def columns_used(self):
        return list(tz.unique(tz.concatv(
            self.choosers_columns_used(),
            self.alts_columns_used(),
            self.interaction_columns_used())))
Columns from any table used in the model. May come from either
dataset/ETHPy150Open UDST/urbansim/urbansim/models/dcm.py/MNLDiscreteChoiceModel.columns_used