abydos/stemmer/_snowball_danish.py
# Copyright 2014-2020 by Christopher C. Little.
# This file is part of Abydos.
#
# Abydos is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Abydos is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Abydos. If not, see <http://www.gnu.org/licenses/>.
"""abydos.stemmer._snowball_danish.
Snowball Danish stemmer
"""
from unicodedata import normalize
from ._snowball import _Snowball
__all__ = ['SnowballDanish']
class SnowballDanish(_Snowball):
"""Snowball Danish stemmer.
The Snowball Danish stemmer is defined at:
http://snowball.tartarus.org/algorithms/danish/stemmer.html
.. versionadded:: 0.3.6
"""
_vowels = {'a', 'e', 'i', 'o', 'u', 'y', 'å', 'æ', 'ø'}
_s_endings = {
'a',
'b',
'c',
'd',
'f',
'g',
'h',
'j',
'k',
'l',
'm',
'n',
'o',
'p',
'r',
't',
'v',
'y',
'z',
'å',
}
def stem(self, word: str) -> str:
"""Return Snowball Danish stem.
Parameters
----------
word : str
The word to stem
Returns
-------
str
Word stem
Examples
--------
>>> stmr = SnowballDanish()
>>> stmr.stem('underviser')
'undervis'
>>> stmr.stem('suspension')
'suspension'
>>> stmr.stem('sikkerhed')
'sikker'
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
# lowercase, normalize, and compose
word = normalize('NFC', word.lower())
r1_start = min(max(3, self._sb_r1(word)), len(word))
# Step 1
_r1 = word[r1_start:]
if _r1[-7:] == 'erendes':
word = word[:-7]
elif _r1[-6:] in {'erende', 'hedens'}:
word = word[:-6]
elif _r1[-5:] in {
'ethed',
'erede',
'heden',
'heder',
'endes',
'ernes',
'erens',
'erets',
}:
word = word[:-5]
elif _r1[-4:] in {
'ered',
'ende',
'erne',
'eren',
'erer',
'heds',
'enes',
'eres',
'eret',
}:
word = word[:-4]
elif _r1[-3:] in {'hed', 'ene', 'ere', 'ens', 'ers', 'ets'}:
word = word[:-3]
elif _r1[-2:] in {'en', 'er', 'es', 'et'}:
word = word[:-2]
elif _r1[-1:] == 'e':
word = word[:-1]
elif _r1[-1:] == 's':
if len(word) > 1 and word[-2] in self._s_endings:
word = word[:-1]
# Step 2
if word[r1_start:][-2:] in {'gd', 'dt', 'gt', 'kt'}:
word = word[:-1]
# Step 3
if word[-4:] == 'igst':
word = word[:-2]
_r1 = word[r1_start:]
repeat_step2 = False
if _r1[-4:] == 'elig':
word = word[:-4]
repeat_step2 = True
elif _r1[-4:] == 'løst':
word = word[:-1]
elif _r1[-3:] in {'lig', 'els'}:
word = word[:-3]
repeat_step2 = True
elif _r1[-2:] == 'ig':
word = word[:-2]
repeat_step2 = True
if repeat_step2:
if word[r1_start:][-2:] in {'gd', 'dt', 'gt', 'kt'}:
word = word[:-1]
# Step 4
if (
len(word[r1_start:]) >= 1
and len(word) >= 2
and word[-1] == word[-2]
and word[-1] not in self._vowels
):
word = word[:-1]
return word
if __name__ == '__main__':
import doctest
doctest.testmod()