Sorting dicts (contained in lists) alphanumerically in Python

Question

I'm having an issue with sorting a list that contains a dict. Currently I am sorting it by a key called 'title' with the following line:

list.sort(key=operator.itemgetter('title'))

The problem with this is that some of my data gets sorted looking like this:

title_text #49
title_text #5
title_text #50

How would I go about sorting it in a way that is more friendly for human consumption while still maintaining the title sort?

any chance you can make your numbers 0-padded on the left? i.e. title_text #5 to be `title_text #05` - then you won't need to 'fix' the sort — Nas Banov, Jul 13 '10 at 05:44

unutbu · Accepted Answer · 2010-07-12T19:43:53.387

You are looking for human sorting.

import re
# Source: http://nedbatchelder.com/blog/200712/human_sorting.html
# Author: Ned Batchelder
def tryint(s):
    try:
        return int(s)
    except:
        return s

def alphanum_key(s):
    """ Turn a string into a list of string and number chunks.
        "z23a" -> ["z", 23, "a"]
    """
    return [ tryint(c) for c in re.split('([0-9]+)', s) ]

def sort_nicely(l):
    """ Sort the given list in the way that humans expect.
    """
    l.sort(key=alphanum_key)

data=[
    'title_text #49',
    'title_text #5',
    'title_text #50']
sort_nicely(data)
print(data)
# ['title_text #5', 'title_text #49', 'title_text #50']

Edit: If your data is a list of dicts then:

data=[{'title': 'title_text #49', 'x':0},
      {'title':'title_text #5', 'x':10},
      {'title': 'title_text #50','x':20}]

data.sort(key=lambda x: alphanum_key(x['title']))
# [{'x': 10, 'title': 'title_text #5'}, {'x': 0, 'title': 'title_text #49'}, {'x': 20, 'title': 'title_text #50'}]

I got that far, but how would you do that if your data contained a dict with multiple values including the title (which I am wanting to sort with)? — wierddemon, Jul 12 '10 at 19:15
@wierddemon: The heart of the human sorting technique lies in `alphanum_key`. For a list of dicts, you could use it like this: `data.sort(key=lambda x: alphanum_key(x['title']))`. See above. — unutbu, Jul 12 '10 at 19:44

score 2 · Answer 2 · edited May 23 '17 at 10:27

2

You're looking for a Natural Sort. Start here:

Python analog of natsort function (sort a list using a "natural order" algorithm)

edited May 23 '17 at 10:27

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answered Jul 12 '10 at 19:04

Mark Ransom

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score 0 · Answer 3 · answered Jul 12 '10 at 19:09

You'll have to parse that integer from the title manually. This function will do it.

def parse_title_num(title):
   val = 0
   try:
      val = int(title.rsplit('#')[-1])
   except ValueError:
      pass
   return val


 list.sort(key=lambda x: parse_title_num(x['title'])

Sorting dicts (contained in lists) alphanumerically in Python

3 Answers3