Question and Answer

how to sort a list in python

Basic answer:

  • mylist = [“b”, “C”, “A”]
  • mylist.sort()

This modifies your original list (i.e. sorts in-place). To get a sorted copy of the list, without changing the original, use the sorted() function:

  • for x in sorted(mylist):
  • print x

However, the examples above are a bit naive, because they don’t take locale into account, and perform a case-sensitive sorting. You can take advantage of the optional parameter key to specify custom sorting order (the alternative, using cmp, is a deprecated solution, as it has to be evaluated multiple times – key is only computed once per element).

So, to sort according to the current locale, taking language-specific rules into account (cmp_to_key is a helper function from functools):

  • sorted(mylist, key=cmp_to_key(locale.strcoll))

And finally, if you need, you can specify a custom locale for sorting:

  • import locale
  • locale.setlocale(locale.LC_ALL, ‘en_US.UTF-8’) # vary depending on your lang/locale
  • assert sorted((u’Ab’, u’ad’, u’aa’),
  • key=cmp_to_key(locale.strcoll)) == [u’aa’, u’Ab’, u’ad’]

Last note: you will see examples of case-insensitive sorting which use the lower() method – those are incorrect, because they work only for the ASCII subset of characters. Those two are wrong for any non-English data:

  • # this is incorrect!
  • mylist.sort(key=lambda x: x.lower())
  • # alternative notation, a bit faster, but still wrong
  • mylist.sort(key=str.lower)
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