g scorer.

    .. versionadded:: 1.5
        Only available if `enable_metadata_routing=True`,
        which can be set by using
        ``sklearn.set_config(enable_metadata_routing=True)``.
        See :ref:`Metadata Routing User Guide <metadata_routing>` for
        more details.

Returns
-------
self : object
    Fitted estimator.

Notes
-----
When sample_weight is provided, the selected hyperparameter may depend
on whether we use leave-one-out cross-validation (cv=None or cv='auto')
or another form of cross-validation, because only leave-one-out
cross-validation takes the sample weights into account when computing
the validation score.
r4