def initialize(self, state, dict_):

        _, user_data = self._initialize_collection(state)
        dict_[self.key] = user_data
        return user_data
Initialize this attribute with an empty collection.
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py/CollectionAttributeImpl.initialize