Selector有四个基本的方法:
xpath(): 传入xpath表达式，返回该表达式所对应的所有节点的selector list列表 。css(): 传入CSS表达式，返回该表达式所对应的所有节点的selector list列表.extract(): 序列化该节点为unicode字符串并返回list。re(): 根据传入的正则表达式对数据进行提取，返回unicode字符串list列表。
shell根据response提前初始化了变量 sel 。该selector根据response的类型自动选择最合适的分析规则(XML vs HTML)。
In [1]: sel.xpath('//title')
Out[1]: [<Selector xpath='//title' data=u'<title>Open Directory - Computers: Progr'>]
In [2]: sel.xpath('//title').extract()
Out[2]: [u'<title>Open Directory - Computers: Programming: Languages: Python: Books</title>']
In [3]: sel.xpath('//title/text()')
Out[3]: [<Selector xpath='//title/text()' data=u'Open Directory - Computers: Programming:'>]
In [4]: sel.xpath('//title/text()').extract()
Out[4]: [u'Open Directory - Computers: Programming: Languages: Python: Books']
In [5]: sel.xpath('//title/text()').re('(\w+):')
Out[5]: [u'Computers', u'Programming', u'Languages', u'Python']
简单spider demo
import scrapy
from tutorial.items import DmozItem
class DmozSpider(scrapy.spiders.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() #创建item对象 已字典方式放回给item item['title'] = sel.xpath('a/text()').extract() item['link'] = sel.xpath('a/@href').extract() item['desc'] = sel.xpath('text()').extract() yield item
