def __init__(self, right_col, left_col, right_cardinality=None, left_cardinality=None):
        if right_cardinality not in self.cardinalities.keys()\
           or left_cardinality not in self.cardinalities.keys():
            raise ValueError('Cardinality should be in {}"'.format(self.cardinalities.keys()))
        self.right_col = right_col
        self.left_col = left_col
        self.right_cardinality = right_cardinality
        self.left_cardinality = left_cardinality
dataset/ETHPy150Open Alexis-benoist/eralchemy/eralchemy/models.py/Relation.__init__/original