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Description:
 A test case is failing while running `./python -m test -v test_re`.
Traceback:
$>./python -m test -v test_re
== CPython 3.7.0a0 (default, Feb 15 2017, 22:28:32) [GCC 5.4.0 20160609]
== Linux-4.4.0-62-generic-x86_64-with-debian-stretch-sid little-endian
== hash algorithm: siphash24 64bit
== cwd: /home/bigj/Jaysinh/cpython_git/cpython/build/test_python_613
== encodings: locale=UTF-8, FS=utf-8
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, ignore_environment=0, verbose=0, bytes_warning=0, quiet=0, hash_randomization=1, isolated=0)
Run tests sequentially
0:00:00 [1/1] test_re
test_re_benchmarks (test.test_re.ExternalTests)
re_tests benchmarks ... ok
test_re_tests (test.test_re.ExternalTests)
re_tests test suite ... ok
test_overlap_table (test.test_re.ImplementationTest) ... ok
test_bytes (test.test_re.PatternReprTests) ... ok
test_inline_flags (test.test_re.PatternReprTests) ... ok
test_locale (test.test_re.PatternReprTests) ... ok
test_long_pattern (test.test_re.PatternReprTests) ... ok
test_multiple_flags (test.test_re.PatternReprTests) ... ok
test_quotes (test.test_re.PatternReprTests) ... ok
test_single_flag (test.test_re.PatternReprTests) ... ok
test_unicode_flag (test.test_re.PatternReprTests) ... ok
test_unknown_flags (test.test_re.PatternReprTests) ... ok
test_without_flags (test.test_re.PatternReprTests) ... ok
test_anyall (test.test_re.ReTests) ... ok
test_ascii_and_unicode_flag (test.test_re.ReTests) ... ok
test_backref_group_name_in_exception (test.test_re.ReTests) ... ok
test_basic_re_sub (test.test_re.ReTests) ... ok
test_big_codesize (test.test_re.ReTests) ... ok
test_bigcharset (test.test_re.ReTests) ... ok
test_bug_113254 (test.test_re.ReTests) ... ok
test_bug_114660 (test.test_re.ReTests) ... ok
test_bug_117612 (test.test_re.ReTests) ... ok
test_bug_1661 (test.test_re.ReTests) ... ok
test_bug_16688 (test.test_re.ReTests) ... ok
test_bug_20998 (test.test_re.ReTests) ... ok
test_bug_2537 (test.test_re.ReTests) ... ok
test_bug_29444 (test.test_re.ReTests) ... ok
test_bug_3629 (test.test_re.ReTests) ... ok
test_bug_418626 (test.test_re.ReTests) ... ok
test_bug_448951 (test.test_re.ReTests) ... ok
test_bug_449000 (test.test_re.ReTests) ... ok
test_bug_449964 (test.test_re.ReTests) ... ok
test_bug_462270 (test.test_re.ReTests) ... ok
test_bug_527371 (test.test_re.ReTests) ... ok
test_bug_581080 (test.test_re.ReTests) ... ok
test_bug_612074 (test.test_re.ReTests) ... ok
test_bug_6509 (test.test_re.ReTests) ... ok
test_bug_6561 (test.test_re.ReTests) ... ok
test_bug_725106 (test.test_re.ReTests) ... ok
test_bug_725149 (test.test_re.ReTests) ... ok
test_bug_764548 (test.test_re.ReTests) ... ok
test_bug_817234 (test.test_re.ReTests) ... ok
test_bug_926075 (test.test_re.ReTests) ... ok
test_bug_931848 (test.test_re.ReTests) ... ok
test_bytes_str_mixing (test.test_re.ReTests) ... ok
test_category (test.test_re.ReTests) ... ok
test_character_set_errors (test.test_re.ReTests) ... ok
test_compile (test.test_re.ReTests) ... ok
test_constants (test.test_re.ReTests) ... ok
test_dealloc (test.test_re.ReTests) ... ok
test_debug_flag (test.test_re.ReTests) ... ok
test_dollar_matches_twice (test.test_re.ReTests)
$ matches the end of string, and just before the terminating ... ok
test_empty_array (test.test_re.ReTests) ... ok
test_enum (test.test_re.ReTests) ... ok
test_error (test.test_re.ReTests) ... ok
test_expand (test.test_re.ReTests) ... ok
test_finditer (test.test_re.ReTests) ... ok
test_flags (test.test_re.ReTests) ... ok
test_getattr (test.test_re.ReTests) ... ok
test_getlower (test.test_re.ReTests) ... ok
test_group (test.test_re.ReTests) ... ok
test_group_name_in_exception (test.test_re.ReTests) ... ok
test_groupdict (test.test_re.ReTests) ... ok
test_ignore_case (test.test_re.ReTests) ... ok
test_ignore_case_range (test.test_re.ReTests) ... ok
test_ignore_case_set (test.test_re.ReTests) ... ok
test_inline_flags (test.test_re.ReTests) ... ok
test_issue17998 (test.test_re.ReTests) ... ok
test_keep_buffer (test.test_re.ReTests) ... ok
test_keyword_parameters (test.test_re.ReTests) ... ok
test_large_search (test.test_re.ReTests) ... ok
test_large_subn (test.test_re.ReTests) ... ok
test_locale_caching (test.test_re.ReTests) ... skipped 'test needs en_US.iso88591 locale'
test_locale_flag (test.test_re.ReTests) ... FAIL
test_lookahead (test.test_re.ReTests) ... ok
test_lookbehind (test.test_re.ReTests) ... ok
test_match_getitem (test.test_re.ReTests) ... ok
test_match_repr (test.test_re.ReTests) ... ok
test_misc_errors (test.test_re.ReTests) ... ok
test_multiple_repeat (test.test_re.ReTests) ... ok
test_not_literal (test.test_re.ReTests) ... ok
test_nothing_to_repeat (test.test_re.ReTests) ... ok
test_other_escapes (test.test_re.ReTests) ... ok
test_pattern_compare (test.test_re.ReTests) ... ok
test_pattern_compare_bytes (test.test_re.ReTests) ... ok
test_pickling (test.test_re.ReTests) ... ok
test_qualified_re_split (test.test_re.ReTests) ... ok
test_qualified_re_sub (test.test_re.ReTests) ... ok
test_re_escape (test.test_re.ReTests) ... ok
test_re_escape_byte (test.test_re.ReTests) ... ok
test_re_escape_non_ascii (test.test_re.ReTests) ... ok
test_re_escape_non_ascii_bytes (test.test_re.ReTests) ... ok
test_re_findall (test.test_re.ReTests) ... ok
test_re_fullmatch (test.test_re.ReTests) ... ok
test_re_groupref (test.test_re.ReTests) ... ok
test_re_groupref_exists (test.test_re.ReTests) ... ok
test_re_groupref_overflow (test.test_re.ReTests) ... ok
test_re_match (test.test_re.ReTests) ... ok
test_re_split (test.test_re.ReTests) ... ok
test_re_subn (test.test_re.ReTests) ... ok
test_repeat_minmax (test.test_re.ReTests) ... ok
test_repeat_minmax_overflow (test.test_re.ReTests) ... ok
test_repeat_minmax_overflow_maxrepeat (test.test_re.ReTests) ... ok
test_scanner (test.test_re.ReTests) ... ok
test_scoped_flags (test.test_re.ReTests) ... ok
test_search_coverage (test.test_re.ReTests) ... ok
test_search_dot_unicode (test.test_re.ReTests) ... ok
test_search_star_plus (test.test_re.ReTests) ... ok
test_special_escapes (test.test_re.ReTests) ... ok
test_sre_byte_class_literals (test.test_re.ReTests) ... ok
test_sre_byte_literals (test.test_re.ReTests) ... ok
test_sre_character_class_literals (test.test_re.ReTests) ... ok
test_sre_character_literals (test.test_re.ReTests) ... ok
test_stack_overflow (test.test_re.ReTests) ... ok
test_string_boundaries (test.test_re.ReTests) ... ok
test_sub_template_numeric_escape (test.test_re.ReTests) ... ok
test_symbolic_groups (test.test_re.ReTests) ... ok
test_symbolic_refs (test.test_re.ReTests) ... ok
test_unlimited_zero_width_repeat (test.test_re.ReTests) ... ok
test_weakref (test.test_re.ReTests) ... ok
======================================================================
FAIL: test_locale_flag (test.test_re.ReTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/bigj/Jaysinh/cpython_git/cpython/Lib/test/test_re.py", line 1422, in test_locale_flag
 self.assertTrue(pat.match(bletter))
AssertionError: None is not true
----------------------------------------------------------------------
Ran 120 tests in 2.079s
FAILED (failures=1, skipped=1)
test test_re failed
test_re failed
1 test failed:
 test_re
Total duration: 2 sec
Tests result: FAILURE
Local value:
$>locale
LANG=en_IN
LANGUAGE=en_IN:en
LC_CTYPE="en_IN"
LC_NUMERIC="en_IN"
LC_TIME="en_IN"
LC_COLLATE="en_IN"
LC_MONETARY="en_IN"
LC_MESSAGES="en_IN"
LC_PAPER="en_IN"
LC_NAME="en_IN"
LC_ADDRESS="en_IN"
LC_TELEPHONE="en_IN"
LC_MEASUREMENT="en_IN"
LC_IDENTIFICATION="en_IN"
LC_ALL=
Operating system: Ubuntu 16.04 LTS(64 bit)

I'm just wondering whether the problem is just due to the locale's encoding being UTF-8. The locale support in re really only works with encodings that use 1 byte/character.

Locale encoding is ISO8859-1. This test is skipped on non 8-bit locale.
This is a problem with tests, not with the re module. I don't have a solution.

The report says "== encodings: locale=UTF-8, FS=utf-8".
It says that "test_locale_caching" was skipped, but also that "test_locale_flag" failed.

Good point. The test used locale.getlocale() and it returned returned ('en_IN', 'ISO8859-1').
Following patch makes the test using locale.getpreferredencoding(False), the same encoding as was reported at the header of test report.

> Following patch ...
Seriously? Not a GitHub pull request? ;-) (old habit?)

> Seriously? Not a GitHub pull request? ;-) (old habit?)
I'm not experienced with git, and devguide still looks not ready.

I have a few folks hitting this at the PyCon Pune sprints, so I'm going to apply Serhiy's patch :)

Looking into this at the PyCon Pune sprints, the problem appears to be arising due to the following difference in behaviour when the unqualifed `en_IN` locale is set:
$ LANG=en_IN.UTF-8 python3 -c "import locale; print(locale.getlocale(locale.LC_CTYPE), locale.getpreferredencoding(False), sep='\n')"
('en_IN', 'UTF-8')
UTF-8
$ LANG=en_IN python3 -c "import locale; print(locale.getlocale(locale.LC_CTYPE), locale.getpreferredencoding(False), sep='\n')"
('en_IN', 'ISO8859-1') 
UTF-8
re.LOCALE is presumably picking up the "UTF-8" rather than the "ISO8859-1", and hence the test is failing.

Yes, please push it Nick.

New changeset ace5c0fdd9b962e6e886c29dbcea72c53f051dc4 by GitHub in branch 'master':
bpo-29571: Use correct locale encoding in test_re (#149)
https://github.com/python/cpython/commit/ace5c0fdd9b962e6e886c29dbcea72c53f051dc4

New changeset 0683d6889bd4430599d22e12e201b8e9c45be5a2 by GitHub in branch '3.6':
[3.6] bpo-29571: Use correct locale encoding in test_re (#149) (#153)
https://github.com/python/cpython/commit/0683d6889bd4430599d22e12e201b8e9c45be5a2

New changeset 760f596b6a4b5514afe35e521621f484aef35413 by GitHub in branch '3.5':
[3.5] bpo-29571: Use correct locale encoding in test_re (#149) (#154)
https://github.com/python/cpython/commit/760f596b6a4b5514afe35e521621f484aef35413

This seems to have broken test_re on Windows, see https://ci.appveyor.com/project/python/cpython/build/3.7.0a0.1
I found this change to be the culprit via git bisect, unfortunately we didn't have any working CI on Windows (buildbots were otherwise broken) at the time this was merged.

Yep, I think we should merge https://github.com/python/cpython/pull/422 and revert ncoghlan's change.

I'm not sure this will help on Windows.

And I don't understand why my fix doesn't work on Windows.

But the test was never broken on windows.
On Sun, Mar 5, 2017, at 23:54, Serhiy Storchaka wrote:
> 
> Serhiy Storchaka added the comment:
> 
> I'm not sure this will help on Windows.
> 
> ----------
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue29571>
> _______________________________________

getpreferredencoding() takes a completely different path on windows
(returns a codepage) and isn't related to the C locale.

I'm with Serhiy on this one: if the "re" module isn't using locale.getpreferredencoding(), then there's something odd going on.
It just sounds like the disconnect on Windows is the opposite of the one we hit on Linux without Benjamin's patch, perhaps due to the UTF-8 mode changes - it wouldn't surprise me to learn that the re module is still using mbcs there instead of utf-8.

I don't see what's odd about it. re.LOCALE uses the C locale, which one
obtains from locale.getlocale(). getpreferredencoding() is not
documented to have anything to do with the C locale, and indeed on
Windows it may be completely different.

Thanks for the explanation - given that, I agree that simply reverting the attempted test-based fix and instead relying on the issue 20087 updates is the way to go.

New changeset 6a4b04cd337347d074ae0140fb13dca5bd4b11ef by Benjamin Peterson in branch '3.6':
Revert "bpo-29571: Use correct locale encoding in test_re (#149)" (#554) (#555)
https://github.com/python/cpython/commit/6a4b04cd337347d074ae0140fb13dca5bd4b11ef

New changeset 312f7dfb7c669fcfc43020951b7f8ff521200ad7 by Benjamin Peterson in branch '3.5':
Revert "bpo-29571: Use correct locale encoding in test_re (#149)" (#554) (#556)
https://github.com/python/cpython/commit/312f7dfb7c669fcfc43020951b7f8ff521200ad7

New changeset 21a74312f2d1ddee71fade709af49d078085ec30 by Benjamin Peterson in branch 'master':
Revert "bpo-29571: Use correct locale encoding in test_re (#149)" (#554)
https://github.com/python/cpython/commit/21a74312f2d1ddee71fade709af49d078085ec30

Hmm, even though we reverted the original test_re based change, and the initial attempted fix for bpo-20087 was also reverted, I'm still not currently seeing the failure for:
 LANG=en_IN.utf8 ./python -m test -v test_re
I do have the locale installed, so it's not a result of falling back to the C locale and that getting coerced to C.UTF-8:
 $ LANG=en_IN.utf8 locale -k currency_symbol
 currency_symbol="₹"
Jaysinh, are you still seeing this test failure on a fresh checkout?

Hmm, this actually works for me on Fedora 27 even if I go back to 1b3d88eb33085e90af729c4c2f78b5ba1b942b1e, the commit just before the initially merged (and subsequently reverted) test change above.
Unassigning, since I can't readily reproduce it myself.

Hello Nick,
 At the devsprints of Pycon India 2017, a few participants were facing this bug. They all were from the Ubuntu land. I have switched to Gentoo distro. I am not facing this bug, but let me confirm from any Ubuntu user. Thanks

I've also added Matthias and Barry to the cc list, in case this does turn out to be a Debian or Ubuntu specific quirk.
Restating the problem, the issue is that test_locale_flag in test_re may fail for at least the en_IN locale, and we're not sure yet whether that's a test bug, a locale module bug, or a distro bug:
 LANG=en_IN ./python -m test -v test_re
We've only confirmed it on Ubuntu so far though - I haven't been able to reproduce it on Fedora, and Jaysinh hasn't been able to reproduce it since switching to Gentoo.

Similar issue reported on debian9.8 stretch with python 3.7.2 and en_IN : issue36134 

Ah, I can reproduce the bug on Fedora 29 using "LANG=en_IN ./python -m test -v test_re".
The problem is that locale.getlocale() is not reliable: it pretends that the locale encoding is ISO8859-1, whereas the real encoding is UTF-8:
$ LANG=en_IN ./python 
Python 3.8.0a2+ (heads/master:4cbea518a0, Feb 28 2019, 18:19:44) 
>>> chr(224).encode('ISO8859-1')
b'\xe0'
>>> import _testcapi
>>> _testcapi.DecodeLocaleEx(b'\xe0', 0, 'strict')
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
RuntimeError: decode error: pos=0, reason=decoding error
>>> import locale
# Wrong encoding
>>> locale.getlocale(locale.LC_CTYPE)
('en_IN', 'ISO8859-1')
>>> locale.setlocale(locale.LC_CTYPE, None)
'en_IN'
>>> locale._parse_localename('en_IN')
('en_IN', 'ISO8859-1')
# Real encoding
>>> locale.getpreferredencoding()
'UTF-8'
>>> locale.nl_langinfo(locale.CODESET)
'UTF-8'
Attached PR 12099 fix the issue.

> This seems to have broken test_re on Windows, see https://ci.appveyor.com/project/python/cpython/build/3.7.0a0.1
It seems like the ANSI code page is 1252 ("cp1252").
== CPython 3.7.0a0 (master:d31b28e16a2387d0251df948ef5d1b33d4357652, Mar 5 2017, 21:47:06) [MSC v.1900 32 bit (Intel)]
== Windows-2012ServerR2-6.3.9600-SP0 little-endian
== hash algorithm: siphash24 32bit
== cwd: C:\projects\cpython\build\test_python_1844
== encodings: locale=cp1252, FS=utf-8
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, ignore_environment=1, verbose=0, bytes_warning=2, quiet=0, hash_randomization=1, isolated=0)
Using random seed 5949816
...
FAIL: test_locale_flag (test.test_re.ReTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "C:\projects\cpython\lib\test\test_re.py", line 1422, in test_locale_flag
 self.assertTrue(pat.match(bletter))
AssertionError: None is not true
> getpreferredencoding() takes a completely different path on windows
> (returns a codepage) and isn't related to the C locale.
On my Windows 10 with Python 3.8, getpreferredencoding() (and getpreferredencoding(False)) returns "cp1252", getlocale(LC_CTYPE)[1] returns "1252". Python has an alias "1252" for "cp1252".
On Windows, getpreferredencoding() is implemented as _locale._getdefaultlocale()[1]. _getdefaultlocale()[1] is implemented with:
 PyOS_snprintf(encoding, sizeof(encoding), "cp%d", GetACP());
At the end, it's the ANSI code page (1252).
--
I don't understand how the change ace5c0fdd9b962e6e886c29dbcea72c53f051dc4 introduced a regression. And so I don't understand how commit 21a74312f2d1ddee71fade709af49d078085ec30 (revert) could fix anything.
--
On my PR 12099, two Windows CI run and both succeeded:
* AppVeyor: pythoninfo says "locale.encoding: cp1252"
 https://ci.appveyor.com/project/python/cpython/builds/22726025
* Windows PR Tests on Azure Pipeline: pythoninfo also says "locale.encoding: cp1252"
When the change ace5c0fdd9b962e6e886c29dbcea72c53f051dc4 was merged, Python had no working Windows CI. Things evolved at lot in the meanwhile.
I also tested manually my PR 12099 on my Windows 10 VM which also uses cp1252: test_re pass.
--
re.LOCALE flag of re.compile() for a bytes pattern uses the following function of Modules/_sre.c:
LOCAL(int)
char_loc_ignore(SRE_CODE pattern, SRE_CODE ch)
{
 return ch == pattern
 || (SRE_CODE) sre_lower_locale(ch) == pattern
 || (SRE_CODE) sre_upper_locale(ch) == pattern;
}

New changeset ab71f8b793f7b42853ccd2a127ae7720adc5bcb4 by Victor Stinner in branch 'master':
bpo-29571: Fix test_re.test_locale_flag() (GH-12099)
https://github.com/python/cpython/commit/ab71f8b793f7b42853ccd2a127ae7720adc5bcb4

AppVeyor failed on the backport to Python 3.7 of my fix: PR 12108.
Ok, now I understand the bug in Python 3.7. locale.getlocale(locale.LC_CTYPE)[1] returns None because Python doesn't set LC_CTYPE to the user preferred locale. I'm not sure of which locale is used in practice in that case, but at least I can say that None is not the expected encoding name... str.encode() and bytes.decode() use UTF-8 when None is passed as the encoding. locale.getpreferredencoding() returns 'cp1252' which is the ANSI code page.
Python 3.8 is different. In bpo-34485, I modified Python 3.8 to set LC_CTYPE locale to the user preference (ANSI code page):
---
commit 177d921c8c03d30daa32994362023f777624b10d
Author: Victor Stinner <vstinner@redhat.com>
Date: Wed Aug 29 11:25:15 2018 +0200
 bpo-34485, Windows: LC_CTYPE set to user preference (GH-8988)
 
 On Windows, the LC_CTYPE is now set to the user preferred locale at
 startup: _Py_SetLocaleFromEnv(LC_CTYPE) is now called during the
 Python initialization. Previously, the LC_CTYPE locale was "C" at
 startup, but changed when calling setlocale(LC_CTYPE, "") or
 setlocale(LC_ALL, "").
 
 pymain_read_conf() now also calls _Py_SetLocaleFromEnv(LC_CTYPE) to
 behave as _Py_InitializeCore(). Moreover, it doesn't save/restore the
 LC_ALL anymore.
 
 On Windows, standard streams like sys.stdout now always use
 surrogateescape error handler by default (ignore the locale).
---

I wrote C and Python code to check what is the effective encoding used by the LC_CTYPE locale before setlocale(LC_CTYPE, "") is called on Python 3.7. Result: Windows uses the Latin1 encoding.
See attached files: _testcapi.patch + loc.py produced loc.log (output).

New changeset 279657bac2856039ba422c18a3d7f227b455e9d6 by Victor Stinner in branch '3.7':
[3.7] bpo-29571: Fix test_re.test_locale_flag() (GH-12178)
https://github.com/python/cpython/commit/279657bac2856039ba422c18a3d7f227b455e9d6

I don't understand the relationship with bpo-20087, so I removed the dependency.
I fixed test_re in 3.7 and master branches. I close the issue.