python - How do you sort files numerically?

Question

I'm processing some files in a directory and need the files to be sorted numerically. I found some examples on sorting--specifically with using the lambda pattern--at wiki.python.org, and I put this together:

#!env/python
import re

tiffFiles = """ayurveda_1.tif
ayurveda_11.tif
ayurveda_13.tif
ayurveda_2.tif
ayurveda_20.tif
ayurveda_22.tif""".split('
')

numPattern = re.compile('_(d{1,2}).', re.IGNORECASE)

tiffFiles.sort(cmp, key=lambda tFile:
                   int(numPattern.search(tFile).group(1)))

print tiffFiles

I'm still rather new to Python and would like to ask the community if there are any improvements that can be made to this: shortening the code up (removing lambda), performance, style/readability?

Thank you, Zachary

Answer 1

This is called "natural sorting" or "human sorting" (as opposed to lexicographical sorting, which is the default). Ned B wrote up a quick version of one.

import re

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)

It's similar to what you're doing, but perhaps a bit more generalized.