abydos/stemmer/_snowball.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.
Snowball Stemmer base class
"""
from typing import Iterable, Optional, cast
from ._stemmer import _Stemmer
__all__ = ['_Snowball']
class _Snowball(_Stemmer):
"""Snowball stemmer base class.
.. versionadded:: 0.3.6
"""
_vowels = set('aeiouy')
_codanonvowels = set("'bcdfghjklmnpqrstvz")
def _sb_r1(
self, term: str, r1_prefixes: Optional[Iterable[str]] = None
) -> int:
"""Return the R1 region, as defined in the Porter2 specification.
Parameters
----------
term : str
The term to examine
r1_prefixes : iterable
Prefixes to consider
Returns
-------
int
Length of the R1 region
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
vowel_found = False
if hasattr(r1_prefixes, '__iter__'):
for prefix in cast(Iterable[str], r1_prefixes):
if term[: len(prefix)] == prefix:
return len(prefix)
for i in range(len(term)):
if not vowel_found and term[i] in self._vowels:
vowel_found = True
elif vowel_found and term[i] not in self._vowels:
return i + 1
return len(term)
def _sb_r2(
self, term: str, r1_prefixes: Optional[Iterable[str]] = None
) -> int:
"""Return the R2 region, as defined in the Porter2 specification.
Parameters
----------
term : str
The term to examine
r1_prefixes : iterable
Prefixes to consider
Returns
-------
int
Length of the R1 region
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
r1_start = self._sb_r1(term, r1_prefixes)
return r1_start + self._sb_r1(term[r1_start:])
def _sb_ends_in_short_syllable(self, term: str) -> bool:
"""Return True iff term ends in a short syllable.
(...according to the Porter2 specification.)
NB: This is akin to the CVC test from the Porter stemmer. The
description is unfortunately poor/ambiguous.
Parameters
----------
term : str
The term to examine
Returns
-------
bool
True iff term ends in a short syllable
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
if not term:
return False
if len(term) == 2:
if term[-2] in self._vowels and term[-1] not in self._vowels:
return True
elif len(term) >= 3:
if (
term[-3] not in self._vowels
and term[-2] in self._vowels
and term[-1] in self._codanonvowels
):
return True
return False
def _sb_short_word(
self, term: str, r1_prefixes: Optional[Iterable[str]] = None
) -> bool:
"""Return True iff term is a short word.
(...according to the Porter2 specification.)
Parameters
----------
term : str
The term to examine
r1_prefixes : set
Prefixes to consider
Returns
-------
bool
True iff term is a short word
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
if self._sb_r1(term, r1_prefixes) == len(
term
) and self._sb_ends_in_short_syllable(term):
return True
return False
def _sb_has_vowel(self, term: str) -> bool:
"""Return Porter helper function _sb_has_vowel value.
Parameters
----------
term : str
The term to examine
Returns
-------
bool
True iff a vowel exists in the term (as defined in the Porter
stemmer definition)
.. versionadded:: 0.1.0
.. versionchanged:: 0.3.6
Encapsulated in class
"""
for letter in term:
if letter in self._vowels:
return True
return False
if __name__ == '__main__':
import doctest
doctest.testmod()