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