Hijacking locale.getpreferredencoding() is maybe dangerous. I attached a
new patch, force_ascii.patch, which uses a different approach: be more
strict than mbstowcs(), force the ASCII encoding when:
 - the LC_CTYPE locale is C
 - nl_langinfo(CODESET) is ASCII or an alias of ASCII
 - mbstowcs() is able to decode non-ASCII characters

2012/11/12 STINNER Victor <report@bugs.python.org>

>
> STINNER Victor added the comment:
>
> Some tests are failing with the patch:
>
> ======================================================================
> FAIL: test_undecodable_env (test.test_subprocess.POSIXProcessTestCase)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "/usr/home/haypo/prog/python/default/Lib/test/test_subprocess.py",
> line 1606, in test_undecodable_env
>     self.assertEqual(stdout.decode('ascii'), ascii(value))
> AssertionError: "'abc\\xff'" != "'abc\\udcff'"
> - 'abc\xff'
> ?      ^
> + 'abc\udcff'
> ?      ^^^
>
> ======================================================================
> FAIL: test_strcoll_with_diacritic (test.test_locale.TestEnUSCollation)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "/usr/home/haypo/prog/python/default/Lib/test/test_locale.py", line
> 364, in test_strcoll_with_diacritic
>     self.assertLess(locale.strcoll('\xe0', 'b'), 0)
> AssertionError: 126 not less than 0
>
> ======================================================================
> FAIL: test_strxfrm_with_diacritic (test.test_locale.TestEnUSCollation)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "/usr/home/haypo/prog/python/default/Lib/test/test_locale.py", line
> 367, in test_strxfrm_with_diacritic
>     self.assertLess(locale.strxfrm('\xe0'), locale.strxfrm('b'))
> AssertionError: '\xe0' not less than 'b'
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue16455>
> _______________________________________
>