Fit the underlying estimator.

        Parameters
        ----------
        X, y : array-like
        **kwargs
            Additional fit-kwargs for the underlying estimator.

        Returns
        -------
        self : object

def fit(self, X, y=None, **kwargs):
        """Fit the underlying estimator.

        Parameters
        ----------
        X, y : array-like
        **kwargs
            Additional fit-kwargs for the underlying estimator.

        Returns
        -------
        self : object
        """
        logger.info("Starting fit")
        with _timer("fit", _logger=logger):
            result = self.estimator.fit(X, y, **kwargs)

        # Copy over learned attributes
        copy_learned_attributes(result, self)
        copy_learned_attributes(result, self.estimator)
        return self