Serhiy: "I was not sure about documenting this change in Misc/NEWS, but I think that it is not worth to mention it in What's New. This is very minor change. It's effect on any real code is negligible. I have pushed it only because it is trivial, unlikely has a negative effect, and there is a hope that the accumulated effect of several similar minor optimizations can be noticeable." I documented other similar optimizations which probably have a negligible effect. I also expect a visible effect when other optimizations are accumulated. https://docs.python.org/dev/whatsnew/3.6.html#optimizations It also a deliberate choice to document optimization. It's to communicate on the fact that we *are working* on performance. It looks like users are happy to see work done on this area: https://twitter.com/TalkPython/status/720704770198126594/photo/1 The drawback is maybe that users may have too high expectations on these optimizations.