Code snippet: Natural string sorting

[C. Barnes]

Summary:

Sorts strings in a way that seems natural to humans.
If the
strings contain integers, then the integers are
ordered
numerically. For example, sorts ['Team 11', 'Team 3',
'Team 1']
into the order ['Team 1', 'Team 3', 'Team 11'].

Code:

#
---------------------------------------------------------
# natsort.py: Natural string sorting.
#
---------------------------------------------------------

# By Seo Sanghyeon. Some changes by Connelly Barnes.

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())

def natsort(seq, cmp=natcmp):
"In-place natural string sort."
seq.sort(cmp)

def natsorted(seq, cmp=natcmp):
"Returns a copy of seq, sorted by natural string
sort."
import copy
temp = copy.copy(seq)
natsort(temp, cmp)
return temp

Examples:

You can use this code to sort tarball filenames:

natsorted(['ver-1.3.12', 'ver-1.3.3', 'ver-1.2.5', 'ver-1.2.15', 'ver-1.2.3', 'ver-1.2.1'])
['ver-1.2.1', 'ver-1.2.3', 'ver-1.2.5', 'ver-1.2.15',
'ver-1.3.3', 'ver-1.3.12']

Chemical elements:
natsorted(['C1H2', 'C1H4', 'C2H2', 'C2H6', 'C2N', 'C3H6'])
['C1H2', 'C1H4', 'C2H2', 'C2H6', 'C2N', 'C3H6']

Teams:
natsorted(['Team 101', 'Team 58', 'Team 30', 'Team 1'])
['Team 1', 'Team 30', 'Team 58', 'Team 101']

Pass natcasecmp as a second argument for
case-insensitive sorting:
natsorted(['a5', 'A7', 'a15', 'a9', 'A8'],

natcasecmp)
['a5', 'A7', 'A8', 'a9', 'a15']

Enjoy!
Message and source code are in the public domain.


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