Stefan, I thought about this at the time. But the attributes represent objects from UPnP which have those CamelCase names. I thought that having CamelCase here might be appropriate. I'm happy of course to change them, but what naming convention would you prefer? self.zone_group_topology, or something like self.zone_group_topology_service ?  I prefer the first because the second does not add much and will be a lot of typing/problems with line wraps!