I'm trying to get mean test scores from scikit-learn's GridSearchCV with multiple scorers.

grid.cv_results_ displays lots of info. But grid.cv_results_['mean_test_score'] keeps giving me an error.

I've checked the docs and similar questions with no luck. What am I doing wrong?


scorers = {
    'r2': 'r2',
    'nmsle': 'neg_mean_squared_log_error',
    'nmse': 'neg_mean_squared_error'

params = [
        'regressor': [GradientBoostingRegressor()], 'preprocessing': [None],

grid = GridSearchCV(pipe, params, cv=5, scoring=scorers, refit='nmse')
grid.fit(X_t, y_train)



KeyError                                  Traceback (most recent call last)
<ipython-input-161-a021fe7b05bb> in <module>
     20 print(f'Val score set score rmse: {rm}')
---> 22 grid.cv_results_['mean_test_score']
     24 # for mean in means:

~/anaconda3/lib/python3.6/site-packages/sklearn/utils/deprecation.py in __getitem__(self, key)
    124             warn_args, warn_kwargs = self._deprecations[key]
    125             warnings.warn(*warn_args, **warn_kwargs)
--> 126         return super(DeprecationDict, self).__getitem__(key)
    128     def get(self, key, default=None):

KeyError: 'mean_test_score'

1 Answer 1


For multi-metric evaluation, the scores for all the scorers are available in the cv_results_ dict at the keys ending with that scorer's name ('_scorer_name'). so use


Ex: grid.cv_results_['mean_test_r2']

  • $\begingroup$ Thanks! That's easy. Where did you find the answer? $\endgroup$
    – jeffhale
    Jan 10, 2019 at 20:01
  • 1
    $\begingroup$ scikit learn documentation $\endgroup$
    – Uday
    Jan 10, 2019 at 20:15
  • $\begingroup$ I am getting a key error trying this. I don't get why $\endgroup$
    – Atirag
    Feb 5, 2021 at 18:26

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