docs: def pick(self, *args):
          """
          Return a copy of the object only containing the
          whitelisted properties.
          """
          ns = self.Namespace()
          ns.result = {}
  
          def by(key, *args):
              if key in self.obj:
                  ns.result[key] = self.obj[key]
  
          _.each(self._flatten(args, True, []), by)
          return self._wrap(ns.result)