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Description:

natsort 8.4.0

Simple yet flexible natural sorting in Python.

Source Code: https://github.com/SethMMorton/natsort
Downloads: https://pypi.org/project/natsort/
Documentation: https://natsort.readthedocs.io/

Examples and Recipes
How Does Natsort Work?
API

Quick Description
Quick Examples
FAQ
Requirements
Optional Dependencies
Installation
How to Run Tests
How to Build Documentation
Dropped Deprecated APIs
History

NOTE: Please see the Dropped Deprecated APIs section for changes.

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 = ['2 ft 7 in', '1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '7 ft 6 in']
>>> sorted(a)
['1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '2 ft 7 in', '7 ft 6 in']
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” (“naturally” is rather ill-defined, but in general it means
sorting based on meaning and not computer code point).
Using natsorted() is simple:
>>> from natsort import natsorted
>>> a = ['2 ft 7 in', '1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '7 ft 6 in']
>>> natsorted(a)
['1 ft 5 in', '2 ft 7 in', '2 ft 11 in', '7 ft 6 in', '10 ft 2 in']
natsorted() identifies numbers anywhere in a string and sorts them
naturally. Below are some other things you can do with natsort
(also see the Examples and Recipes for a quick start guide, or the
API for complete details).
Note: natsorted() is designed to be a drop-in replacement for the
built-in sorted() function. Like sorted(), natsorted()
does not sort in-place. To sort a list and assign the output to the same
variable, you must explicitly assign the output to a variable:
>>> a = ['2 ft 7 in', '1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '7 ft 6 in']
>>> natsorted(a)
['1 ft 5 in', '2 ft 7 in', '2 ft 11 in', '7 ft 6 in', '10 ft 2 in']
>>> print(a) # 'a' was not sorted; "natsorted" simply returned a sorted list
['2 ft 7 in', '1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '7 ft 6 in']
>>> a = natsorted(a) # Now 'a' will be sorted because the sorted list was assigned to 'a'
>>> print(a)
['1 ft 5 in', '2 ft 7 in', '2 ft 11 in', '7 ft 6 in', '10 ft 2 in']
Please see Generating a Reusable Sorting Key and Sorting In-Place for
an alternate way to sort in-place naturally.

Quick Examples

Sorting Versions
Sort Paths Like My File Browser (e.g. Windows Explorer on Windows)
Sorting by Real Numbers (i.e. Signed Floats)
Locale-Aware Sorting (or “Human Sorting”)
Further Customizing Natsort
Sorting Mixed Types
Handling Bytes
Generating a Reusable Sorting Key and Sorting In-Place
Other Useful Things

Sorting Versions
natsort does not actually comprehend version numbers.
It just so happens that the most common versioning schemes are designed to
work with standard natural sorting techniques; these schemes include
MAJOR.MINOR, MAJOR.MINOR.PATCH, YEAR.MONTH.DAY. If your data
conforms to a scheme like this, then it will work out-of-the-box with
natsorted() (as of natsort version >= 4.0.0):
>>> a = ['version-1.9', 'version-2.0', 'version-1.11', 'version-1.10']
>>> natsorted(a)
['version-1.9', 'version-1.10', 'version-1.11', 'version-2.0']
If you need to versions that use a more complicated scheme, please see
these version sorting examples.

Sort Paths Like My File Browser (e.g. Windows Explorer on Windows)
Prior to natsort version 7.1.0, it was a common request to be able to
sort paths like Windows Explorer. As of natsort 7.1.0, the function
os_sorted() has been added to provide users the ability to sort
in the order that their file browser might sort (e.g Windows Explorer on
Windows, Finder on MacOS, Dolphin/Nautilus/Thunar/etc. on Linux).
import os
from natsort import os_sorted
print(os_sorted(os.listdir()))
# The directory sorted like your file browser might show
Output will be different depending on the operating system you are on.
For users not on Windows (e.g. MacOS/Linux) it is strongly recommended
to also install PyICU, which will help
natsort give results that match most file browsers. If this is not installed,
it will fall back on Python’s built-in locale module and will give good
results for most input, but will give poor results for special characters.

Sorting by Real Numbers (i.e. Signed Floats)
This is useful in scientific data analysis (and was the default behavior
of natsorted() for natsort version < 4.0.0). Use the realsorted()
function:
>>> from natsort import realsorted, ns
>>> # Note that when interpreting as signed floats, the below numbers are
>>> # +5.10, -3.00, +5.30, +2.00
>>> a = ['position5.10.data', 'position-3.data', 'position5.3.data', 'position2.data']
>>> natsorted(a)
['position2.data', 'position5.3.data', 'position5.10.data', 'position-3.data']
>>> natsorted(a, alg=ns.REAL)
['position-3.data', 'position2.data', 'position5.10.data', 'position5.3.data']
>>> realsorted(a) # shortcut for natsorted with alg=ns.REAL
['position-3.data', 'position2.data', 'position5.10.data', 'position5.3.data']

Locale-Aware Sorting (or “Human Sorting”)
This is where the non-numeric characters are also ordered based on their
meaning, not on their ordinal value, and a locale-dependent thousands
separator and decimal separator is accounted for in the number.
This can be achieved with the humansorted() function:
>>> a = ['Apple', 'apple15', 'Banana', 'apple14,689', 'banana']
>>> natsorted(a)
['Apple', 'Banana', 'apple14,689', 'apple15', 'banana']
>>> import locale
>>> locale.setlocale(locale.LC_ALL, 'en_US.UTF-8')
'en_US.UTF-8'
>>> natsorted(a, alg=ns.LOCALE)
['apple15', 'apple14,689', 'Apple', 'banana', 'Banana']
>>> from natsort import humansorted
>>> humansorted(a) # shortcut for natsorted with alg=ns.LOCALE
['apple15', 'apple14,689', '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 locale issues and the
Optional Dependencies section below before using the humansorted() function.

Further Customizing Natsort
If you need to combine multiple algorithm modifiers (such as ns.REAL,
ns.LOCALE, and ns.IGNORECASE), you can combine the options using the
bitwise OR operator (|). For example,
>>> a = ['Apple', 'apple15', 'Banana', 'apple14,689', 'banana']
>>> natsorted(a, alg=ns.REAL | ns.LOCALE | ns.IGNORECASE)
['Apple', 'apple15', 'apple14,689', 'Banana', 'banana']
>>> # The ns enum provides long and short forms for each option.
>>> ns.LOCALE == ns.L
True
>>> # You can also customize the convenience functions, too.
>>> natsorted(a, alg=ns.REAL | ns.LOCALE | ns.IGNORECASE) == realsorted(a, alg=ns.L | ns.IC)
True
>>> natsorted(a, alg=ns.REAL | ns.LOCALE | ns.IGNORECASE) == humansorted(a, alg=ns.R | ns.IC)
True
All of the available customizations can be found in the documentation for
the ns enum.
You can also add your own custom transformation functions with the key
argument. These can be used with alg if you wish.
>>> a = ['apple2.50', '2.3apple']
>>> natsorted(a, key=lambda x: x.replace('apple', ''), alg=ns.REAL)
['2.3apple', 'apple2.50']

Sorting Mixed Types
You can mix and match int, float, and str types when you sort:
>>> a = ['4.5', 6, 2.0, '5', 'a']
>>> natsorted(a)
[2.0, '4.5', '5', 6, 'a']
>>> # sorted(a) would raise an "unorderable types" TypeError

Handling Bytes
natsort does not officially support the bytes type, but
convenience functions are provided that help you decode to str first:
>>> from natsort import as_utf8
>>> a = [b'a', 14.0, 'b']
>>> # natsorted(a) would raise a TypeError (bytes() < str())
>>> natsorted(a, key=as_utf8) == [14.0, b'a', 'b']
True
>>> a = [b'a56', b'a5', b'a6', b'a40']
>>> # natsorted(a) would return the same results as sorted(a)
>>> natsorted(a, key=as_utf8) == [b'a5', b'a6', b'a40', b'a56']
True

Generating a Reusable Sorting Key and Sorting In-Place
Under the hood, natsorted() works by generating a custom sorting
key using natsort_keygen() and then passes that to the built-in
sorted(). You can use the natsort_keygen() function yourself to
generate a custom sorting key to sort in-place using the list.sort()
method.
>>> from natsort import natsort_keygen
>>> natsort_key = natsort_keygen()
>>> a = ['2 ft 7 in', '1 ft 5 in', '10 ft 2 in', '2 ft 11 in', '7 ft 6 in']
>>> natsorted(a) == sorted(a, key=natsort_key)
True
>>> a.sort(key=natsort_key)
>>> a
['1 ft 5 in', '2 ft 7 in', '2 ft 11 in', '7 ft 6 in', '10 ft 2 in']
All of the algorithm customizations mentioned in the
Further Customizing Natsort section can also be applied to
natsort_keygen() through the alg keyword option.

Other Useful Things

recursively descend into lists of lists
automatic unicode normalization of input data
controlling the case-sensitivity
sorting file paths correctly
allow custom sorting keys
accounting for units

FAQ

How do I debug natsorted()?
The best way to debug natsorted() is to generate a key using natsort_keygen()
with the same options being passed to natsorted(). One can take a look at
exactly what is being done with their input using this key - it is highly
recommended to look at this issue describing how to debug for how to debug,
and also to review the How Does Natsort Work? page for why natsort is
doing that to your data.
If you are trying to sort custom classes and running into trouble, please
take a look at https://github.com/SethMMorton/natsort/issues/60. In short,
custom classes are not likely to be sorted correctly if one relies
on the behavior of __lt__ and the other rich comparison operators in
their custom class - it is better to use a key function with
natsort, or use the natsort key as part of your rich comparison
operator definition.

natsort gave me results I didn’t expect, and it’s a terrible library!
Did you try to debug using the above advice? If so, and you still cannot figure out
the error, then please file an issue.

How does natsort work?
If you don’t want to read How Does Natsort Work?,
here is a quick primer.
natsort provides a key function that can be passed to list.sort()
or sorted() in order to modify the default sorting behavior. This key
is generated on-demand with the key generator natsort_keygen().
natsorted() is essentially a wrapper for the following code:
>>> from natsort import natsort_keygen
>>> natsort_key = natsort_keygen()
>>> sorted(['1', '10', '2'], key=natsort_key)
['1', '2', '10']
Users can further customize natsort sorting behavior with the key
and/or alg options (see details in the Further Customizing Natsort
section).
The key generated by natsort_keygen() always returns a tuple. It
does so in the following way (some details omitted for clarity):

Assume the input is a string, and attempt to split it into numbers and
non-numbers using regular expressions. Numbers are then converted into
either int or float.
If the above fails because the input is not a string, assume the input
is some other sequence (e.g. list or tuple), and recursively
apply the key to each element of the sequence.
If the above fails because the input is not iterable, assume the input
is an int or float, and just return the input in a tuple.

Because a tuple is always returned, a TypeError should not be common
unless one tries to do something odd like sort an int against a list.

Shell script
natsort comes with a shell script called natsort, or can also be called
from the command line with python -m natsort. Check out the
shell script wiki documentation for more details.

Requirements
natsort requires Python 3.7 or greater.

Optional Dependencies

fastnumbers
The most efficient sorting can occur if you install the
fastnumbers package
(version >=2.0.0); 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.

PyICU
It is recommended that you install PyICU if you wish to sort in a
locale-dependent manner, see this page on locale issues for an explanation why.

Installation
Use pip!
$ pip install natsort
If you want to install the Optional Dependencies, you can use the
“extras” notation at installation time to install those dependencies as
well - use fast for fastnumbers and icu for PyICU.
# Install both optional dependencies.
$ pip install natsort[fast,icu]
# Install just fastnumbers
$ pip install natsort[fast]

How to Run Tests
Please note that natsort is NOT set-up to support python setup.py test.
The recommended way to run tests is with tox. After installing tox,
running tests is as simple as executing the following in the natsort directory:
$ tox
tox will create virtual a virtual environment for your tests and install
all the needed testing requirements for you. You can specify a particular
python version with the -e flag, e.g. tox -e py36. Static analysis
is done with tox -e flake8. You can see all available testing environments
with tox --listenvs.

How to Build Documentation
If you want to build the documentation for natsort, it is recommended to
use tox:
$ tox -e docs
This will place the documentation in build/sphinx/html.

Dropped Deprecated APIs
In natsort version 6.0.0, the following APIs and functions were removed

number_type keyword argument (deprecated since 3.4.0)
signed keyword argument (deprecated since 3.4.0)
exp keyword argument (deprecated since 3.4.0)
as_path keyword argument (deprecated since 3.4.0)
py3_safe keyword argument (deprecated since 3.4.0)
ns.TYPESAFE (deprecated since version 5.0.0)
ns.DIGIT (deprecated since version 5.0.0)
ns.VERSION (deprecated since version 5.0.0)
versorted() (discouraged since version 4.0.0,
officially deprecated since version 5.5.0)
index_versorted() (discouraged since version 4.0.0,
officially deprecated since version 5.5.0)

In general, if you want to determine if you are using deprecated APIs you
can run your code with the following flag
$ python -Wdefault::DeprecationWarning my-code.py
By default DeprecationWarnings are not shown, but this will cause them
to be shown. Alternatively, you can just set the environment variable
PYTHONWARNINGS to “default::DeprecationWarning” and then run your code.

Author
Seth M. Morton

History
Please visit the changelog on GitHub.