code: def raise_304(instance):
      
      instance.response.status = 304
      instance.response.body = ''
      instance.response.body_raw = None
      raise ResponseException(instance.response)
docs: Abort the current request with a 304 (Not Modified) response code.
      Clears out the body of the response.
  
      :param instance: Resource instance (used to access the response)
      :type instance: :class:`webob.resource.Resource`
      :raises: :class:`webob.exceptions.ResponseException` of status 304
  
      .. todo: The following headers MUST be output: Date, ETag and/or
               Content-Location, Expires, Cache-Control, Vary. See :rfc:`2616`
               section 10.3.5.