[Python-Dev] PEP 538: Coercing the legacy C locale to a UTF-8 based locale

[INADA Naoki]

>>> On platforms where they would have no effect (e.g. Mac OS X, iOS, Android,
>>> Windows) these preprocessor variables would always be undefined.
>>
>> Why ``--with[out]-c-locale-coercion`` have no effect on macOS, iOS and Android?
>
> On these three, we know the system encoding is UTF-8, so we never
> interpreted the C locale as meaning "ascii" in the first place.
>
>> On Android, locale coercion fixes readline.  Do you mean locale
>> coercion happen always
>> regardless this configuration option?
>
> Right, the change for Android is that we switch to calling
> 'setlocale(LC_ALL, "C.UTF-8")' during interpreter startup instead of
> 'setlocale(LC_ALL, "")'. That change is guarded by "#ifdef
> __ANDROID__", rather than either of the new conditionals.
>
>> On macOS, ``LC_ALL=C python`` doesn't make Python's stdio to
>> ``ascii:surrogateescape``?
>
> Similar to Android, CPython itself is hardcoded to assume UTF-8 on Mac
> OS X, since that's a platform API guarantee that users can't change.
>
>> Even so, locale coercion may fix libraries like readline, curses.
>> While C locale is less common on macOS, I don't understand any
>> reason to disable it on macOS.
>
> My understanding is that other libraries and applications also
> automatically use UTF-8 for system interfaces on Mac OS X and iOS. It
> could be that that understanding is wrong, and locale coercion would
> provide a benefit there as well.
>
> (Checking the draft implementation, it turns out I haven't actually
> implemented the configure logic to make those config settings platform
> dependent yet - they're currently only undefined on Windows by
> default, since that doesn't use the autotools based build system)
>

I tried Python 3.6 on macOS 10.11 El Capitan.

  $ LANG=C python3 -c 'import locale; print(locale.getpreferredencoding())'
  US-ASCII

And interactive shell (which uses readline by default) doesn't accept non-ASCII
input anymore.
https://www.dropbox.com/s/otshuzhnw7a71n5/macos-c-locale-readline.gif?dl=0

I think many problems with C locale are same on macOS too.
So I don't think no special casing is required on macOS.

Regards,