code: def on_service_modify(self, svc_ref, old_properties):
          
          with self._lock:
              try:
                  # Look for the service
                  service = self.services[svc_ref]
              except KeyError:
                  # A previously registered service now matches our filter
                  return self.on_service_arrival(svc_ref)
              else:
                  # Notify the property modification
                  self._ipopo_instance.update(
                      self, service, svc_ref, old_properties
                  )
  
              return None
docs: Called when a service has been modified in the framework
  
          :param svc_ref: A service reference
          :param old_properties: Previous properties values
          :return: A tuple (added, (service, reference)) if the dependency has
                   been changed, else None