code: def shadowRegisterDeltaCallback(self, srcCallback):
          
          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)
docs: **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