code: def on_service_departure(self, svc_ref):
          
          with self._lock:
              if svc_ref in self.services:
                  # Get the service instance
                  service = self.services.pop(svc_ref)
  
                  # Get the key property
                  prop_value = svc_ref.get_property(self._key)
  
                  # Remove the injected service
                  self.__remove_service(prop_value, service)
  
                  self._ipopo_instance.unbind(self, service, svc_ref)
                  return True
  
              return None
docs: Called when a service has been unregistered from the framework
  
          :param svc_ref: A service reference
          :return: A tuple (service, reference) if the service has been lost,
                   else None