code: def add_sink(self, sink):
          
          if sink is not None:
              self.sinks.add(sink)
              if hasattr(sink, 'start'):
                  sink.start()
docs: Add a vehicle data sink to the instance. ``sink`` should be a
          sub-class of ``DataSink`` or at least have a ``receive(message,
          **kwargs)`` method.
  
          The sink will be started if it is startable. (i.e. it has a ``start()``
          method).