Get the monotone constraints of the Dataset.

        Returns
        -------
        monotone_constraints : numpy array or None
            Monotone constraints: -1, 0 or 1, for each feature in the Dataset.

def get_monotone_constraints(self):
        """Get the monotone constraints of the Dataset.

        Returns
        -------
        monotone_constraints : numpy array or None
            Monotone constraints: -1, 0 or 1, for each feature in the Dataset.
        """
        if self.monotone_constraints is None:
            self.monotone_constraints = self.get_field('monotone_constraints')
        return self.monotone_constraints