It is hard to reproduce (especially the second issue) since in all cases in the stdlib a list passed to fork_exec() is just created by sorted() and doesn't have other references. But if someone is so insane that passes int-like objects with non-idempotent __int__ as file descriptors his can get a crash in debug build (or mystical bugs in release build). Added tests utilizes this, but this unlikely happens in real code.

I have found this issue during analyzing usages of PyObject_Size(), PySequence_Size() and PyMapping_Size() in issue30061.