code: def list_clients(self, instance=None):
          
          # Server does not do pagination on listings of this resource.
          # Return an iterator anyway for similarity with other API methods
          url = '/clients'
          if instance:
              url = '/instances/{}/clients'.format(instance)
          response = self.get_proto(path=url)
          message = rest_pb2.ListClientsResponse()
          message.ParseFromString(response.content)
          clients = getattr(message, 'client')
          return iter([Client(client) for client in clients])
docs: Lists the clients.
  
          :param Optional[str] instance: A Yamcs instance name.
          :rtype: ~collections.Iterable[yamcs.model.Client]