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https://github.com/dzieciou/pystempel

Python port of Stempel, an algorithmic stemmer for Polish language.
https://github.com/dzieciou/pystempel

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Python port of Stempel, an algorithmic stemmer for Polish language.

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README 

        
Stempel Stemmer

===============



.. image:: https://badge.fury.io/py/pystempel.svg

    :target: https://badge.fury.io/py/pystempel



Python port of Stempel, an algorithmic stemmer for the Polish language, originally written in Java.



The original stemmer has been implemented as part of `Egothor Project`_, taken virtually unchanged to

`Stempel Stemmer Java library`_ by Andrzej Białecki and next included as part of `Apache Lucene`_,

a free and open-source search engine library. It is also used by `Elastic Search`_ search engine.



.. _Egothor Project: https://www.egothor.org/product/egothor2/

.. _Stempel Stemmer Java library: http://www.getopt.org/stempel/index.html

.. _Apache Lucene: https://lucene.apache.org/core/3_1_0/api/contrib-stempel/index.html

.. _Elastic Search: https://www.elastic.co/guide/en/elasticsearch/plugins/current/analysis-stempel.html



This package includes also high-quality stemming tables for Polish: the original one pretrained by

Andrzej Białecki on 20,000 training sets, and a new one, pretrained on 259,080 training sets

from `Polimorf dictionary`_ by me.



.. _Polimorf dictionary: https://clarin-pl.eu/dspace/handle/11321/577



The port does not include code for compiling stemming tables.



.. _sjp.pl: https://sjp.pl/slownik/en/



How to use

----------



Install in your local environment:



.. code:: console



  pip install pystempel



Use in your code:



.. code:: python



  >>> from pystempel import Stemmer



    Choose the original (called default) version of a stemmer:



.. code:: python



  >>> stemmer = Stemmer.default()



or a version with a new stemming table pretrained on training sets from Polimorf dictionary:



.. code:: python



 >>> stemmer = Stemmer.polimorf()



Stem:



.. code:: python



  >>> for word in ['książka', 'książki', 'książkami', 'książkowa', 'książkowymi']:

  ...   print(stemmer(word))

  ...

  książek

  książek

  książek

  książkowy

  książkowy



Choosing stemming table

-----------------------



Performance between the original (default) and the new stemming table (Polimorf-based) varies significantly.

The stemmer for the default stemming table is *understemming*, i.e., multiple forms of the

same lemma provide different stems more often (63%) than when using a Polimorf-based stemming table

(13%). However, the file footprint of the latter is bigger (2.2MB vs 0.3MB). Also, loading takes

longer (7.5 seconds vs. 1.3 seconds), though this happens only once when a stemmer is created. Also, 

the stemmer stems slightly faster for the original stemming table: ~60000 vs ~51000 words per second.

See `Evaluation Jupyter Notebook`_ for the detailed evaluation results.



.. _Evaluation Jupyter Notebook: http://htmlpreview.github.io/?https://github.com/dzieciou/pystempel/blob/master/Evaluation.html



Also, please note that the licensing schema of both stemming tables differs, and hence licensing of

data generated with each one. See the "Licensing" section for the details.



Choosing between port and wrapper

---------------------------------



If you work on an NLP project in Python you can choose between Python port and Python wrapper.

Python port is what pystempel tries to achieve: translation from Java implementation to Python.

Python wrapper is what I used in `tests`_: Python functions to call the original Java implementation of

stemmer. You can find more about wrappers and ports in `Stackoverflow comparison post`_. Here, I

compare both approaches to help you decide:



* **Same accuracy**. I have verified the Python port by comparing its output

  with the output of the original Java implementation for 331224 words from the Free Polish dictionary

  (`sjp.pl`_) and for 100% of words, it returns same output.

* **Similar performance**. For the mentioned dataset, both stemmer versions achieved comparable performance.

  Python port completed stemming in 4.4 seconds, while Python wrapper -- in 5 seconds (Intel Core

  i5-6000 3.30 GHz, 16GB RAM, Windows 10, OpenJDK)

* **Different setup**. Python wrapper requires additional installation of Cython and pyjnius.

  Python wrapper will make also `debugging harder`_ (switching between two programming languages).



.. _Stackoverflow comparison post: https://stackoverflow.com/questions/10113218/how-to-decide-when-to-wrap-port-write-from-scratch

.. _debugging harder: https://stackoverflow.com/questions/6970359/find-an-efficient-way-to-integrate-different-language-libraries-into-one-project

.. _tests: tests/



Options

-------



To disable a progress bar when loading stemming tables, set environment variable ``DISABLE_TQDM=True``.



Development setup

-----------------



To set up an environment for development you will need `Anaconda`_ installed.



.. _Anaconda: https://anaconda.org/



.. code:: console



    conda env create --file environment.yml

    conda activate pystempel-env

    pre-commit install



To run tests:



.. code:: console



    curl https://repo1.maven.org/maven2/org/apache/lucene/lucene-analyzers-stempel/8.1.1/lucene-analyzers-stempel-8.1.1.jar > stempel-8.1.1.jar

    pytest ./tests/



To run benchmark:



.. code:: console



    set PYTHONPATH=%PYTHONPATH%;%cd%

    python tests\test_benchmark.py



Licensing

---------



* **Code**: Most of the code is covered by `Egothor`_ Open Source License, an Apache-style license.

  The `Apache License 2.0`_covers the rest of the code. This should be clear from the preamble

  of each file.



* **Data**:



  * The original pretrained stemming table is covered by `Apache License 2.0`_.



  * The new pretrained stemming table is covered by `2-Clause BSD License`_, similarly to the

    `Polimorf dictionary` it has been derived from. The copyright owner of both the stemming table

    and the dictionary is `Institute of Computer Science at Polish Academy of Science`_ (IPI PAN).



  * The Polish dictionary used by the unit tests comes from `sjp.pl`_  and is covered by

    `Apache License 2.0`_ as well.



.. _Egothor: https://www.egothor.org/product/egothor2/

.. _Apache License 2.0: https://www.apache.org/licenses/LICENSE-2.0

.. _Polimorf dictionary: dicts/

.. _2-Clause BSD License: data/polimorf/LICENSE.txt

.. _Institute of Computer Science at Polish Academy of Science: https://ipipan.waw.pl/en/



Alternatives

------------



* `Estem`_ is Erlang wrapper (not port) for Stempel stemmer.

* `pl_stemmer`_ is a Python stemmer based on Porter's Algorithm.

* `polish-stem`_ is a Python stemmer using Finite State Transducers.



.. _Estem: https://github.com/arcusfelis/estem

.. _pl_stemmer: https://github.com/Tutanchamon/pl_stemmer

.. _polish-stem: https://github.com/eugeniashurko/polish-stem