title: Scrapy, Python: Multiple Item Classes in one pipeline?
body: <p>I have a Spider that scrapes data which cannot be saved in one item class.</p>
  <p>For illustration, I have one Profile Item, and each Profile Item might have an unknown number of Comments. That is why I want to implement Profile Item and Comment Item. I know I can pass them to my pipeline simply by using yield.</p>
  <ol>
  <li><p>However, I do not know how a pipeline with one parse_item function can handle two different item classes?</p>
  </li>
  <li><p>Or is it possible to use different parse_item functions?</p>
  </li>
  <li><p>Or do I have to use several pipelines?</p>
  </li>
  <li><p>Or is it possible to write an Iterator to a Scrapy Item Field?</p>
  </li>
  </ol>
  <hr />
  <pre><code>comments_list=[]
  comments=response.xpath(somexpath)
  for x in comments.extract():
          comments_list.append(x)
      ScrapyItem['comments'] =comments_list
  </code></pre>