Does GridSearchCV not save the best parameters?

Question

So I tuned the hyperparameters using GridSearchCV, fitted the model to the data, and then used best_params_. I'm just curious why GridSearchCV takes too long to run best_params_, unlike RandomSearchCV where it instantly gives answers. The time it takes for GridSearchCV to give the best_params_ is similar to the time it takes for GridSearchCV to tune hyperparameters, and fit the model to the data. It's as if it's doing it all over again when it has done so already. Is this the case? If not, what's taking it so long when it should have saved the best_params_ when I ran GridSearchCV the first time?

Answer 1

It doesn't, please try the following code

CELL1:

import numpy as np
from sklearn import svm, datasets
from sklearn.model_selection import GridSearchCV
iris = datasets.load_iris()

CELL2:

%%time
parameters = {'kernel':('linear', 'rbf'), 'C':np.linspace(0.1,100,1000)}
svc = svm.SVC()
clf = GridSearchCV(svc, parameters)
clf.fit(iris.data, iris.target)

CELL3:

%%time
clf.best_params_

Wall time of CELL2 will be about 7-9 seconds. Wall time of CELL3 will be 0ns. ( instantaneous )

This is because best_params_ is an argument of GridSearchCV. It is however only created (and accessible) once you run .fit method.