code: def _list_keys(self):
          
          req = self.request(self.uri + '/keys')
          keys = req.get().json()
          if keys:
              self._keys = {}
              for key in keys:
                  self._keys[key['id']] = Key(key, self)
          else:
              self._keys = {}
docs: Retrieves a list of all added Keys and populates the
          self._keys dict with Key instances
  
          :returns: A list of Keys instances