Solved on SO, but an extremely educational response. I learned about mutable default argument gotcha https://stackoverflow.com/questions/1132941/least-astonishment-and-the-mutable-default-argument
And Django Modified Preorder Tree Traversal https://github.com/django-mptt/django-mptt -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/7bc04d03-76f1-4913-b44a-5e52d851c5e4%40googlegroups.com.
