I think you're on the right track with this by looking at the Python module. What I want to try here is something along the lines of defining the type originally in Python and relying on the Python module's Class wrapper type, then potentially defining methods in Chapel as much as possible and calling over into the Python type for only the more basic functionality. But I'm not sure if that'd allow you to call those methods from Python, or even what the performance would look like from doing so, as it might still require a custom TypeConverter to accomplish that or even some feature requests for things we haven't implemented yet.

I'm hoping Jade will chime in on this thread, they may have some better ideas than I do. In the meanwhile, I'll muse on the structure of this and play with some things locally.