code: def get_lib_and_tag_name(tag):
      
      if '.' not in tag:
          raise ValueError('Tag string must be in the format "tag_lib.tag_name"')
      lib = tag.rpartition('.')[0]
      tag_name = tag.rpartition('.')[-1]
      return lib, tag_name
docs: Takes a tag string and returns the tag library and tag name. For example,
      "app_tags.tag_name" is returned as "app_tags", "tag_name" and
      "app_tags.sub.tag_name" is returned as "app_tags.sub", "tag_name"