> So -u does do 2/3 of what my windows_binary() does :)  Should I switch
> my test case to use stderr to demonstrate that it doesn't help with
> that?

Well, judging by the history of this code, selectively putting -u in
binary mode may be justified by the fact that Python 2 relied on the C
runtime's stdio FILE pointers, and therefore on the C runtime's own
newline translation. I would say that Python 3 should put all stdio fds
in binary mode, regardless of the -u switch.