Как создать экземпляр scrapy.http.Response из строки URL?

Чтобы получить данные, которые мне нужны с веб-сайта с помощью scrapy, мне сначала нужно создать объект ответа, чтобы я мог использовать HtmlXpathSelector на нем. HtmlXpathSelector не принимает строку url в качестве аргумента. В следующем примере кода переменная "response2" пуста, потому что я не знаю, как это сделать.

from scrapy.selector import HtmlXPathSelector
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.contrib.spiders import CrawlSpider, Rule
from tarantula.items import OlgaItem

class OlgaSpider(CrawlSpider):
    """This crawler gets the physician name and his homepage url."""

    name = 'Olga'
    DOWNLOAD_DELAY = 6 #para tentar evitar ser banido
    #ROBOTSTXT_OBEY = True
    #CONCURRENT_REQUESTS = 1
    FEED_URI = '/home/mercutio22/gitcode/MedicWebsites.csv'
    FEED_FORMAT = 'csv'
    USER_AGENT = "Googlebot/2.1 ( http://www.google.com/bot.html )"
    #allowed_domains = ['guiareunimedicos.med.br']
    start_urls = (
    'http://medial-saude.guiareunimedicos.med.br/index.pl?act=searc\
    h&_id_=172&_ev_=Submit&_formSearchSubmit=%3Adefault%3A&type=0&country=0\
    &q=oncologia#results/',
   'http://www.guiareunimedicos.med.br/index.pl?act=search&_id_=17\
    #2&_ev_=Submit&_formSearchSubmit=%3Adefault%3A&type=0&country=0&q=cancer\
    #ologia#results/' )
    rules = (
    Rule(SgmlLinkExtractor(allow=r"V=", restrict_xpaths='//a[text()=">"]'),
    callback='parse_item', follow=True),
     )

   def parse_item(self, response):

       hxs = HtmlXPathSelector(response)
       mdata = hxs.select('//div[contains(@class, "mdata")]')
       links = mdata.select('./a/@href').extract()
       names = mdata.select('./a/text()').extract()

       items = []
       for index in range(len(names)):
           i = OlgaItem()
           i['name'] = names[index]
           i['link'] = links[index]
           response2 = 
           hxs2 = HtmlXPathSelector(response2) ###
           name = hxs2.select('//big/text()').extract()
           i['clinics'] = hxs2.select('//h2/a/text()').extract()
           data = hxs2.select('//div[contains(@class, "stab data")]')
           addresses = [ x.select('./p/text()').extract() for x in data ]
           addresses = [ ''.join(x) for x in addresses ]
           addresses = [ x.replace('Telefone(s): \r\n\r\n\r\n', '') for x in addresses ]
           addresses = [ x[2:] for x in addresses ]
           i['addresses'] = addresses
           i['phones']  = hxs2.select('//span[@id]/text()').extract()

           items.append(i)
       return items