How do I sort unicode strings alphabetically in Python?
Python sorts by byte value by default, which means é comes after z and other equally funny things. What is the best way to sort alphabetically in Python?
Is there a library for this? I couldn't find anything. Preferrably sorting should have language support so it understands that åäö should be sorted after z in Swedish, but that ü should be sorted by u, etc. Unicode support is thereby pretty much a requirement.
If there is no library for it, what is the best way to do this? Just make a mapping from letter to a integer value and map the string to a integer list with that?
Answer
IBM's ICU library does that (and a lot more). It has Python bindings: PyICU.
Update: The core difference in sorting between ICU and locale.strcoll is that ICU uses the full Unicode Collation Algorithm while strcoll uses ISO 14651.
The differences between those two algorithms are briefly summarized here: http://unicode.org/faq/collation.html#13. These are rather exotic special cases, which should rarely matter in practice.
>>> import icu # pip install PyICU
>>> sorted(['a','b','c','ä'])
['a', 'b', 'c', 'ä']
>>> collator = icu.Collator.createInstance(icu.Locale('de_DE.UTF-8'))
>>> sorted(['a','b','c','ä'], key=collator.getSortKey)
['a', 'ä', 'b', 'c']