1. 安装Scrapy
  2. 创建一个Scrapy项目
  3. 编写一个爬虫Spider
  4. 运行Scrapy
  5. 定义保存爬取到的数据的容器Item
  6. 提取Item

Scrapy是一个为了爬取网站数据，提取结构性数据而编写的Python应用框架。

详情见 http://scrapy.org/

文档：http://doc.scrapy.org/en/latest/

中文文档：http://scrapy-chs.readthedocs.io/zh_CN/latest/

Scrapy例子项目：https://github.com/lijiancheng0614/ScrapyExamples

安装Scrapy

安装了python后只需在命令行中输入以下命令：

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pip install scrapy

创建一个Scrapy项目

新建一个叫tutorial的Scrapy项目，在命令行中输入：

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scrapy startproject tutorial

得到tutorial目录：

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tutorial/
    scrapy.cfg            # deploy configuration file
    tutorial/             # project's Python module, you'll import your code from here
        __init__.py
        items.py          # project items file
        pipelines.py      # project pipelines file
        settings.py       # project settings file
        spiders/          # a directory where you'll later put your spiders
            __init__.py
            ...

编写一个爬虫Spider

创建tutorial/spiders/dmoz_spider.py（或在命令行中输入scrapy genspider dmoz dmoz.org），输入以下内容：

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import scrapy

class DmozSpider(scrapy.Spider):
    name = "dmoz"
    allowed_domains = ["dmoz.org"]
    start_urls = [
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
    ]

    def parse(self, response):
        filename = response.url.split("/")[-2] + '.html'
        with open(filename, 'wb') as f:
            f.write(response.body)

运行Scrapy

在tutorial下命令行中输入：

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scrapy crawl dmoz

得到类似的输出：

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2014-01-23 18:13:07-0400 [scrapy] INFO: Scrapy started (bot: tutorial)
2014-01-23 18:13:07-0400 [scrapy] INFO: Optional features available: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Overridden settings: {}
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled extensions: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled downloader middlewares: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled spider middlewares: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled item pipelines: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Spider opened
2014-01-23 18:13:08-0400 [scrapy] DEBUG: Crawled (200) <GET http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/> (referer: None)
2014-01-23 18:13:09-0400 [scrapy] DEBUG: Crawled (200) <GET http://www.dmoz.org/Computers/Programming/Languages/Python/Books/> (referer: None)
2014-01-23 18:13:09-0400 [scrapy] INFO: Closing spider (finished)

并在tutorial目录中得到Resources.html和Books.html文件。

定义保存爬取到的数据的容器Item

编辑tutorial/items.py，输入以下内容：

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import scrapy

class DmozItem(scrapy.Item):
    title = scrapy.Field()
    link = scrapy.Field()
    desc = scrapy.Field()

提取Item

从网页中提取数据有很多方法。Scrapy使用了一种基于XPath和CSS表达式机制:Scrapy Selectors。关于selector和其他提取机制的信息请参考Selector文档。

修改tutorial/spiders/dmoz_spider.py：

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import scrapy

from tutorial.items import DmozItem

class DmozSpider(scrapy.Spider):
    name = "dmoz"
    allowed_domains = ["dmoz.org"]
    start_urls = [
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
    ]

    def parse(self, response):
        for sel in response.xpath('//ul/li'):
            item = DmozItem()
            item['title'] = sel.xpath('a/text()').extract()
            item['link'] = sel.xpath('a/@href').extract()
            item['desc'] = sel.xpath('text()').extract()
            yield item

在tutorial下命令行中输入：

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scrapy crawl dmoz -o items.json
scrapy crawl dmoz -o items.csv

即可得到相应的json文件和csv文件。