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 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 setup environment for development you will need poetry
_ 1.4.0 or higher installed.
.. _poetry: https://python-poetry.org/
.. code:: console
poetry install
poetry shell
pre-commit install
To run tests download original stemmer in Java:
.. 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
and run:
.. code:: console
poetry run pytest
To run performance benchmark:
.. code:: console
PYTHONPATH=$PWD poetry run python tests/test_benchmark.py
Licensing
.. _Egothor: https://www.egothor.org/product/egothor2/
.. _Apache License 2.0: https://www.apache.org/licenses/LICENSE-2.0
.. _Polimorf dictionary copy: 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
Release notes
2.0.0: API backward incompatible changes
- Refactor
stempel
to pystempel
package (#26) - Refactor
StempelStemmer
to Stemmer
and Stemmer.stem
to callable (#26)
1.2.0: Stable version