code: def _UpdateEtag(self, response):
      
      etag = response.headers.get('etag', self.etag)
      etag_updated = self.etag != etag
      self.etag = etag
      return etag_updated
docs: Update the etag from an API response.
  
      Args:
        response: HTTP response with a header field.
  
      Returns:
        bool, True if the etag in the response header updated.