code: def _is_ndb(self):
          
          # issubclass will fail if one of the arguments is not a class, only
          # need worry about new-style classes since ndb and db models are
          # new-style
          if isinstance(self._model, type):
              if _NDB_MODEL is not None and issubclass(self._model, _NDB_MODEL):
                  return True
              elif issubclass(self._model, db.Model):
                  return False
  
          raise TypeError(
              'Model class not an NDB or DB model: {0}.'.format(self._model))
docs: Determine whether the model of the instance is an NDB model.
  
          Returns:
              Boolean indicating whether or not the model is an NDB or DB model.