model = SelectKBest(chi2)
n_components = [3,4,5,6,7,8]
param_grid = dict(k=n_components)
grid_search = GridSearchCV(model,param_grid,scoring = 'accuracy')
m1 = grid_search.fit(x_train, y_train)
print(" Best_score： %.4lf" %grid_search.best_score_)
print(" Best_params：", grid_search.best_params_)