Silver Light Silver Light - 2 months ago 19
Python Question

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

I would like to know if there is something similar to PHP natsort function in Python?

l = ['image1.jpg', 'image15.jpg', 'image12.jpg', 'image3.jpg']


['image1.jpg', 'image12.jpg', 'image15.jpg', 'image3.jpg']

but I would like to get:

['image1.jpg', 'image3.jpg', 'image12.jpg', 'image15.jpg']


Solution base on this link

def try_int(s):
"Convert to integer if possible."
try: return int(s)
except: return s

def natsort_key(s):
"Used internally to get a tuple by which s is sorted."
import re
return map(try_int, re.findall(r'(\d+|\D+)', s))

def natcmp(a, b):
"Natural string comparison, case sensitive."
return cmp(natsort_key(a), natsort_key(b))

def natcasecmp(a, b):
"Natural string comparison, ignores case."
return natcmp(a.lower(), b.lower())


Answer Source

From my answer to Natural Sorting algorithm:

import re
def natural_key(string_):
    return [int(s) if s.isdigit() else s for s in re.split(r'(\d+)', string_)]


>>> L = ['image1.jpg', 'image15.jpg', 'image12.jpg', 'image3.jpg']
>>> sorted(L)
['image1.jpg', 'image12.jpg', 'image15.jpg', 'image3.jpg']
>>> sorted(L, key=natural_key)
['image1.jpg', 'image3.jpg', 'image12.jpg', 'image15.jpg']

To support Unicode strings, .isdecimal() should be used instead of .isdigit(). See example in @phihag's comment. Related: How to reveal Unicodes numeric value property.

.isdigit() may also fail (return value that is not accepted by int()) for a bytestring on Python 2 in some locales e.g., '\xb2' ('²') in cp1252 locale on Windows.