That is true. And we can't change Python 2. I still have this idea in my head that *most* cases where %s is used in Python 2 will break in Python 3 under the PEP's rules, but perhaps they are not the majority of situations where the context is manipulating bytes. And I suppose that *very* few internet protocols are designed to accept either an integer or the literal string None, so that use case (which I brought up) isn't very realistic -- in fact it may be better to raise an exception rather than sending a protocol violation.

So, I think you have changed my mind. I still like the idea of promoting %b in pure Python 3 code to emphasize that it really behaves very differently from %s; but I now have peace with %s as an alias. (It might also benefit cases where somehow there's a symmetry in some Python 3 code between bytes and str.)