docs: def notify(self, state, notifications):
          '''
          Call this to schedule sending partner notification.
          '''
  
          def do_append(desc, notifications):
              for notification in notifications:
                  if not isinstance(notification, PendingNotification):
                      raise ValueError("Expected notify() params to be a list "
                                       "of PendingNotification instance, got %r."
                                       % notification)
                  key = str(notification.recipient.key)
                  if key not in desc.pending_notifications:
                      desc.pending_notifications[key] = list()
                  desc.pending_notifications[key].append(notification)
  
          return state.agent.update_descriptor(do_append, notifications)