I've never worked with RPython. Looking through that list it doesn't look dreadful. There are a couple of things that jump out though - you can't use kwargs in

I've never worked with RPython. Looking through that list it doesn't look dreadful. There are a couple of things that jump out though - you can't use kwargs in function definitions which is probably used quite a lot in dynamic settings. Eg in Python one might do (warning; crazy, contrived example): def create_thing(**kwargs): thing = dict(id=gen_id()) thing['other_data'] = kwargs return thing thing = create_thing(name='name', foo='bar') You could avoid it, and generally in Python you're better off being explicit about everything. But it's definitely a feature that gets used a fair amount, especially in libraries where you don't explicitly know what the api call takes concerning user data. An easy (more explicit) workaround would be: def create_thing(other_data=None): thing = dict(id=gen_id()) thing['other_data'] = other_data or {} return thing create_thing(dict(name='name', foo='bar')) It's just a little more work for the calling code.