def _is_ndb(self):
"""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.
"""
# 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 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: %s.' %
(self._model,))
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