code: def _url(self):
          
          if self._api_arg:
              mypart = str(self._api_arg)
          else:
              mypart = self._name
  
          if self._parent:
              return '/'.join(filter(None, [self._parent._url, mypart]))
          else:
              return mypart
docs: Resolve the URL to this point.
  
          >>> trello = TrelloAPIV1('APIKEY')
          >>> trello.batch._url
          '1/batch'
          >>> trello.boards(board_id='BOARD_ID')._url
          '1/boards/BOARD_ID'
          >>> trello.boards(board_id='BOARD_ID')(field='FIELD')._url
          '1/boards/BOARD_ID/FIELD'
          >>> trello.boards(board_id='BOARD_ID').cards(filter='FILTER')._url
          '1/boards/BOARD_ID/cards/FILTER'