Python Numerical Sorting of Strings

Question

How do I make Python sorting behave like sort -n from GNU coreutils?

This is my images.txt:

Vol. 1/Vol. 1 - Special 1/002.png
Vol. 1/Chapter 2 example text/002.png
Vol. 1/Vol. 1 Extra/002.png
Vol. 1/Chapter 2 example text/001.png
Vol. 1/Vol. 1 Extra/001.png
Vol. 1/Chapter 1 example text/002.png
Vol. 1/Vol. 1 - Special 1/001.png
Vol. 1/Chapter 1 example text/001.png

When I run this Bash script:

#!/bin/bash

cat images.txt | sort -n

I get the following output:

Vol. 1/Chapter 1 example text/001.png
Vol. 1/Chapter 1 example text/002.png
Vol. 1/Chapter 2 example text/001.png
Vol. 1/Chapter 2 example text/002.png
Vol. 1/Vol. 1 Extra/001.png
Vol. 1/Vol. 1 Extra/002.png
Vol. 1/Vol. 1 - Special 1/001.png
Vol. 1/Vol. 1 - Special 1/002.png

But when I run this Python script:

#!/usr/bin/env python3

images = []

with open("images.txt") as images_file:
    for image in images_file:
        images.append(image)

images = sorted(images)

for image in images:
    print(image, end="")

I get the following output, which is not what I need:

Vol. 1/Chapter 1 example text/001.png
Vol. 1/Chapter 1 example text/002.png
Vol. 1/Chapter 2 example text/001.png
Vol. 1/Chapter 2 example text/002.png
Vol. 1/Vol. 1 - Special 1/001.png
Vol. 1/Vol. 1 - Special 1/002.png
Vol. 1/Vol. 1 Extra/001.png
Vol. 1/Vol. 1 Extra/002.png

How do I achieve the same result with Python that I achieve with Bash and sort -n?

Possible duplicate of Does Python have a built in function for string natural sort? — roganjosh
– roganjosh, Commented Oct 29, 2018 at 17:35
I'm not sure there's an in-built method, seems like - is treated differently. Maybe sorted(L, key=lambda x: x.replace(' - ', ' ')) ? — jpp
– jpp, Commented Oct 29, 2018 at 17:36
I am missing the "numerical" part of your question. The numbers are sorted equally in both examples. — Jongware
– Jongware, Commented Oct 29, 2018 at 17:36
@jpp Thank you, that works. Can you please submit your solution as an answer so I can accept it? — user9593274
– user9593274, Commented Oct 29, 2018 at 17:44

jpp · Accepted Answer · 2018-10-29 17:47:46Z

2

While I'm no gnu expert, it seems '-' is ordered differently versus Python. A quick fix for this particular issue is to replace ' - ' with ' ' when sorting:

L = sorted(L, key=lambda x: x.replace(' - ', ' '))

answered Oct 29, 2018 at 17:47

jpp

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Spencer Post · Accepted Answer · 2018-10-29 17:54:29Z

0

You might also want to consider a lambda which replaces all non alpha numeric characters

images = sorted(images, key=lambda x: re.sub('[^A-Za-z\d]+', '', x))

answered Oct 29, 2018 at 17:54

Spencer Post

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