Polyleven -- Fast Pythonic Levenshtein Library

License:	MIT License

1. Introduction

polyleven is a Pythonic Levenshtein distance library that:

• Is fast independent of input types, and hence can be used for both short (like English words) and long input types (like DNA sequences).
• Is stand-alone depending only on core Python packages (such as setuptools for installation).
• Can be used readily in a manner not covered by restrictive licenses such as GPL, hence can be used freely in private codes.

2. How to install

The official package is available on PyPI:

$ pip install polyleven

3. How to use

Polyleven provides a single interface function levenshtein(). You can use this function to measure the similarity of two strings.

>>> from polyleven import levenshtein
>>> levenshtein('aaa', 'ccc')
3

If you only care about distances under a certain threshold, you can pass the max threshold to the third argument.

>>> levenshtein('acc', 'ccc', 1)
1
>>> levenshtein('aaa', 'ccc', 1)
2

In general, you can gain a noticeable speed boost with threshold k < 3.

4. Benchmark

4.1 English Words

To compare Polyleven with other Pythonic edit distance libraries, a million word pairs was generated from SCOWL.

Each library was measured how long it takes to evaluate all of these words. The following table summarises the result:

Function Name	TIME[sec]	SPEED[pairs/s]
edlib	4.763	208216
editdistance	1.943	510450
jellyfish.levenshtein_distance	0.722	1374081
distance.levenshtein	0.623	1591396
Levenshtein.distance	0.500	1982764
polyleven.levenshtein	0.431	2303420

4.2. Longer Inputs

To evaluate the efficiency for longer inputs, I created 5000 pairs of random strings of size 16, 32, 64, 128, 256, 512 and 1024.

Each library was measured how fast it can process these entries. [1]

Library	N=16	N=32	N=64	N=128	N=256	N=512	N=1024
edlib	0.040	0.063	0.094	0.205	0.432	0.908	2.089
editdistance	0.027	0.049	0.086	0.178	0.336	0.740	58.139
jellyfish	0.009	0.032	0.118	0.470	1.874	8.877	42.848
distance	0.007	0.029	0.109	0.431	1.726	6.950	27.998
Levenshtein	0.006	0.022	0.085	0.336	1.328	5.286	21.097
polyleven	0.003	0.005	0.010	0.043	0.149	0.550	2.109

3.3. List of Libraries

Library	Version	URL
edlib	v1.2.1	https://github.com/Martinsos/edlib
editdistance	v0.4	https://github.com/aflc/editdistance
jellyfish	v0.5.6	https://github.com/jamesturk/jellyfish
distance	v0.1.3	https://github.com/doukremt/distance
Levenshtein	v0.12	https://github.com/ztane/python-Levenshtein
polyleven	v0.3	https://github.com/fujimotos/polyleven

[1]	Measured using Python 3.5.3 on Debian Jessie with Intel Core i3-4010U (1.70GHz)