code: def tags_check_convert(cls, tags):
          
          # single string check comes first since string is also a Sequence
          if isinstance(tags, string_types):
              return [cls.__tag_check_convert(tags)]
          elif isinstance(tags, Sequence):
              if not tags:
                  raise ValueError("Tag list is empty")
              return [cls.__tag_check_convert(tag) for tag in tags]
          else:
              raise ValueError("tags must be a single string or list of sequence of strings")
docs: Accept one tag as string or multiple tags in list of strings.
          Returns list (with tags in unicode form) or raises ValueError