使用Scrapy中的规则来抓取特定链接

Question

我正在使用scrapy从tripadvisor中搜集航空公司的评论数据。首先，我提取所有id和相应的航空公司名称。我使用以下代码仅抓取包含'Airline_Review'的链接。

import scrapy
from scrapy.selector import HtmlXPathSelector
from scrapy.spider import BaseSpider
from scrapy.http import Request
from scrapy.contrib.spiders import Rule
from scrapy.contrib.linkextractors import LinkExtractor

URL = 'http://www.tripadvisor.com'

class QuotesSpider(scrapy.Spider):
    name = "quotes"

    def start_requests(self):
        urls = [
               'https://www.tripadvisor.com/Airlines'
               ]

        rules = (
                Rule(
                    LinkExtractor(allow = '.*Airline_Review.*'),
                    callback = 'parse',
                    follow= True
                    )
                )
        for url in urls:
            yield scrapy.Request(url=url, callback=self.parse)

    def parse(self, response):
        hxs = HtmlXPathSelector(response)
        for url in hxs.select('//a/@href').extract():
            if not ( url.startswith('http://') or url.startswith('https://') ):
            url= URL + url 

            url = url.strip()
            with open('op.txt', 'a') as f:
                f.write(url)
                f.write('\n') 

            yield Request(url, callback=self.parse)

但我仍在我的op.txt文件中获取不包含'Airline_Review'的链接。我的代码中有什么不对？