pubsub4.py

from pyxll import RTD
import pubsub

class SubscriberRTD(RTD):

    def __init__(self, topic):
        super().__init__(value="Waiting...")
        self.__topic = topic

    def connect(self):
        pubsub.subscribe(self.__topic, self.__callback)

    def disconnect(self):
        pubsub.unsubscribe(self.__topic, self.__callback)

    def __callback(self, value):
        self.value = value