https://scikit-learn.org/dev/modules/cross_validation.html#cross-validation
这个官方文档写得太好了
概念
Here is a flowchart of typical cross validation workflow in model training.
k折交叉验证解释：
cross_val_score 和cross_validate
https://scikit-learn.org/dev/modules/cross_validation.html#computing-cross-validated-metrics
可以传给scoring的度量：
https://scikit-learn.org/stable/modules/model_evaluation.html#scoring-parameter
