code: def _get_request_representer(self):
          
          try:
              mime_type = \
                get_registered_mime_type_for_string(self.request.content_type)
          except KeyError:
              # The client sent a content type we do not support (415).
              raise HTTPUnsupportedMediaType()
          return as_representer(self.context, mime_type)
docs: Returns a representer for the content type specified in the request.
  
          :raises HTTPUnsupportedMediaType: If the specified content type is
            not supported.