code: def get_compatibility(self, subject=None):
          
          url = '/'.join([self.url, 'config'])
          if subject:
              url = '/'.join([url, subject])
  
          result, code = self._send_request(url)
          is_successful_request = code >= 200 and code <= 299
          if not is_successful_request:
              raise ClientError('Unable to fetch compatibility level. Error code: %d' % code)
  
          compatibility = result.get('compatibilityLevel', None)
          if compatibility not in VALID_LEVELS:
              if compatibility is None:
                  error_msg_suffix = 'No compatibility was returned'
              else:
                  error_msg_suffix = str(compatibility)
              raise ClientError('Invalid compatibility level received: %s' % error_msg_suffix)
  
          return compatibility
docs: GET /config
          Get the current compatibility level for a subject.  Result will be one of:
  
          :param str subject: subject name
          :raises ClientError: if the request was unsuccessful or an invalid compatibility level was returned
          :returns: one of 'NONE','FULL','FORWARD', or 'BACKWARD'
          :rtype: bool