I would appreciate it if you would please revert this patch.  

We need to search for a solution that isn't as fine grained (i.e. not doing increments, decrements, and tests on every single call to iter_next).  Ideally, the checks can be confined to the iterator constructor and to dealloc.  Or you could try to create some general purpose stack overflow protection that periodically makes sure there is enough stack remaining for C Python to function correctly.