add a tag or tags to a Feed

def add_tags(self, tags):
        """ add a tag or tags to a Feed """

        if isinstance(tags, (str, unicode)):
            tags = [tags]

        objs = object_session(self)
        tmps = [FeedTag(tag=t, feed=self) for t in tags]
        objs.add_all(tmps)
        objs.commit()