code: def on_service_departure(self, svc_ref):
          
          with self._lock:
              if svc_ref is self.reference:
                  # Forget about the service
                  self._value.unset_service()
  
                  # Clear the reference
                  self.reference = None
  
                  # Look for a replacement
                  self._pending_ref = self._context.get_service_reference(
                      self.requirement.specification, self.requirement.filter
                  )
  
                  if self._pending_ref is None:
                      # No replacement found yet, wait a little
                      self.__still_valid = True
                      self.__timer_args = (self._value, svc_ref)
                      self.__timer = threading.Timer(
                          self.__timeout, self.__unbind_call, (False,)
                      )
                      self.__timer.start()
  
                  else:
                      # Notify iPOPO immediately
                      self._ipopo_instance.unbind(self, self._value, svc_ref)
                  return True
  
              return None
docs: Called when a service has been unregistered from the framework
  
          :param svc_ref: A service reference