code: def list_id(self):
          
          list_id = getattr(self, '_list_id', None)
  
          if list_id is None:
              for l in self.api.lists.all()['lists']:
                  if l['name'] == self.list_name:
                      self._list_id = l['id']
  
              if not getattr(self, '_list_id', None):
                  self._list_id = self.api.lists.create(
                      label=self.list_label, name=self.list_name,
                      method='POST')['list_id']
  
          return self._list_id
docs: Get or create the list id.