def _key_on_columns(key_on, columns):
        """
        :param key_on: str of column
        :param columns: list of str of columns
        :return: list of str with the key_on in the front of the list
        """
        if key_on is not None:
            if key_on in columns:
                columns.remove(key_on)
            columns = [key_on] + columns
        return columns
:param key_on: str of column
        :param columns: list of str of columns
        :return: list of str with the key_on in the front of the list