* Mypy dependency and really bad PEP compliance * Sub-optimal runtime check decorators * Subclasses pd.DataFrame, so using e.g. .assign(...) makes the type checker think it's still the same type, but now you just violated your own schema

So I wrote my own library that solves all these issues, but it's currently company-internal. I've been meaning to push for open-sourcing it, but just haven't had the time.