How to Achieve Natural Order Sorting in Python Like PHP's natsort?

Python's Equivalent to PHP's natsort for Natural Order Sorting

A frequently asked question in Python is how to sort a list in natural order, similar to PHP's natsort function. Unlike a standard sort, natural order considers numeric characters as numbers rather than strings.

For instance, consider sorting a list of filenames:

<code class="python">l = ['image1.jpg', 'image15.jpg', 'image12.jpg', 'image3.jpg']
l.sort()</code>

This standard sorting will result in:

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

However, to achieve a natural order sorting, Python provides a key function that converts strings into numeric tuples if possible. This allows for proper numeric comparisons.

Here's a sample implementation:

<code class="python">import re

def natsort_key(s):
    return map(int, re.findall(r'(\d+)', s))</code>

Applying this key during sorting yields the desired natural order:

<code class="python">l.sort(key=natsort_key)</code>

The output will be:

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

Alternatively, if you require case-insensitive sorting, a more complete implementation can be used:

<code class="python">def natcasecmp(a, b):
    return natcmp(a.lower(), b.lower())</code>

This provides a case-insensitive natural order sorting.

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