title: find element has the class or not in scrapy
body: <p>I am new in scrapy.</p>
  <p>I get list of li tag from xpath selector : <code>categories = categories_container.xpath('li')</code>
  now I have find out which category element has the css class of &quot;particular class which not in other li&quot;.</p>
  <p>what I can do to find that li ?</p>
  <p>thanks in advance.</p>