Add prefix to the label

        :param prefix:
        :param iterable:
        :return:

def make_prefix(self, prefix, iterable):
        """
        Add prefix to the label

        :param prefix:
        :param iterable:
        :return:
        """
        if not prefix:
            yield from iterable

        for key, value in iterable:
            yield f"{prefix}_{key}", value