code: def _ListTags(self):
      
      all_tags = []
      self._cursor.execute('SELECT DISTINCT tag FROM log2timeline')
  
      # This cleans up the messy SQL return.
      tag_row = self._cursor.fetchone()
      while tag_row:
        tag_string = tag_row[0]
        if tag_string:
          tags = tag_string.split(',')
          for tag in tags:
            if tag not in all_tags:
              all_tags.append(tag)
        tag_row = self._cursor.fetchone()
      # TODO: make this method an iterator.
      return all_tags
docs: Query database for unique tag types.