    default_output_processor = TakeFirst()

    class ChinaLoader(NewsLoader): # 继承NewsLoader
    """每个输入值经过Join()，再经过strip()"""
    text_out = Compose(Join(), lambda s: s.strip())
    source_out = Compose(Join(), lambda s: s.strip())

• 改写china.py的parse_item()方法：不使用通用爬虫的写法和使用通用爬虫的写法

def parse_item(self, response):
    """不使用通用爬虫CrawlSpider的写法"""
    item = NewsItem()
    item['title'] = response.xpath('//h1[@id="chan_newsTitle"]/text()').extract_first()
    item['url'] = response.url
    item['text'] = ''.join(response.xpath('//div[@id="chan_newsDetail"]//text()').extract()).strip()
    item['datetime'] = response.xpath('//div[@id="chan_newsInfo"]/text()').re_first('(\d+-\d+-\d+\s\d+:\d+:\d+)')
    item['source'] = response.xpath('//div[@id="chan_newsInfo"]/text()').re_first('来源：(.*)').strip()
    item['website'] = '中华网'
    yield item
    
def parse_item(self, response):
    loader = ChinaLoader(item=NewsItem(), response=response)  # 用该Item和Response对象实例化ItemLoader
    # 用add_xpath()、add_css()、add_value()等方法对不同属性依次赋值，最后调用load_item()方法实现Item的解析
    loader.add_xpath('title', '//h1[@id="chan_newsTitle"]/text()')
    loader.add_value('url', response.url)
    loader.add_xpath('text', '//div[@id="chan_newsDetail"]//text()')
    loader.add_xpath('datetime', '//div[@id="chan_newsInfo"]/text()', re='(\d+-\d+-\d+\s\d+:\d+:\d+)')
    loader.add_xpath('source', '//div[@id="chan_newsInfo"]/text()', re='来源：(.*)')
    loader.add_value('website', '中华网')
    yield loader.load_item()

• 上面那些步只实现的爬虫的半通用化配置
• 下面抽取爬虫的通用配置

scrapy genspider -t crawl universal universal    # 新建通用爬虫
python run.py china     # 启动爬虫

• 建立configs文件夹，与spider文件夹并列，并创建配置文件china.json

{
  "spider": "universal", # 爬虫名称
  "website": "中华网科技", # 站点名称
  "type": "新闻",    # 站点类型
  "index": "http://tech.china.com/", # 首页
  "settings": { # user_agent
    "USER_AGENT": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36"
  },
  "start_urls": [
    "http://tech.china.com/articles/"
  ],
  "allowed_domains": [
    "tech.china.com"
  ],
  "rules": "china"
}

• 新建rules.py：将所有rules单独定义在一块，实现Rule的分离

from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import Rule
rules = {
    'china': (
        Rule(LinkExtractor(allow='article\/.*\.html', restrict_xpaths='//div[@id="left_side"]//div[@class="con_item"]'),
             callback='parse_item'),
        Rule(LinkExtractor(restrict_xpaths='//div[@id="pageStyle"]//a[contains(., "下一页")]'))
    )
}

• 创建utils.py读取JSON配置文件：启动爬虫时需要读取配置文件然后动态加载到Spider中

from os.path import realpath, dirname
import json
def get_config(name):
    path = dirname(realpath(__file__)) + '/configs/' + name + '.json'
    with open(path, 'r', encoding='utf-8') as f:
        return json.loads(f.read())

• 在项目的根目录设置入库文件run.py：用来启动爬虫

import sys
from scrapy.utils.project import get_project_settings
from Scrapy_crawl.spiders.universal import UniversalSpider
from Scrapy_crawl.utils import get_config
from scrapy.crawler import CrawlerProcess
def run():
    name = sys.argv[1]  # 输入参数
    custom_settings = get_config(name)  # 获取JSON配置文件信息
    spider = custom_settings.get('spider', 'universal')  # 爬取使用的爬虫名称
    project_settings = get_project_settings()  # 声明配置
    settings = dict(project_settings.copy())
    settings.update(custom_settings.get('settings'))  # 获取到的settings配置和项目全局的settings配置做了合并
    process = CrawlerProcess(settings)  # 新建一个CrawlerProcess，传入爬取使用的配置
    process.crawl(spider, **{'name': name})  # 启动爬虫
    process.start()
if __name__ == '__main__':
    run()

• 解析方法parse_item()的可配置化，添加新配置信息到china.json中

"item": {
  "class": "NewsItem", # Item的类名
  "loader": "ChinaLoader", # Item Loader的类名
  "attrs": { # attrs属性来定义每个字段的提取规则
    "title": [
      {
        "method": "xpath", # title定义的提取方法，xpath就是相当于Item Loader的add_xpath()方法
        "args": [    # 定义匹配的正则表达式
          "//h1[@id='chan_newsTitle']/text()"
        ]
      }
    ],
    "url": [
      {
        "method": "attr", # add_value
        "args": [
          "url"
        ]
      }
    ],
    "text": [
      {
        "method": "xpath",
        "args": [
          "//div[@id='chan_newsDetail']//text()"
        ]
      }
    ],
    "datetime": [
      {
        "method": "xpath",
        "args": [
          "//div[@id='chan_newsInfo']/text()"
        ],
        "re": "(\\d+-\\d+-\\d+\\s\\d+:\\d+:\\d+)"
      }
    ],
    "source": [
      {
        "method": "xpath",
        "args": [
          "//div[@id='chan_newsInfo']/text()"
        ],
        "re": "来源：(.*)"
      }
    ],
    "website": [
      {
        "method": "value", # add_value
        "args": [
          "中华网"
        ]
      }
    ]
  }
}

• 修改配置文件china.py的start_urls参数

"start_urls": {
  "type": "static",    # 静态类型，直接配置URL列表
  "value": [
    "http://tech.china.com/articles/"
  ]
}
##############################################################################
"start_urls": {
  "type": "dynamic", # 动态类型，调用方法生成
  "method": "china",
  "args": [
    5, 10
  ]
}

• 创建urls.py类：当start_urls定义为dynamic类型，使用china()方法，只需要传入页码参数

def china(start, end):
    for page in range(start, end + 1):
        yield 'http://tech.china.com/articles/index_' + str(page) + '.html'

• 改写新建类universal.py

# -*- coding: utf-8 -*-
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule
from Scrapy_crawl.items import *
from Scrapy_crawl.loaders import *
from Scrapy_crawl.utils import get_config
from Scrapy_crawl import urls
from Scrapy_crawl.rules import rules

class UniversalSpider(CrawlSpider):
    name = 'universal'
    
    def __init__(self, name, *args, **kwargs):
        config = get_config(name)  # 获取配置文件
        self.config = config
        self.rules = rules.get(config.get('rules'))  # 获取Rule名称，然后去rules类中获取对应的Rule配置
        start_urls = config.get('start_urls')  # 获取start_urls配置
        if start_urls:
            if start_urls.get('type') == 'static':  # 静态类型，直接获取连接
                self.start_urls = start_urls.get('value')
            elif start_urls.get('type') == 'dynamic':  # 动态类型
                self.start_urls = list(eval('urls.' + start_urls.get('method'))(*start_urls.get('args', [])))
        self.allowed_domains = config.get('allowed_domains')  # 获取主机
        super(UniversalSpider, self).__init__(*args, **kwargs)

        def parse_item(self, response):
            item = self.config.get('item')  # 获取解析函数配置信息
            if item:
                cls = eval(item.get('class'))()#获取Item类
                loader = eval(item.get('loader'))(cls, response=response)#获取loader
                # 动态获取属性配置
                for key, value in item.get('attrs').items():
                    for extractor in value:
                        if extractor.get('method') == 'xpath':
                            loader.add_xpath(key, *extractor.get('args'), **{'re': extractor.get('re')})
                        if extractor.get('method') == 'css':
                            loader.add_css(key, *extractor.get('args'), **{'re': extractor.get('re')})
                        if extractor.get('method') == 'value':
                            loader.add_value(key, *extractor.get('args'), **{'re': extractor.get('re')})
                        if extractor.get('method') == 'attr':
                            loader.add_value(key, getattr(response, *extractor.get('args')))
                yield loader.load_item()

• https://github.com/My-Sun-Shine/Python/tree/master/Python3/Scrapy_Learn/Scrapy_crawl