Python uses cycle breaking i.e. it chooses an object on a circular path and simply deletes it, which essentially bricks the entire connected set for reference c

Python uses cycle breaking i.e. it chooses an object on a circular path and simply deletes it, which essentially bricks the entire connected set for reference counting purposes. This means that if you ran __del__ code in this circumstance it could access references to deleted objects, i.e. use after free. __del__ is simply an unsound part of Python.