code: def invitation_backend(backend=None, namespace=None):
      # type: (Optional[Text], Optional[Text]) -> BaseBackend
      
      backend = backend or ORGS_INVITATION_BACKEND
      class_module, class_name = backend.rsplit(".", 1)
      mod = import_module(class_module)
      return getattr(mod, class_name)(namespace=namespace)
docs: Returns a specified invitation backend
  
      Args:
          backend: dotted path to the invitation backend class
          namespace: URL namespace to use
  
      Returns:
          an instance of an InvitationBackend