I do not want to make type-checker a part of CPython, I just what options that will allow to run python with first some type-checker ... For example, you would be able to set default python module for type-checking and if there is not module set for type checking, verify if `mypy` installed and if installed run it first ... The issue with separate running type-checker first and then script is that it is separate commands and failing run script is console dependent: in bash `set -e` and etc. in other consoles Better to have terminal agnostic option that will allow to do the same thing ... Also I think that maybe it would be also good to have `*.ty` (Typed pYthon) that would mean if python understand extension `ty` then it will run default type checker if it is available and then script ... Anyway as you can see there is obvious reason to add CPython flag and it is not enforce to CPython somehow to integrate type checker in its source code ...