Get the feature penalty of the Dataset.

        Returns
        -------
        feature_penalty : numpy array or None
            Feature penalty for each feature in the Dataset.

def get_feature_penalty(self):
        """Get the feature penalty of the Dataset.

        Returns
        -------
        feature_penalty : numpy array or None
            Feature penalty for each feature in the Dataset.
        """
        if self.feature_penalty is None:
            self.feature_penalty = self.get_field('feature_penalty')
        return self.feature_penalty