FWIW, the script name appears to be relevant as well. I were going to say that I could not reproduce it as it was; this same example saved as "a.py" doesn't show the error; "w.py" does.

To the OP: Module finalization is a fragile step; this is a long standing issue and could be improved, but anyway I don't think it can be made robust enough (this is just my opinion!). I usually try to *never* reference any globals in destructors. In this case, using self.__class__ instead of Person is safer and works fine; if other globals were needed they could be passed as default argument values.