title: Scrapy: catch responses with specific HTTP server codes
body: <p>We have a pretty much standard Scrapy project (Scrapy 0.24).</p>
  
  <p>I'd like to catch specific HTTP response codes, such as 200, 500, 502, 503, 504 etc.</p>
  
  <p>Something like that:</p>
  
  <pre><code>class Spider(...):
  
      def parse(...):
          processes HTTP 200
  
      def parse_500(...):
          processes HTTP 500 errors
  
      def parse_502(...):
          processes HTTP 502 errors
  
      ...
  </code></pre>
  
  <p>How can we do that?</p>