Я пытаюсь запустить этот код, но я получаю сообщение об ошибке «TypeError: unhashable type: 'set' '?

Question

Я пытаюсь запустить этот код, но я получаю сообщение об ошибке

TypeError: unhashable тип: 'set'

def exhaustive(model,train_X,train_y,valid_X,valid_y):
    low_err=600000**2

    for x in range(len(train_X.columns),0,-1):
        n=x
        #print("number of features "+str(n))
        ss=findsubsets(train_X.columns,n)
        print("_"*50)
        print(str(len(ss))+" model(s) using "+ str(n)+ " features")
        for z in range(0,len(ss)):

            model = model
            reg  = model.fit(train_X[ss[z]], train_y)
            pred_train = reg.predict(train_X[ss[z]])
            err_train= mean_squared_error(train_y, pred_train)


            pred_valid = reg.predict(valid_X[ss[z]])
            err_valid = mean_squared_error(valid_y, pred_valid)
            mae_valid = mean_absolute_error(valid_y,pred_valid)    

            if err_valid < low_err:
                low_err=err_valid
                low_err_features=list(ss[z])
                print("_"*50)
                print(low_err_features)
                print("RMSE train: "+str(err_train ** .5))
                print("MSE validation: "+str(low_err))
                print("RMSE validation: "+str(low_err ** .5))
                print("MAE validation: "+str(mae_valid))
                abs(valid_y-pred_valid).hist()
                plt.show()
                print("_"*50)
exhaustive(model=LinearRegression(normalize=False,n_jobs=-1), train_X=train_X, train_y=train_y, valid_X=valid_X, valid_y=valid_y)