Set weight of each instance.

        Parameters
        ----------
        weight : list, numpy 1-D array, pandas Series or None
            Weight to be set for each data point.

        Returns
        -------
        self : Dataset
            Dataset with set weight.

def set_weight(self, weight):
        """Set weight of each instance.

        Parameters
        ----------
        weight : list, numpy 1-D array, pandas Series or None
            Weight to be set for each data point.

        Returns
        -------
        self : Dataset
            Dataset with set weight.
        """
        if weight is not None and np.all(weight == 1):
            weight = None
        self.weight = weight
        if self.handle is not None and weight is not None:
            weight = list_to_1d_numpy(weight, name='weight')
            self.set_field('weight', weight)
        return self