> Results without the patch:
>  ./python.exe weakref_bench.py
> 0.804216861725
> 
> Results with the patch:
> $ ./python.exe weakref_bench.py
> 0.813000202179

Thanks for the numbers, I see my worries were unfounded.

> About the test_weak_*_dict_flushed_dead_items_when_iters_go_out:
> 
> If a weakref dict keeps its weak reference alive, it's not an 
> implementation detail, it's a bug. The whole point of using such dicts 
> is to not keep keys or values alive when they go out.

I was talking about doing `self.assertEqual(len(d), self.COUNT)` before
deleting the iterators.