Thanks Steven, this is great!
so -- when all this started, I think one of the use cases was to clean up this really common idiom:
self.an_arg = the_default if an_arg is None else an_arg
so would that be:
self.an_arg = the_default ?? an_arg
That would be nice.
Though the fact that I'm still not sure if that's correct makes me think this is not so intuitive!