**Description**

        Listen on delta topics for this device shadow by subscribing to delta topics. Whenever there 
        is a difference between the desired and reported state, the registered callback will be called 
        and the delta payload will be available in the callback.

        **Syntax**

        .. code:: python

          # Listen on delta topics for BotShadow
          BotShadow.shadowRegisterDeltaCallback(customCallback)

        **Parameters**

        *srcCallback* - Function to be called when the response for this shadow request comes back. Should 
        be in form :code:`customCallback(payload, responseStatus, token)`, where :code:`payload` is the 
        JSON document returned, :code:`responseStatus` indicates whether the request has been accepted, 
        rejected or is a delta message, :code:`token` is the token used for tracing in this request.

        **Returns**

        None

def shadowRegisterDeltaCallback(self, srcCallback):
        """
        **Description**

        Listen on delta topics for this device shadow by subscribing to delta topics. Whenever there 
        is a difference between the desired and reported state, the registered callback will be called 
        and the delta payload will be available in the callback.

        **Syntax**

        .. code:: python

          # Listen on delta topics for BotShadow
          BotShadow.shadowRegisterDeltaCallback(customCallback)

        **Parameters**

        *srcCallback* - Function to be called when the response for this shadow request comes back. Should 
        be in form :code:`customCallback(payload, responseStatus, token)`, where :code:`payload` is the 
        JSON document returned, :code:`responseStatus` indicates whether the request has been accepted, 
        rejected or is a delta message, :code:`token` is the token used for tracing in this request.

        **Returns**

        None

        """
        with self._dataStructureLock:
            # Update callback data structure
            self._shadowSubscribeCallbackTable["delta"] = srcCallback
        # One subscription
        self._shadowManagerHandler.basicShadowSubscribe(self._shadowName, "delta", self.generalCallback)
        self._logger.info("Subscribed to delta topic for deviceShadow: " + self._shadowName)