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gh-151316: Prefer UTF-8 for the en_IN locale alias #155549

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gh-151316: Prefer UTF-8 for the en_IN locale alias #155549

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7 changes: 6 additions & 1 deletion Lib/locale.py
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Original file line number Diff line number Diff line change
Expand Up @@ -921,6 +921,11 @@ def getpreferredencoding(do_setlocale=True):
#
# removed 'el_gr@euro'
# removed 'uz_uz@cyrillic'
#
# gh-151316:
# Prefer UTF-8 for en_IN. X11 locale.alias maps en_IN to ISO8859-1 and that
# entry overrides glibc's en_IN/UTF-8 during makelocalealias regeneration,
# so hardcode the modern codeset (mirroring the c.utf8 carve-out).

locale_alias = {
'a3': 'az_AZ.KOI8-C',
Expand Down Expand Up @@ -1066,7 +1071,7 @@ def getpreferredencoding(do_setlocale=True):
'en_hk': 'en_HK.ISO8859-1',
'en_ie': 'en_IE.ISO8859-1',
'en_il': 'en_IL.ISO8859-1',
'en_in': 'en_IN.ISO8859-1',
'en_in': 'en_IN.UTF-8',
'en_ng': 'en_NG.UTF-8',
'en_nz': 'en_NZ.ISO8859-1',
'en_ph': 'en_PH.ISO8859-1',
Expand Down
39 changes: 39 additions & 0 deletions Lib/test/test_locale.py
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Expand Up @@ -417,6 +417,13 @@ def test_english(self):
self.check('english', 'en_EN.ISO8859-1')
self.check('english_uk.ascii', 'en_GB.ISO8859-1')

def test_en_in_utf8(self):
# gh-151316: en_IN is UTF-8 on modern glibc; do not invent ISO8859-1.
self.check('en_IN', 'en_IN.UTF-8')
self.check('en_in', 'en_IN.UTF-8')
self.assertEqual(locale._parse_localename('en_IN'), ('en_IN', 'UTF-8'))
self.assertEqual(locale._parse_localename('en_in'), ('en_IN', 'UTF-8'))

def test_hyphenated_encoding(self):
self.check('az_AZ.iso88599e', 'az_AZ.ISO8859-9E')
self.check('az_AZ.ISO8859-9E', 'az_AZ.ISO8859-9E')
Expand Down Expand Up @@ -642,6 +649,38 @@ def test_getlocale_with_modifier(self, localename, localetuple):
self.assertEqual(locale.getlocale(locale.LC_CTYPE), localetuple)


class TestEnINLocale(unittest.TestCase):
"""gh-151316: en_IN must round-trip without inventing ISO8859-1."""

def setUp(self):
self.oldlocale = locale.setlocale(locale.LC_CTYPE)
self.addCleanup(locale.setlocale, locale.LC_CTYPE, self.oldlocale)

def test_getlocale_setlocale_roundtrip(self):
try:
locale.setlocale(locale.LC_CTYPE, 'en_IN')
except locale.Error as exc:
self.skipTest(str(exc))
loc = locale.getlocale(locale.LC_CTYPE)
self.assertEqual(loc[0], 'en_IN')
self.assertNotEqual(loc[1], 'ISO8859-1')
locale.setlocale(locale.LC_CTYPE, loc)
self.assertEqual(locale.getlocale(locale.LC_CTYPE), loc)

def test_setlocale_from_getlocale_tuple(self):
# Reproduces the issue report: setlocale(LC_*, getlocale()).

@picnixz picnixz Aug 11, 2026

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This is irrelevant as a comment.

try:
locale.setlocale(locale.LC_CTYPE, 'en_IN.UTF-8')
except locale.Error:
try:
locale.setlocale(locale.LC_CTYPE, 'en_IN')
except locale.Error as exc:
self.skipTest(str(exc))
loc = locale.getlocale(locale.LC_CTYPE)
locale.setlocale(locale.LC_CTYPE, loc)
self.assertEqual(locale.getlocale(locale.LC_CTYPE)[0], 'en_IN')


class TestMiscellaneous(unittest.TestCase):
def test_defaults_UTF8(self):
# Issue #18378: on (at least) macOS setting LC_CTYPE to "UTF-8" is
Expand Down
4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Library/2026-08-11-09-47-40.gh-issue-151316.M7ANwQ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
:mod:`locale` now maps the ``en_IN`` locale alias to ``en_IN.UTF-8``
instead of the obsolete X11 ``ISO8859-1`` codeset. This restores
``setlocale(getlocale())`` round-trips on modern glibc systems where
``en_IN`` is UTF-8-only.
3 changes: 3 additions & 0 deletions Tools/i18n/makelocalealias.py
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Expand Up @@ -154,6 +154,9 @@ def check(data):
# Hardcode 'c.utf8' -> 'C.UTF-8' because 'en_US.UTF-8' does not exist
# on all platforms.
data['c.utf8'] = 'C.UTF-8'
# Hardcode 'en_in' -> 'en_IN.UTF-8'. X11 locale.alias still maps en_IN to
# ISO8859-1 and would otherwise override glibc's en_IN/UTF-8 (gh-151316).
data['en_in'] = 'en_IN.UTF-8'
while True:
# Repeat optimization while the size is decreased.
n = len(data)
Expand Down
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