Python not sorting unicode properly. Strcoll doesn't help

Question

I've got a problem with sorting lists using unicode collation in Python 2.5.1 and 2.6.5 on OSX, as well as on Linux.

import locale   
locale.setlocale(locale.LC_ALL, 'pl_PL.UTF-8')
print [i for i in sorted([u'a', u'z', u'ą'], cmp=locale.strcoll)]

Which should print:

[u'a', u'ą', u'z']

But instead prints out:

[u'a', u'z', u'ą']

Summing it up - it looks as if strcoll was broken. Tried it with various types of variables (fe. non-unicode encoded strings).

What do I do wrong?

Best regards, Tomasz Kopczuk.

Answer 1

Apparently, the only way for sorting to work on all platforms is to use the ICU library with PyICU bindings (PyICU on PyPI).

On OS X: sudo port install py26-pyicu, minding bug described here: https://svn.macports.org/ticket/23429 (oh the joy of using macports).

PyICUs documentation is unfortunately severely lacking, but I managed to find out how it's done:

import PyICU
collator = PyICU.Collator.createInstance(PyICU.Locale('pl_PL.UTF-8'))
print [i for i in sorted([u'a', u'z', u'ą'], cmp=collator.compare)]

which gives:

[u'a', u'ą', u'z']

Another pro - @bobince: it's thread-safe, so not useless when setting request-wise locales.

Answer 2

Just to add to tkopczuk's investigation: This is definitely a gcc bug, at least for version 4.2.1 on OS X 10.6.4. It can be reproduced by calling C strcoll() directly as in this snippet.

EDIT: Still on the same system, I find that for the UTF-8 versions of de_DE, fr_FR, pl_PL, the problem is there, but for the ISO-88591 versions of fr_FR and de_DE, sort order is correct. Unfortunately for the OP, ISO-88592 pl_PL is also buggy:

The order for Polish ISO-8859 is:
LATIN SMALL LETTER A
LATIN SMALL LETTER Z
LATIN SMALL LETTER A WITH OGONEK
The LC_COLLATE culture and encoding settings were pl_PL, ISO8859-2.

The order for Polish Unicode is:
LATIN SMALL LETTER A
LATIN SMALL LETTER Z
LATIN SMALL LETTER A WITH OGONEK
The LC_COLLATE culture and encoding settings were pl_PL, UTF8.

The order for German Unicode is:
LATIN SMALL LETTER A
LATIN SMALL LETTER Z
LATIN SMALL LETTER A WITH DIAERESIS
The LC_COLLATE culture and encoding settings were de_DE, UTF8.

The order for German ISO-8859 is:
LATIN SMALL LETTER A
LATIN SMALL LETTER A WITH DIAERESIS
LATIN SMALL LETTER Z
The LC_COLLATE culture and encoding settings were de_DE, ISO8859-1.

The order for Fremch ISO-8859 is:
LATIN SMALL LETTER A
LATIN SMALL LETTER E WITH ACUTE
LATIN SMALL LETTER Z
The LC_COLLATE culture and encoding settings were fr_FR, ISO8859-1.

The order for French Unicode is:
LATIN SMALL LETTER A
LATIN SMALL LETTER Z
LATIN SMALL LETTER E WITH ACUTE
The LC_COLLATE culture and encoding settings were fr_FR, UTF8.

Answer 3

Here is how i managed to sort Persian language correctly (without PyICU)(using python 3.x):

First set the locale (don't forget to import locale and platform)

if platform.system() == 'Linux':
    locale.setlocale(locale.LC_ALL, 'fa_IR.UTF-8')
elif platform.system() == 'Windows':
   locale.setlocale(locale.LC_ALL, 'Persian_Iran.1256')
else:
   pass (or any other OS)

Then sort using key:

a = ['ا','ب','پ','ت','ث','ج','چ','ح','خ','د','ذ','ر','ز','ژ','س','ش','ص','ض','ط','ظ','ع','غ','ف','ق','ک','گ','ل','م','ن','و','ه','ي']

print(sorted(a,key=locale.strxfrm))

For list of Objects:

a = [{'id':"ا"},{'id':"ب"},{'id':"پ"},{'id':"ت"},{'id':"ث"},{'id':"ج"},{'id':"چ"},{'id':"ح"},{'id':"خ"},{'id':"د"},{'id':"ذ"},{'id':"ر"},{'id':"ز"},{'id':"ژ"},{'id':"س"},{'id':"ش"},{'id':"ص"},{'id':"ض"},{'id':"ط"},{'id':"ظ"},{'id':"ع"},{'id':"غ"},{'id':"ف"},{'id':"ق"},{'id':"ک"},{'id':"گ"},{'id':"ل"},{'id':"م"},{'id':"ن"},{'id':"و"},{'id':"ه"},{'id':"ي"}]

print(sorted(a, key=lambda x: locale.strxfrm(x['id']))

Finally you can return the locale:

locale.setlocale(locale.LC_ALL, '')