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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _can_update(self):
 """ Called by the save function to check if this should be persisted with update or insert :return: """

        if not self._is_persisted: return False
        pks = self._primary_keys.keys()
        return all([not self._values[k].changed for k in self._primary_keys])