def _get_mvar(cls, df, column, windows):
        """ get moving variance

        :param df: data
        :param column: column to calculate
        :param windows: collection of window of moving variance
        :return: None
        """
        window = cls.get_only_one_positive_int(windows)
        column_name = '{}_{}_mvar'.format(column, window)
        df[column_name] = df[column].rolling(
            min_periods=1, window=window, center=False).var()
get moving variance

        :param df: data
        :param column: column to calculate
        :param windows: collection of window of moving variance
        :return: None