title: Empty list returning by xpath in scrapy
body: <p>I am working on scrapy , i am trying to gather some data from a site , </p>
  
  <p><strong>Spider Code</strong></p>
  
  <pre><code>class NaaptolSpider(BaseSpider):
      name = "naaptol"
      domain_name = "www.naaptol.com"
      start_urls = ["http://www.naaptol.com/buy/mobile_phones/mobile_handsets.html"]
  
      def parse(self, response):
          hxs = HtmlXPathSelector(response)
          cell_matter = hxs.select('//div[@class="gridInfo"]/div[@class="gridProduct gridProduct_special"]')
          items=[]
          for i in cell_matter:
                 cell_names = i.select('//p[@class="proName"]/a/text()').extract()
                 prices = i.select('//p[@class="values"]/strong/text()').extract()
                 item = ExampleItem()
                 item['cell_name'] = cell_names
                 item['price'] = prices
                 items.append(item) 
          return [FormRequest(url="http://www.naaptol.com/faces/jsp/search/searchResults.jsp",
              formdata={'type': 'cat_catlg',
              'catid': '27',
              'sb' : '9,8',
              'frm' : '1',
              'max' : '15',
              'req': 'ajax'
              },
              callback=self.parse_item
              )]
  
  def parse_item(self, response):
       hxs = HtmlXPathSelector(response) 
       cell_matter = hxs.select('//div[@class="gridInfo"]/div[@class="gridProduct gridProduct_special"]')
       for i in cell_matter:
                 cell_names = i.select('//p[@class="proName"]/a/text()').extract()
                 prices = i.select('//p[@class="values"]/strong/text()').extract()
                 print cell_names
                 print prices 
  </code></pre>
  
  <p><strong>Result:</strong></p>
  
  <pre><code>2012-06-15 09:38:36+0530 [naaptol] DEBUG: Crawled (200) &lt;POST http://www.naaptol.com/faces/jsp/search/searchResults.jsp&gt; (referer: http://www.naaptol.com/buy/mobile_phones/mobile_handsets.html)
  []
  []
  </code></pre>
  
  <p>Actually i had posted the form to achieve the pagination which is in javascript</p>
  
  <p>Here i am receiving the response from parse method in parse_item method, but when i used the xpath same as in parse method its returning an empty list as above, can anyone tell me why its returning an empty array, and whats wrong in my code.</p>
  
  <p>Thanks in advance </p>