Some folks have asked about benchmarks. I don't know about iterdir() vs listdir() -- I kind of suspect the speed gains there wouldn't be big. 

However, the reason I'm keen on iterdir_stat() is that I'm seeing it speed up os.walk() by a factor of 10 in my recent tests (note that I've made local mods, so these results aren't reproducible for others yet). This is doing a walk on a dir tree with 7800 files and 155 dirs:

Using fast _betterwalk
Priming the system's cache...
Benchmarking walks on C:\Work\betterwalk\benchtree, repeat 1/3...
Benchmarking walks on C:\Work\betterwalk\benchtree, repeat 2/3...
Benchmarking walks on C:\Work\betterwalk\benchtree, repeat 3/3...
os.walk took 0.178s, BetterWalk took 0.017s -- 10.5x as fast

Sometimes Windows will go into this "I'm really caching stat results good" mode -- I don't know what heuristic determines this -- and then I'm seeing a 40x speed increase. And no, you didn't read that wrong. :-)

Sorry, I'm getting carried away. This bug is really more about iterdir. But seeing Martin suggested the stat/d_type info...