code: def list(self, **kwargs):
          
          self.custom_category = kwargs.get('category', 'all')
          try:
              result = super(Resource, self).list(**kwargs)
          except exc.NotFound as e:
              categories = map(
                  lambda category: category['slug'],
                  client.get('/settings/').json()['results']
              )
              e.message = '%s is not a valid category.  Choose from [%s]' % (
                  kwargs['category'],
                  ', '.join(categories)
              )
              raise e
          finally:
              self.custom_category = None
          return {
              'results': [{'id': k, 'value': v} for k, v in result.items()]
          }
docs: Return a list of objects.
  
          =====API DOCS=====
          Retrieve a list of Tower settings.
  
          :param category: The category slug in which to look up indevidual settings.
          :type category: str
          :param `**kwargs`: Keyword arguments list of available fields used for searching resource objects.
          :returns: A JSON object containing details of all resource objects returned by Tower backend.
          :rtype: dict
  
          =====API DOCS=====