Not obvious that locale.LC_MESSAGES may not exist sometimes (e.g. on Windows)

[richardmines91]

BPO	44387
Nosy	@jdevries3133
Files	lc_messages_not_exist.png: Proof that locale.LC_MESSAGES may not exist in Python

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-06-10.23:27:24.102>
labels = ['3.7', '3.8', '3.9', '3.10', '3.11', 'type-feature', 'docs']
title = 'Not obvious that locale.LC_MESSAGES may not exist sometimes (e.g. on Windows)'
updated_at = <Date 2021-06-11.07:21:26.140>
user = 'https://bugs.python.org/richardmines91'

bugs.python.org fields:

activity = <Date 2021-06-11.07:21:26.140>
actor = 'richardmines91'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2021-06-10.23:27:24.102>
creator = 'richardmines91'
dependencies = []
files = ['50102']
hgrepos = []
issue_num = 44387
keywords = []
message_count = 4.0
messages = ['395588', '395590', '395591', '395607']
nosy_count = 3.0
nosy_names = ['docs@python', 'jack__d', 'richardmines91']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44387'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

[richardmines91]

Documentation page:
https://docs.python.org/3/library/locale.html#locale.LC_MESSAGES

Code comment saying that locale.LC_MESSAGES doesn't exist sometimes:

cpython/Lib/locale.py

Lines 25 to 26 in 62f1d2b

	# Yuck: LC_MESSAGES is non-standard: can't tell whether it exists before
	# trying the import. So __all__ is also fiddled at the end of the file.

Code fragment showing that locale.LC_MESSAGES can be non-existent:

cpython/Lib/locale.py

Lines 1747 to 1752 in 62f1d2b

	try:
	LC_MESSAGES
	except NameError:
	pass
	else:
	__all__.append("LC_MESSAGES")

Reading documentation it's not obvious that locale.LC_MESSAGES may not exist (e.g. Windows - Microsoft Store - Python 3.8)

[jdevries3133]

Could it be that _locale throws an ImportError whenever LC_MESSAGES doesn't exist? Then, there are fall-backs defined here:

cpython/Lib/locale.py

Lines 45 to 85 in 62f1d2b

	try:
	from _locale import *
	except ImportError:
	# Locale emulation
	CHAR_MAX = 127
	LC_ALL = 6
	LC_COLLATE = 3
	LC_CTYPE = 0
	LC_MESSAGES = 5
	LC_MONETARY = 4
	LC_NUMERIC = 1
	LC_TIME = 2
	Error = ValueError
	def localeconv():
	""" localeconv() -> dict.
	Returns numeric and monetary locale-specific parameters.
	"""
	# 'C' locale default values
	return {'grouping': [127],
	'currency_symbol': '',
	'n_sign_posn': 127,
	'p_cs_precedes': 127,
	'n_cs_precedes': 127,
	'mon_grouping': [],
	'n_sep_by_space': 127,
	'decimal_point': '.',
	'negative_sign': '',
	'positive_sign': '',
	'p_sep_by_space': 127,
	'int_curr_symbol': '',
	'p_sign_posn': 127,
	'thousands_sep': '',
	'mon_thousands_sep': '',
	'frac_digits': 127,
	'mon_decimal_point': '',
	'int_frac_digits': 127}

[jdevries3133]

Follow-up: nope! My hypothesis was incorrect. This is all that _localemodule.c has to say about LC_MESSAGES:

#ifdef LC_MESSAGES
    ADD_INT(module, LC_MESSAGES);
#endif /* LC_MESSAGES */

[richardmines91]

If you need a proof that it is possible that locale.LC_MESSAGES doesn't exist, I've attached a screenshot. Even more I'm showing that locale.LC_TIME may be equal to 5 which is a placeholder for locale.LC_MESSAGES if there is an ImportError:

cpython/Lib/locale.py

Line 57 in 62f1d2b

LC_MESSAGES = 5

OS: Windows 10 20H2
Python: 3.8.10
Exact link to get python: https://www.microsoft.com/ru-ru/p/python-38/9mssztt1n39l?activetab=pivot:overviewtab

[cdfarrow]

Duplicate of gh-100766, which was fixed on Jan 5, 2023.
I'm suggesting formatting the information as a note in this PR