UnboundLocalError: local variable 'best_idx' referenced before assignment

[Salidor]

In Training phase i get this error:

UnboundLocalError                         Traceback (most recent call last)

<ipython-input-30-730ad33b5889> in <module>()
    110     model.train(False)  # evaluation을 위해, 훈련 X
    111     #global best_idx
--> 112     best_train_F, new_train_F, _,_ = evaluating(model, test_train_data, best_train_F, epoch)
    113     best_test_F,  new_test_F,  _,opts.best_idx = evaluating(model, test_data, best_test_F, epoch)
    114     # validation의 결과가 best면 save를 True로, 모델이 저장되도록

<ipython-input-29-76c9c4a8fd6b> in evaluating(model, datas, best_F, epoch, display_confusion_matrix)
    118     # new_F : 현재 sample의   F score
    119     # save  : 최고 F score를 갱신하면 save = True를 return
--> 120     return best_F, new_F, save, best_idx
    121     print(best_idx)

UnboundLocalError: local variable 'best_idx' referenced before assignment

Any idea how to solve it?