Sorting a list which has numbers in the form of string in python

Question

I have list of numbers which is in the form of string and I want to sort the numbers in it. How do I sort such numbers in python?

Here is my list.

key_s=['115', '114', '117', '116', '111', '110', '113', '112', '68', '119', '118', '44', '45', '42', '43', '41', '76', '108', '109', '71', '107', '79', '13', '15', '14', '17', '16', '37']

I tried using key_s.sort().It returns None instead of sorted array. I even tried sorted(key_s) which is even not working. So what is the solution to sort it?

sorted(key_s, key=int) - for more details [read documentation](https://docs.python.org/2/library/functions.html#sorted) — AndreyT, Apr 05 '16 at 11:02
@Dhruv: are you trying to win the functional paradigm abuse award there? — Martijn Pieters, Apr 05 '16 at 11:51
@Dhruv: mapping to int, sorting, then mapping back to string is hugely inefficient. Use `sorted(key_s, key=int)`, no need to map back to strings again, or create 2 intermediate list objects if you are using Python 2. — Martijn Pieters, Apr 05 '16 at 12:04

Martijn Pieters · Answer 1 · 2016-04-05T11:12:23.307

Yes, list.sort() sorts in place, and returns None to indicate it is the list itself that has been sorted. The sorted() function returns a new sorted list, leaving the original list unchanged.

Use int as a key:

sorted(key_s, key=int)

This returns a new list, sorted by the numeric value of each string, but leaving the type of the values themselves unchanged.

Without a key, strings are sorted lexicographically instead, comparing character by character. Thus '9' is sorted after '10', because the character '1' comes before '9' in character sets, just like 'a' comes before 'z'.

The key argument lets you apply a Schwartzian_transform, informing the sorting algorithm what to sort by. Each value in the list is sorted according to key(value) (so int(value) here) instead of the original value itself.

Demo:

>>> key_s = ['115', '114', '117', '116', '111', '110', '113', '112', '68', '119', '118', '44', '45', '42', '43', '41', '76', '108', '109', '71', '107', '79', '13', '15', '14', '17', '16', '37']
>>> sorted(key_s, key=int)
['13', '14', '15', '16', '17', '37', '41', '42', '43', '44', '45', '68', '71', '76', '79', '107', '108', '109', '110', '111', '112', '113', '114', '115', '116', '117', '118', '119']

@Martijin Oh alright. Thank you – Karthik Hegde Apr 05 '16 at 11:05 — Karthik Hegde, Apr 05 '16 at 11:05
Good explanation. up-voted. can you explain more on `key` ? – Vivek Sable Apr 05 '16 at 11:10 — Vivek Sable, Apr 05 '16 at 11:10

Sorting a list which has numbers in the form of string in python

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