Deprecation of locale.getdefaultlocale breaks POSIX compatibility on Windows platform

[Wedge009]

Bug report

Bug description:

Follow-up to #90817.

In summary, without getdetfaultlocale, tools that rely on POSIX locales cannot reliably get the same information from getlocale or setlocale on Windows.

For example, Linux will return something like 'en_AU'. But on Windows, getlocale will return something like 'English_Australia'.

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

Windows, Linux

Linked PRs

• gh-130796: Undeprecate locale.getdefaultlocale() #143069

[picnixz]

I'm afraid that this issue is too late because the ship has already sailed. I don't remember well which alternatives there are for that kind of issue so I'll tag @vstinner who was responsible for the original patch. However, I doubt that we would reinstate locale.getdefaultlocale (or we would do something else).

EDIT: Actually it seems to only be deprecated and planned for removal in 3.15: #111187.

[Wedge009]

I don't think I - or others - was asking for a reinstatement, just a viable alternative for the cases where POSIX locales are expected for use with other tools such as gettext.

And yes, removal is planned for 3.15, hence the discussion now. As noted in wesnoth/wesnoth#9972 (comment), it's difficult to know how to work around the removal of getdefaultlocale when we don't know what future plans are - if any - for any replacement functionality.

[vstinner]

On my Windows 11 VM, getlocale() returns a "POSIX" locale as expected:

vstinner@WIN C:\victor\python\main>python
Python 3.14.0a5+ (heads/pr/130452-dirty:6a5dc1a8ba6, Feb 26 2025, 17:30:51) [MSC v.1943 32 bit (Intel)] on win32
>>> import locale
>>> locale.getlocale()
('fr_FR', 'cp1252')
>>> locale.setlocale(locale.LC_CTYPE, None)
'French_France.1252'

Can you please elaborate your issue? What are the results of locale.getlocale() and locale.setlocale(locale.LC_CTYPE, None)?

[Wedge009]

It's as I described above and in #90817 (comment).

Python 3.13.2 (tags/v3.13.2:4f8bb39, Feb  4 2025, 15:23:48) [MSC v.1942 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license()" for more information.
import locale
locale.getlocale()
('English_Australia', '1252')
locale.setlocale(locale.LC_CTYPE)
'English_Australia.1252'
locale.getdefaultlocale()

Warning (from warnings module):
  File "<pyshell#3>", line 1
DeprecationWarning: 'locale.getdefaultlocale' is deprecated and slated for removal in Python 3.15. Use setlocale(), getencoding() and getlocale() instead.
('en_AU', 'cp1252')

@shineworld reported something similar in #90817 (comment)

@Elvish-Hunter reports the same in wesnoth/wesnoth#9972 (comment)

[2trvl]

The reason why POSIX compatibility breaks is this:

The windows_locale dictionary is only used by the locale.getdefaultlocale() function and this function is deprecated: it will be removed in Python 3.15.

Windows 22H2, Python 3.13.1:

>>> locale.setlocale(locale.LC_CTYPE)
'English_United States.1252'

>>> locale.getlocale()
('English_United States', '1252')

>>> locale.getdefaultlocale()
('en_US', 'cp1252')

[2trvl]

I would like to know how can I find out the system locale for LC_TIME without using defaultlocale?

>>> locale.getdefaultlocale(["LC_TIME"])
('ru_RU', 'UTF-8')

>>> locale.setlocale(locale.LC_TIME)
'C'

>>> locale.getlocale(locale.LC_TIME)
(None, None)

Apparently I have no other option than to change the interpreter locale:

>>> locale.setlocale(locale.LC_TIME, "")
'ru_RU.UTF-8'

>>> locale.getlocale(locale.LC_TIME)
('ru_RU', 'UTF-8')

It is generally a bad idea to call setlocale() in some library routine, since as a side effect it affects the entire program. Saving and restoring it is almost as bad: it is expensive and affects other threads that happen to run before the settings have been restored.

I see that the original reason for removal is the use of non-ASCII characters in locale. Do you think this is a common case?

If fixing the problem is difficult or impossible, perhaps it is worth introducing a similar function called getpreferredlocale?