def _prepare_for_put(self, entity):
    if (self._auto_now or
        (self._auto_now_add and not self._has_value(entity))):
      value = self._now()
      self._store_value(entity, value)
dataset/ETHPy150Open GoogleCloudPlatform/datastore-ndb-python/ndb/model.py/DateTimeProperty._prepare_for_put/original