问评分卡建模 WOE替换时报错？

源代码：
features=IV.loc[IV['IV'] > 0.001,'feature'].values
features=features.tolist()
features.append('loan_status')

for i in range(len(columns)):
    col=columns[i]
    train[col]=train[col].replace(WOEs[col])

for i in range(len(num_features)):
    col=num_features[i]
    test[col]=pd.cut(test[col],cuts[i])

for i in range(len(columns)):
    col=columns[i]
    test[col]=test[col].replace(WOEs[col])