Some more discussion in this thread https://mail.python.org/archives/list/typing-sig@python.org/thread/QSCT2N4RFPRQN2U7NIX6VCNVNDHGO22U/ https://mail.python.or

Some more discussion in this thread https://mail.python.org/archives/list/typing-sig@python.org/thread/QSCT2N4RFPRQN2U7NIX6VCNVNDHGO22U/ https://mail.python.org/archives/list/typing-sig@python.org/... I have a fork of the "adt" library that supports sealed classes. For static type checking, I'm using a fork of typpete, a SMT based type checker. It's not as user friendly as mypy or pyright, but in the longer term can be a winner because it supports user defined type constraints (aka refinement types).