Sorting list of string with specific locale in python

Question

I work on an application that uses texts from different languages, so, for viewing or reporting purposes, some texts (strings) need to be sorted in a specific language.

Currently I have a workaround messing with the global locale settings, which is bad, and I don't want to put it in production:

default_locale = locale.getlocale(locale.LC_COLLATE)

def sort_strings(strings, locale_=None):
    if locale_ is None:
        return sorted(strings)

    locale.setlocale(locale.LC_COLLATE, locale_)
    sorted_strings = sorted(strings, cmp=locale.strcoll)
    locale.setlocale(locale.LC_COLLATE, default_locale)

    return sorted_strings

The official python locale documentation explicitly says that saving and restoring is a bad idea, but does not give any suggestions: http://docs.python.org/library/locale.html#background-details-hints-tips-and-caveats

Answer 1

You could use a PyICU's collator to avoid changing global settings:

import icu # PyICU

def sorted_strings(strings, locale=None):
    if locale is None:
       return sorted(strings)
    collator = icu.Collator.createInstance(icu.Locale(locale))
    return sorted(strings, key=collator.getSortKey)

Example:

>>> L = [u'sandwiches', u'angel delight', u'custard', u'éclairs', u'glühwein']
>>> sorted_strings(L)
['angel delight', 'custard', 'glühwein', 'sandwiches', 'éclairs']
>>> sorted_strings(L, 'en_US')
['angel delight', 'custard', 'éclairs', 'glühwein', 'sandwiches']

Disadvantage: dependency on PyICU library; the behavior is slightly different from locale.strcoll.

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I don't know how to get locale.strxfrm function given a locale name without changing it globally. As a hack you could run your function in a different child process:

pool = multiprocessing.Pool()
# ...
pool.apply(locale_aware_sort, [strings, loc])

Disadvantage: might be slow, resource hungry

---

Using ordinary threading.Lock won't work unless you can control every place where locale aware functions (they are not limited to locale module e.g., re) could be called from multiple threads.

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You could compile your function using Cython to synchronize access using GIL. GIL will make sure that no other Python code can be executed while your function is running.

Disadvantage: not pure Python