code: def get_wf(self,token_id):
            
          wf_node = self.idx.get(token_id)
          if wf_node is not None:
              return Cwf(node=wf_node,type=self.type)
          else:
              for wf_node in self.__get_wf_nodes():
                  if self.type == 'NAF': label_id = 'id'
                  elif self.type == 'KAF': label_id = 'wid'
                  if wf_node.get(label_id) == token_id:
                      return Cwf(node=wf_node, type=self.type)                                                                
              return None
docs: Returns the token object for the given token identifier
          @type token_id: string
          @param token_id: the token identifier
          @rtype: L{Cwf}
          @return: the token object