I have 2 questions regarding cross_val_score.

1. Do the scores returned by cross_val_score correspond to only the test set or the whole data set (training and test sets)?

I tried to look at the source code, and it looks like it returns the score of only the test set (line 145: "return_train_score=False") - I am not sure if I am reading the codes properly, though..

I came across the paper below and the authors use the score of the whole dataset when the author performs repeated nested loop, grid search cv, etc.. e.g. see algorithm 1 (line 1c) and 2 (line 2d) on page 3.

2. On line 283 of the cross_val_score source code, there is a function _score. However, I can't find where this function is called. Could you let me know where this function is called?

Thank you very much!

Raga