def _addTags(service, user, item, tagList):
    i = TagItem.get_by(type_id=service, item_id=item)
    if not i:
        i = TagItem(type_id=service, item_id=item)

    if not isinstance(tagList, list) or len(tagList) == 0:
       raise TypeError, "Need a list of tags"

    for t in i.tags:
       if t.name not in set(tagList):
          t = Tag.get_by(name=tag)
          if not t:
             t = Tag(name=tag)
          i.tags.append(t)