Sort lists naturally
Project description
Natural sorting for python. 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.
natsort comes with a shell script that is described below. You can also execute natsort from the command line with python m natsort.
Problem Statement
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. ‘a’, ‘at’, ‘b’). It would be better if you had a sorting algorithm that recognized numbers as numbers and treated them like numbers, not letters.
This is where natsort comes in: it provides a key that helps sort lists “naturally”. It provides support for ints and floats (including negatives and exponential notation), and also a function specifically for sorting version numbers.
Synopsis
Using natsort is simple:
>>> from natsort import natsorted >>> a = ['a2', 'a9', 'a1', 'a4', 'a10'] >>> natsorted(a) ['a1', 'a2', 'a4', 'a9', 'a10']
natsort identifies the numbers and sorts them separately from strings.
You can also 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 will recursively descend into lists of lists so you can sort by the sublist contents:
>>> data = [['a1', 'a5'], ['a1', 'a40'], ['a10', 'a1'], ['a2', 'a5']] >>> sorted(data) [['a1', 'a40'], ['a1', 'a5'], ['a10', 'a1'], ['a2', 'a5']] >>> natsorted(data) [['a1', 'a5'], ['a1', 'a40'], ['a2', 'a5'], ['a10', 'a1']]
There is also a special convenience function provided that is best for sorting version numbers:
>>> from natsort import versorted >>> a = ['ver2.9.9a', 'ver1.11', 'ver2.9.9b', 'ver1.11.4', 'ver1.10.1'] >>> versorted(a) ['ver1.10.1', 'ver1.11', 'ver1.11.4', 'ver2.9.9a', 'ver2.9.9b']
The Sorting Algorithms
Sometimes you want to sort by floats, sometimes by ints, and sometimes simply by digits. natsort supports all three number types. They can be chosen with the number_type argument to natsorted.
Sort by floats
By default, natsort searches for floats (even in exponential notation!). This means that it will look for things like negative signs and decimal points when determining a number:
>>> a = ['a50', 'a51.', 'a50.4', 'a5.034e1', 'a50.300'] >>> sorted(a) ['a5.034e1', 'a50', 'a50.300', 'a50.4', 'a51.'] >>> natsorted(a, number_type=float) ['a50', 'a50.300', 'a5.034e1', 'a50.4', 'a51.'] >>> natsorted(a) # Float is the default behavior ['a50', 'a50.300', 'a5.034e1', 'a50.4', 'a51.']
Sort by ints
In some cases you don’t want natsort to identify your numbers as floats, particularly if you are sorting version numbers. This is because you want the version ‘1.10’ to come after ‘1.2’, not before. In that case, it is advantageous to sort by ints, not floats:
>>> a = ['ver1.9.9a', 'ver1.11', 'ver1.9.9b', 'ver1.11.4', 'ver1.10.1'] >>> sorted(a) ['ver1.10.1', 'ver1.11', 'ver1.11.4', 'ver1.9.9a', 'ver1.9.9b'] >>> natsorted(a) ['ver1.10.1', 'ver1.11', 'ver1.11.4', 'ver1.9.9a', 'ver1.9.9b'] >>> natsorted(a, number_type=int) ['ver1.9.9a', 'ver1.9.9b', 'ver1.10.1', 'ver1.11', 'ver1.11.4']
Sort by digits (best for version numbers)
The only difference between sorting by ints and sorting by digits is that sorting by ints may take into account a negative sign, and sorting by digits will not. This may be an issue if you used a ‘’ as your separator before the version numbers. Essentially this is a shortcut for a number type of int and the signed option of False:
>>> a = ['ver2.9.9a', 'ver1.11', 'ver2.9.9b', 'ver1.11.4', 'ver1.10.1'] >>> natsorted(a, number_type=int) ['ver2.9.9a', 'ver2.9.9b', 'ver1.10.1', 'ver1.11', 'ver1.11.4'] >>> natsorted(a, number_type=None) ['ver1.10.1', 'ver1.11', 'ver1.11.4', 'ver2.9.9a', 'ver2.9.9b']
The versorted function is simply a wrapper for number_type=None, and if you need to sort just version numbers it is best to use the versorted function for clarity:
>>> natsorted(a, number_type=None) == versorted(a) True
Using a sorting key
Like the builtin sorted function, natsorted can accept a key so that you can sort based on a particular item of a list or by an attribute of a class:
>>> from operator import attrgetter, itemgetter >>> a = [['num4', 'b'], ['num8', 'c'], ['num2', 'a']] >>> natsorted(a, key=itemgetter(0)) [['num2', 'a'], ['num4', 'b'], ['num8', 'c']] >>> class Foo: ... def __init__(self, bar): ... self.bar = bar ... def __repr__(self): ... return "Foo('{0}')".format(self.bar) >>> b = [Foo('num3'), Foo('num5'), Foo('num2')] >>> natsorted(b, key=attrgetter('bar')) [Foo('num2'), Foo('num3'), Foo('num5')]
API
The natsort package provides five functions: natsort_key, natsorted, versorted, index_natsorted, and index_versorted. You can look at the unit tests to see more thorough examples of how natsort can be used.
natsorted
natsort.natsorted (sequence, key = lambda x: x, number_type = float, signed = True, exp = True)
 sequence (iterable)
 The sequence to sort.
 key (function)
 A key used to determine how to sort each element of the sequence.
 number_type (None, float, int)
 The types of number to sort by: float searches for floating point numbers, int searches for integers, and None searches for digits (like integers but does not take into account negative sign). None is a shortcut for number_type = int and signed = False.
 signed (True, False)
 By default a ‘+’ or ‘’ before a number is taken to be the sign of the number. If signed is False, any ‘+’ or ‘’ will not be considered to be part of the number, but as part of the string.
 exp (True, False)
 This option only applies to number_type = float. If exp = True, a string like "3.5e5" will be interpreted as 350000, i.e. the exponential part is considered to be part of the number. If exp = False, "3.5e5" is interpreted as (3.5, "e", 5). The default behavior is exp = True.
 returns
 The sorted sequence.
Use natsorted just like the builtin sorted:
>>> from natsort import natsorted >>> a = ['num3', 'num5', 'num2'] >>> natsorted(a) ['num2', 'num3', 'num5']
versorted
natsort.versorted (sequence, key = lambda x: x)
 sequence (iterable)
 The sequence to sort.
 key (function)
 A key used to determine how to sort each element of the sequence.
 returns
 The sorted sequence.
Use versorted just like the builtin sorted:
>>> from natsort import versorted >>> a = ['num4.0.2', 'num3.4.1', 'num3.4.2'] >>> versorted(a) ['num3.4.1', 'num3.4.2', 'num4.0.2']
This is a wrapper around natsorted(seq, number_type=None), and is used to easily sort version numbers.
index_natsorted
natsort.index_natsorted (sequence, key = lambda x: x, number_type = float, signed = True, exp = True)
 sequence (iterable)
 The sequence to sort.
 key (function)
 A key used to determine how to sort each element of the sequence.
 number_type (None, float, int)
 The types of number to sort on: float searches for floating point numbers, int searches for integers, and None searches for digits (like integers but does not take into account negative sign). None is a shortcut for number_type = int and signed = False.
 signed (True, False)
 By default a ‘+’ or ‘’ before a number is taken to be the sign of the number. If signed is False, any ‘+’ or ‘’ will not be considered to be part of the number, but as part part of the string.
 exp (True, False)
 This option only applies to number_type = float. If exp = True, a string like "3.5e5" will be interpreted as 350000, i.e. the exponential part is considered to be part of the number. If exp = False, "3.5e5" is interpreted as (3.5, "e", 5). The default behavior is exp = True.
 returns
 The ordered indexes of the sequence.
Use index_natsorted if you want to sort multiple lists by the sort order of one list:
>>> from natsort import index_natsorted >>> a = ['num3', 'num5', 'num2'] >>> b = ['foo', 'bar', 'baz'] >>> index = index_natsorted(a) >>> index [2, 0, 1] >>> # Sort both lists by the sort order of a >>> [a[i] for i in index] ['num2', 'num3', 'num5'] >>> [b[i] for i in index] ['baz', 'foo', 'bar']
index_versorted
natsort.index_versorted (sequence, key = lambda x: x)
 sequence (iterable)
 The sequence to sort.
 key (function)
 A key used to determine how to sort each element of the sequence.
 returns
 The ordered indexes of the sequence.
Use index_versorted just like the builtin sorted:
>>> from natsort import index_versorted >>> a = ['num4.0.2', 'num3.4.1', 'num3.4.2'] >>> index_versorted(a) [1, 2, 0]
This is a wrapper around index_natsorted(seq, number_type=None), and is used to easily sort version numbers by their indexes.
natsort_key
natsort.natsort_key (value, number_type = float, signed = True, exp = True, py3_safe = False)
 value
 The value used by the sorting algorithm
 number_type (None, float, int)
 The types of number to sort on: float searches for floating point numbers, int searches for integers, and None searches for digits (like integers but does not take into account negative sign). None is a shortcut for number_type = int and signed = False.
 signed (True, False)
 By default a ‘+’ or ‘’ before a number is taken to be the sign of the number. If signed is False, any ‘+’ or ‘’ will not be considered to be part of the number, but as part part of the string.
 exp (True, False)
 This option only applies to number_type = float. If exp = True, a string like "3.5e5" will be interpreted as 350000, i.e. the exponential part is considered to be part of the number. If exp = False, "3.5e5" is interpreted as (3.5, "e", 5). The default behavior is exp = True.
 py3_safe (True, False)
 This will make the string parsing algorithm be more careful by placing an empty string between two adjacent numbers after the parsing algorithm. This will prevent the “unorderable types” error.
 returns
 The modified value with numbers extracted.
Using natsort_key is just like any other sorting key in python:
>>> from natsort import natsort_key >>> a = ['num3', 'num5', 'num2'] >>> a.sort(key=natsort_key) >>> a ['num2', 'num3', 'num5']
It works by separating out the numbers from the strings:
>>> natsort_key('num2') ('num', 2.0)
If you need to call natsort_key with the number_type argument, or get a special attribute or item of each element of the sequence, the easiest way is to make a lambda expression that calls natsort_key:
>>> from operator import itemgetter >>> a = [['num4', 'b'], ['num8', 'c'], ['num2', 'a']] >>> f = itemgetter(0) >>> a.sort(key=lambda x: natsort_key(f(x), number_type=int)) >>> a [['num2', 'a'], ['num4', 'b'], ['num8', 'c']]
Shell Script
For your convenience, there is a natsort shell script supplied to you that allows you to call natsort from the commandline. natsort was written to aid in computational chemistry research so that it would be easy to analyze large sets of output files named after the parameter used:
$ ls *.out mode1000.35.out mode1243.34.out mode744.43.out mode943.54.out
(Obviously, in reality there would be more files, but you get the idea.) Notice that the shell sorts in lexicographical order. This is the behavior of programs like find as well as ls. The problem is in passing these files to an analysis program that causes them not to appear in numerical order, which can lead to bad analysis. To remedy this, use natsort:
# This won't get you what you want $ foo *.out # This will sort naturally $ natsort *.out mode744.43.out mode943.54.out mode1000.35.out mode1243.34.out $ natsort *.out  xargs foo
You can also filter out numbers using the natsort commandline script:
$ natsort *.out f 900 1100 # Select only numbers between 9001100 mode943.54.out mode1000.35.out
If needed, you can exclude specific numbers:
$ natsort *.out e 1000.35 # Exclude 1000.35 from search mode744.43.out mode943.54.out mode1243.34.out
For other options, use natsort help. In general, the other options mirror the natsorted API.
It is also helpful to note that natsort accepts pipes.
Note to users of the natsort shell script from < v. 3.1.0
The natsort shell script options and implementation for version 3.1.0 has changed slightly. Options relating to interpreting input as file or directory paths have been removed, and internally the input is no longer treated as file paths. In most situations, this should not give different results, but in some unique cases it may. Feel free to contact me if this ruins your work flow.
History
06282014 v. 3.3.0
 Added a ‘versorted’ method for more convenient sorting of versions.
 Updated commandline tool –number_type option with ‘version’ and ‘ver’ to make it more clear how to sort version numbers.
 Moved unittesting mechanism from being docstringbased to actual unit tests in actual functions.
 This has provided the ability determine the coverage of the unit tests (99%).
 This also makes the pydoc documentation a bit more clear.
 Made docstrings for public functions mirror the README API.
 Connected natsort development to TravisCI to help ensure quality releases.
06202014 v. 3.2.1
 Re“Fixed” unorderable types issue on Python 3.x  this workaround is for when the problem occurs in the middle of the string.
05072014 v. 3.2.0
 “Fixed” unorderable types issue on Python 3.x with a workaround that attempts to replicate the Python 2.x behavior by putting all the numbers (or strings that begin with numbers) first.
 Now explicitly excluding __pycache__ from releases by adding a prune statement to MANIFEST.in.
05052014 v. 3.1.2
 Added setup.cfg to support universal wheels.
 Added Python 3.0 and Python 3.1 as requiring the argparse module.
03012014 v. 3.1.1
 Added ability to sort lists of lists.
 Cleaned up import statements.
01202014 v. 3.1.0
Added the signed and exp options to allow finer tuning of the sorting
Entire codebase now works for both Python 2 and Python 3 without needing to run 2to3.
Updated all doctests.
Further simplified the natsort base code by removing unneeded functions.
Simplified documentation where possible.
Improved the shell script code
 Made the documentation less “path”centric to make it clear it is not just for sorting file paths.
 Removed the filesystembased options because these can be achieved better though a pipeline.
 Added doctests.
 Added new options that correspond to signed and exp.
 The user can now specify multiple numbers to exclude or multiple ranges to filter by.
10012013 v. 3.0.2
 Made float, int, and digit searching algorithms all share the same base function.
 Fixed some outdated comments.
 Made the __version__ variable available when importing the module.
8152013 v. 3.0.1
 Added support for unicode strings.
 Removed extraneous string2int function.
 Fixed empty string removal function.
7132013 v. 3.0.0
 Added a number_type argument to the sorting functions to specify how liberal to be when deciding what a number is.
 Reworked the documentation.
6252013 v. 2.2.0
 Added key attribute to natsorted and index_natsorted so that it mimics the functionality of the builtin sorted
 Added tests to reflect the new functionality, as well as tests demonstrating how to get similar functionality using natsort_key.
1252012 v. 2.1.0
 Reorganized package.
 Now using a platform independent shell script generator (entry_points from distribute).
 Can now execute natsort from command line with python m natsort as well.
11302012 v. 2.0.2
 Added the use_2to3 option to setup.py.
 Added distribute_setup.py to the distribution.
 Added dependency to the argparse module (for python2.6).
11212012 v. 2.0.1
 Reorganized directory structure.
 Added tests into the natsort.py file iteself.
11162012, v. 2.0.0
 Updated sorting algorithm to support floats (including exponentials) and basic version number support.
 Added better README documentation.
 Added doctests.
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