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natsort 3.5.3

Sort lists naturally

Package Documentation

Natural sorting for python.

Please see Deprecation Notices for an important backwards incompatibility notice for natsort version 4.0.0.

Quick Description

When you try to sort a list of strings that contain numbers, the normal python sort algorithm sorts lexicographically, so you might not get the results that you expect:

>>> a = ['a2', 'a9', 'a1', 'a4', 'a10']
>>> sorted(a)
['a1', 'a10', 'a2', 'a4', 'a9']

Notice that it has the order (‘1’, ‘10’, ‘2’) - this is because the list is being sorted in lexicographical order, which sorts numbers like you would letters (i.e. ‘b’, ‘ba’, ‘c’).

natsort provides a function natsorted that helps sort lists “naturally”, either as real numbers (i.e. signed/unsigned floats or ints), or as versions. Using natsorted is simple:

>>> from natsort import natsorted
>>> a = ['a2', 'a9', 'a1', 'a4', 'a10']
>>> natsorted(a)
['a1', 'a2', 'a4', 'a9', 'a10']

natsorted identifies real numbers anywhere in a string and sorts them naturally.

Sorting version numbers is just as easy with the versorted function:

>>> from natsort import versorted
>>> a = ['version-1.9', 'version-2.0', 'version-1.11', 'version-1.10']
>>> versorted(a)
['version-1.9', 'version-1.10', 'version-1.11', 'version-2.0']
>>> natsorted(a)  # natsorted tries to sort as signed floats, so it won't work
['version-2.0', 'version-1.9', 'version-1.11', 'version-1.10']

You can also perform locale-aware sorting (or “human sorting”), where the non-numeric characters are ordered based on their meaning, not on their ordinal value; this can be achieved with the humansorted function:

>>> a = ['Apple', 'Banana', 'apple', 'banana']
>>> natsorted(a)
['Apple', 'Banana', 'apple', 'banana']
>>> import locale
>>> locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
>>> from natsort import humansorted
>>> humansorted(a)
['apple', 'Apple', 'banana', 'Banana']

You may find you need to explicitly set the locale to get this to work (as shown in the example). Please see the following caveat and the Optional Dependencies section below before using the humansorted function, especially if you are on a BSD-based system (like Mac OS X).

You can mix and match int, float, and str (or unicode) types when you sort:

>>> a = ['4.5', 6, 2.0, '5', 'a']
>>> natsorted(a)
[2.0, '4.5', '5', 6, 'a']
>>> # On Python 2, sorted(a) would return [2.0, 6, '4.5', '5', 'a']
>>> # On Python 3, sorted(a) would raise an "unorderable types" TypeError

The natsort algorithm does other fancy things like

  • recursively descend into lists of lists
  • control the case-sensitivity
  • sort file paths correctly
  • allow custom sorting keys
  • exposes a natsort_key generator to pass to list.sort

Please see the package documentation for more details, including examples and recipes.

Shell script

natsort comes with a shell script called natsort, or can also be called from the command line with python -m natsort.


natsort requires python version 2.6 or greater (this includes python 3.x). To run version 2.6, 3.0, or 3.1 the argparse module is required.

Optional Dependencies


The most efficient sorting can occur if you install the fastnumbers package (it helps with the string to number conversions.) natsort will still run (efficiently) without the package, but if you need to squeeze out that extra juice it is recommended you include this as a dependency. natsort will not require (or check) that fastnumbers is installed at installation.


On BSD-based systems (this includes Mac OS X), the underlying locale library can be buggy (please see, so natsort will use PyICU under the hood if it is installed on your computer; this will give more reliable cross-platform results. natsort will not require (or check) that PyICU is installed at installation since in Linux-based systems and Windows systems locale should work just fine. Please visit for more details and how to install on Mac OS X.

Deprecation Notices

  • The default sorting algorithm for natsort will change in version 4.0.0 from signed floats (with exponents) to unsigned integers. The motivation for this change is that it will cause natsort to return results that pass the “least astonishment” test for the most common use case, which is sorting version numbers. If you currently rely on the default behavior to be signed floats, it is recommend that you add alg=ns.F to your natsort calls.
  • In natsort version 4.0.0, the number_type, signed, exp, as_path, and py3_safe options will be removed from the (documented) API, in favor of the alg option and ns enum. They will remain as keyword-only arguments after that (for the foreseeable future).
  • In natsort version 4.0.0, the natsort_key function will be removed from the public API. All future development should use natsort_keygen in preparation for this.


Seth M. Morton


These are the last three entries of the changelog. See the package documentation for the complete changelog.

03-26-2015 v. 3.5.3

  • Fixed bug where --reverse-filter option in shell script was not getting checked for correctness.
  • Documentation updates to better describe locale bug, and illustrate upcoming default behavior change.
  • Internal improvements, including making test suite more granular.

01-13-2015 v. 3.5.2

  • Enhancement that will convert a ‘pathlib.Path’ object to a ‘str’ if ‘ns.PATH’ is enabled.

09-25-2014 v. 3.5.1

  • Fixed bug that caused list/tuples to fail when using ‘ns.LOWECASEFIRST’ or ‘ns.IGNORECASE’.
  • Refactored modules so that only the public API was in and
  • Refactored all import statements to be absolute, not relative.
File Type Py Version Uploaded on Size
natsort-3.5.3-py2.py3-none-any.whl (md5) Python Wheel 2.7 2015-03-27 24KB
natsort-3.5.3.tar.gz (md5) Source 2015-03-27 42KB (md5) Source 2015-03-27 60KB
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