code: def on_service_departure(self, svc_ref):
          
          with self._lock:
              try:
                  # Get the service instance
                  service = self.services.pop(svc_ref)
              except KeyError:
                  # Not a known service reference: ignore
                  pass
              else:
                  # Clean the instance values
                  self._future_value.remove(service)
  
                  # Nullify the value if needed
                  if not self._future_value:
                      self._future_value = None
  
                  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