[_fbpt]

Try @attr.dataclass. It uses the cleaner 3.6+ dataclass syntax, but is more flexible (supports kw-only classes).

[thedigicat]

Thank you both for your suggestions, I will consider using one of these in the next versions of the book. Python is a moving target, so I will have to update the examples.

[MrSaints]

I've recently also come across https://pydantic-docs.helpmanual.io/ which appears to be useful for enforcing simple constraints on domain entities.