What is the best way of creating an alphabetically sorted list in Python?
11 Answers
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)
8 Comments
jfs
mylist.sort(key=str.lower) is faster.
Eli Courtwright
Good point. I'll leave my current example as-is, since it's probably easier for a beginner to see what's happening, but I'll keep that in mind in the future.
Hari Ganesan
If anyone is curious, performance of list.sort() can be found here
jfs
@BornToCode : 1- I know. Look at the revision (2008) my comment replies to (my comment is about the unnecessary use of lambda). 2- sorting non-ASCII characters is a big separate topic. PyICU could be used instead of the locale-based solution.
bjg222
@Dmitry This is because you are printing the return value of the sort function called in
[1, 2, 3].sort(). As sort() sorts the list in place (ie, changes the list directly), it doesn't return the sorted list, and actually doesn't return anything, so your print statement prints None. If you saved your list to a variable, say x, called x.sort(), then print(x), you would see the sorted list. |
It is also worth noting the sorted() function:
for x in sorted(list):
print x
This returns a new, sorted version of a list without changing the original list.
Comments
list.sort()
It really is that simple :)
1 Comment
Volker Siegel
In general, it is surprisingly far from simple. But ok, the simplest case is actually simple.
The proper way to sort strings is:
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'), cmp=locale.strcoll) == [u'aa', u'Ab', u'ad']
# Without using locale.strcoll you get:
assert sorted((u'Ab', u'ad', u'aa')) == [u'Ab', u'aa', u'ad']
The previous example of mylist.sort(key=lambda x: x.lower()) will work fine for ASCII-only contexts.
Comments
Please use sorted() function in Python3
items = ["love", "like", "play", "cool", "my"]
sorted(items2)
Comments
But how does this handle language specific sorting rules? Does it take locale into account?
No, list.sort() is a generic sorting function. If you want to sort according to the Unicode rules, you'll have to define a custom sort key function. You can try using the pyuca module, but I don't know how complete it is.
Comments
l =['abc' , 'cd' , 'xy' , 'ba' , 'dc']
l.sort()
print(l)
Result
['abc', 'ba', 'cd', 'dc', 'xy']
Comments
Old question, but if you want to do locale-aware sorting without setting locale.LC_ALL you can do so by using the PyICU library as suggested by this answer:
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)
Then call with e.g.:
new_list = sorted_strings(list_of_strings, "de_DE.utf8")
This worked for me without installing any locales or changing other system settings.
(This was already suggested in a comment above, but I wanted to give it more prominence, because I missed it myself at first.)
Comments
Suppose s = "ZWzaAd"
To sort above string the simple solution will be below one.
print ''.join(sorted(s))
1 Comment
mnl
that is not a list of strings you are sorting here
Or maybe:
names = ['Jasmine', 'Alberto', 'Ross', 'dig-dog']
print ("The solution for this is about this names being sorted:",sorted(names, key=lambda name:name.lower()))
Comments
It is simple:
https://trinket.io/library/trinkets/5db81676e4
scores = "54 - Alice,35 - Bob,27 - Carol,27 - Chuck,05 - Craig,30 - Dan,27 - Erin,77 - Eve,14 - Fay,20 - Frank,48 - Grace,61 - Heidi,03 - Judy,28 - Mallory,05 - Olivia,44 - Oscar,34 - Peggy,30 - Sybil,82 - Trent,75 - Trudy,92 - Victor,37 - Walter"
scores = scores.split(',')
for x in sorted(scores):
print(x)
President James K. Polk
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answered Jun 3, 2020 at 2:16
Hedayatullah Sarwary
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Comments
localeand it's string collation methods to sort naturally according to current locale.