Set init score of Booster to start from.

        Parameters
        ----------
        init_score : list, numpy 1-D array, pandas Series or None
            Init score for Booster.

        Returns
        -------
        self : Dataset
            Dataset with set init score.

def set_init_score(self, init_score):
        """Set init score of Booster to start from.

        Parameters
        ----------
        init_score : list, numpy 1-D array, pandas Series or None
            Init score for Booster.

        Returns
        -------
        self : Dataset
            Dataset with set init score.
        """
        self.init_score = init_score
        if self.handle is not None and init_score is not None:
            init_score = list_to_1d_numpy(init_score, np.float64, name='init_score')
            self.set_field('init_score', init_score)
        return self