>I don't believe it. I don't see what's magical about being called by the
>gc. Again, a Py_DECREF in tp_dealloc can invoke arbitrary Python code.

Look again.  gcmodule specifically takes any objects reachable from ob_clear and sees if any of them have side effects when Py_DECREF'd.  If any object has a finalizer, the entire cycle is put in gc.garbage.

gcmodule is trickier than you might think.  I've spent quite a time with it.

Anyway, I've put the issue to python-dev, let's see if they have some autorative insight on the matter.