code: def clean_etag(self, etag):
          
          if etag:
              etag = etag.replace('"', '')
              extension = None
              for ext, mime in self.EXTENSION_MAP:
                  if mime == self.type:
                      extension = ext[1:]
                      break
              if extension:
                  etag += '_' + extension
              self.response.etag = etag
docs: Cleans the ETag as returned by :func:`get_etag`. Will wrap it in
          quotes and append the extension for the current MIME type.