383 lines
17 KiB
Python
383 lines
17 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Natural Language Toolkit: The ISRI Arabic Stemmer
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#
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# Copyright (C) 2001-2012 NLTK Proejct
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# Algorithm: Kazem Taghva, Rania Elkhoury, and Jeffrey Coombs (2005)
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# Author: Hosam Algasaier <hosam_hme@yahoo.com>
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# URL: <http://www.nltk.org/>
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# For license information, see LICENSE.TXT
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"""
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ISRI Arabic Stemmer
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The algorithm for this stemmer is described in:
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Taghva, K., Elkoury, R., and Coombs, J. 2005. Arabic Stemming without a root
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dictionary. Information Science Research Institute. University of Nevada, Las
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Vegas, USA.
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The Information Science Research Institute’s (ISRI) Arabic stemmer shares many
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features with the Khoja stemmer. However, the main difference is that ISRI
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stemmer does not use root dictionary. Also, if a root is not found, ISRI
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stemmer returned normalized form, rather than returning the original
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unmodified word.
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Additional adjustments were made to improve the algorithm:
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1- Adding 60 stop words.
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2- Adding the pattern (تفاعيل) to ISRI pattern set.
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3- The step 2 in the original algorithm was normalizing all hamza. This step is
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discarded because it increases the word ambiguities and changes the original
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root.
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"""
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from __future__ import unicode_literals
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import re
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class ISRIStemmer(object):
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'''
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ISRI Arabic stemmer based on algorithm: Arabic Stemming without a root dictionary.
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Information Science Research Institute. University of Nevada, Las Vegas, USA.
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A few minor modifications have been made to ISRI basic algorithm.
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See the source code of this module for more information.
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isri.stem(token) returns Arabic root for the given token.
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The ISRI Stemmer requires that all tokens have Unicode string types.
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If you use Python IDLE on Arabic Windows you have to decode text first
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using Arabic '1256' coding.
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'''
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def __init__(self):
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self.stm = 'defult none'
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self.p3 = ['\u0643\u0627\u0644', '\u0628\u0627\u0644',
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'\u0648\u0644\u0644', '\u0648\u0627\u0644'] # length three prefixes
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self.p2 = ['\u0627\u0644', '\u0644\u0644'] # length two prefixes
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self.p1 = ['\u0644', '\u0628', '\u0641', '\u0633', '\u0648',
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'\u064a', '\u062a', '\u0646', '\u0627'] # length one prefixes
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self.s3 = ['\u062a\u0645\u0644', '\u0647\u0645\u0644',
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'\u062a\u0627\u0646', '\u062a\u064a\u0646',
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'\u0643\u0645\u0644'] # length three suffixes
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self.s2 = ['\u0648\u0646', '\u0627\u062a', '\u0627\u0646',
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'\u064a\u0646', '\u062a\u0646', '\u0643\u0645',
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'\u0647\u0646', '\u0646\u0627', '\u064a\u0627',
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'\u0647\u0627', '\u062a\u0645', '\u0643\u0646',
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'\u0646\u064a', '\u0648\u0627', '\u0645\u0627',
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'\u0647\u0645'] # length two suffixes
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self.s1 = ['\u0629', '\u0647', '\u064a', '\u0643', '\u062a',
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'\u0627', '\u0646'] # length one suffixes
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self.pr4 = {0: ['\u0645'], 1:['\u0627'],
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2: ['\u0627', '\u0648', '\u064A'], 3:['\u0629']} # groups of length four patterns
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self.pr53 = {0: ['\u0627', '\u062a'],
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1: ['\u0627', '\u064a', '\u0648'],
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2: ['\u0627', '\u062a', '\u0645'],
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3: ['\u0645', '\u064a', '\u062a'],
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4: ['\u0645', '\u062a'],
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5: ['\u0627', '\u0648'],
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6: ['\u0627', '\u0645']} # Groups of length five patterns and length three roots
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self.re_short_vowels = re.compile(r'[\u064B-\u0652]')
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self.re_hamza = re.compile(r'[\u0621\u0624\u0626]')
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self.re_intial_hamza = re.compile(r'^[\u0622\u0623\u0625]')
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self.stop_words = ['\u064a\u0643\u0648\u0646',
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'\u0648\u0644\u064a\u0633',
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'\u0648\u0643\u0627\u0646',
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'\u0643\u0630\u0644\u0643',
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'\u0627\u0644\u062a\u064a',
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'\u0648\u0628\u064a\u0646',
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'\u0639\u0644\u064a\u0647\u0627',
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'\u0645\u0633\u0627\u0621',
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'\u0627\u0644\u0630\u064a',
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'\u0648\u0643\u0627\u0646\u062a',
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'\u0648\u0644\u0643\u0646',
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'\u0648\u0627\u0644\u062a\u064a',
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'\u062a\u0643\u0648\u0646',
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'\u0627\u0644\u064a\u0648\u0645',
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'\u0627\u0644\u0644\u0630\u064a\u0646',
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'\u0639\u0644\u064a\u0647',
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'\u0643\u0627\u0646\u062a',
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'\u0644\u0630\u0644\u0643',
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'\u0623\u0645\u0627\u0645',
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'\u0647\u0646\u0627\u0643',
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'\u0645\u0646\u0647\u0627',
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'\u0645\u0627\u0632\u0627\u0644',
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'\u0644\u0627\u0632\u0627\u0644',
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'\u0644\u0627\u064a\u0632\u0627\u0644',
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'\u0645\u0627\u064a\u0632\u0627\u0644',
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'\u0627\u0635\u0628\u062d',
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'\u0623\u0635\u0628\u062d',
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'\u0623\u0645\u0633\u0649',
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'\u0627\u0645\u0633\u0649',
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'\u0623\u0636\u062d\u0649',
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'\u0627\u0636\u062d\u0649',
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'\u0645\u0627\u0628\u0631\u062d',
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'\u0645\u0627\u0641\u062a\u0626',
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'\u0645\u0627\u0627\u0646\u0641\u0643',
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'\u0644\u0627\u0633\u064a\u0645\u0627',
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'\u0648\u0644\u0627\u064a\u0632\u0627\u0644',
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'\u0627\u0644\u062d\u0627\u0644\u064a',
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'\u0627\u0644\u064a\u0647\u0627',
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'\u0627\u0644\u0630\u064a\u0646',
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'\u0641\u0627\u0646\u0647',
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'\u0648\u0627\u0644\u0630\u064a',
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'\u0648\u0647\u0630\u0627',
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'\u0644\u0647\u0630\u0627',
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'\u0641\u0643\u0627\u0646',
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'\u0633\u062a\u0643\u0648\u0646',
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'\u0627\u0644\u064a\u0647',
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'\u064a\u0645\u0643\u0646',
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'\u0628\u0647\u0630\u0627',
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'\u0627\u0644\u0630\u0649']
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def stem(self, token):
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"""
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Stemming a word token using the ISRI stemmer.
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"""
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self.stm = token
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self.norm(1) # remove diacritics which representing Arabic short vowels
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if self.stm in self.stop_words: return self.stm # exclude stop words from being processed
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self.pre32() # remove length three and length two prefixes in this order
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self.suf32() # remove length three and length two suffixes in this order
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self.waw() # remove connective ‘و’ if it precedes a word beginning with ‘و’
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self.norm(2) # normalize initial hamza to bare alif
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if len(self.stm) <= 3: return self.stm # return stem if less than or equal to three
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if len(self.stm) == 4: # length 4 word
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self.pro_w4()
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return self.stm
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elif len(self.stm) == 5: # length 5 word
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self.pro_w53()
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self.end_w5()
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return self.stm
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elif len(self.stm) == 6: # length 6 word
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self.pro_w6()
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self.end_w6()
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return self.stm
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elif len(self.stm) == 7: # length 7 word
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self.suf1()
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if len(self.stm) == 7:
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self.pre1()
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if len(self.stm) == 6:
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self.pro_w6()
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self.end_w6()
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return self.stm
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return self.stm # if word length >7 , then no stemming
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def norm(self, num):
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"""
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normalization:
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num=1 normalize diacritics
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num=2 normalize initial hamza
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num=3 both 1&2
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"""
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self.k = num
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if self.k == 1:
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self.stm = self.re_short_vowels.sub('', self.stm)
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return self.stm
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elif self.k == 2:
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self.stm = self.re_intial_hamza.sub(r'\u0627', self.stm)
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return self.stm
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elif self.k == 3:
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self.stm = self.re_short_vowels.sub('', self.stm)
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self.stm = self.re_intial_hamza.sub(r'\u0627', self.stm)
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return self.stm
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def pre32(self):
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"""remove length three and length two prefixes in this order"""
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if len(self.stm) >= 6:
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for pre3 in self.p3:
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if self.stm.startswith(pre3):
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self.stm = self.stm[3:]
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return self.stm
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elif len(self.stm) >= 5:
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for pre2 in self.p2:
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if self.stm.startswith(pre2):
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self.stm = self.stm[2:]
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return self.stm
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def suf32(self):
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"""remove length three and length two suffixes in this order"""
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if len(self.stm) >= 6:
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for suf3 in self.s3:
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if self.stm.endswith(suf3):
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self.stm = self.stm[:-3]
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return self.stm
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elif len(self.stm) >= 5:
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for suf2 in self.s2:
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if self.stm.endswith(suf2):
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self.stm = self.stm[:-2]
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return self.stm
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def waw(self):
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"""remove connective ‘و’ if it precedes a word beginning with ‘و’ """
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if (len(self.stm) >= 4) & (self.stm[:2] == '\u0648\u0648'):
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self.stm = self.stm[1:]
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return self.stm
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def pro_w4(self):
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"""process length four patterns and extract length three roots"""
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if self.stm[0] in self.pr4[0]: # مفعل
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self.stm = self.stm[1:]
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return self.stm
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elif self.stm[1] in self.pr4[1]: # فاعل
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self.stm = self.stm[0] + self.stm[2:]
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return self.stm
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elif self.stm[2] in self.pr4[2]: # فعال - فعول - فعيل
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self.stm = self.stm[:2] + self.stm[3]
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return self.stm
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elif self.stm[3] in self.pr4[3]: # فعلة
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self.stm = self.stm[:-1]
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return self.stm
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else:
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self.suf1() # do - normalize short sufix
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if len(self.stm) == 4:
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self.pre1() # do - normalize short prefix
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return self.stm
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def pro_w53(self):
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"""process length five patterns and extract length three roots"""
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if ((self.stm[2] in self.pr53[0]) & (self.stm[0] == '\u0627')): # افتعل - افاعل
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self.stm = self.stm[1] + self.stm[3:]
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return self.stm
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elif ((self.stm[3] in self.pr53[1]) & (self.stm[0] == '\u0645')): # مفعول - مفعال - مفعيل
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self.stm = self.stm[1:3] + self.stm[4]
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return self.stm
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elif ((self.stm[0] in self.pr53[2]) & (self.stm[4] == '\u0629')): # مفعلة - تفعلة - افعلة
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self.stm = self.stm[1:4]
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return self.stm
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elif ((self.stm[0] in self.pr53[3]) & (self.stm[2] == '\u062a')): # مفتعل - يفتعل - تفتعل
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self.stm = self.stm[1] + self.stm[3:]
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return self.stm
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elif ((self.stm[0] in self.pr53[4]) & (self.stm[2] == '\u0627')): #مفاعل - تفاعل
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self.stm = self.stm[1] + self.stm[3:]
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return self.stm
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elif ((self.stm[2] in self.pr53[5]) & (self.stm[4] == '\u0629')): # فعولة - فعالة
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self.stm = self.stm[:2] + self.stm[3]
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return self.stm
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elif ((self.stm[0] in self.pr53[6]) & (self.stm[1] == '\u0646')): # انفعل - منفعل
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self.stm = self.stm[2:]
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return self.stm
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elif ((self.stm[3] == '\u0627') & (self.stm[0] == '\u0627')): # افعال
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self.stm = self.stm[1:3] + self.stm[4]
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return self.stm
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elif ((self.stm[4] == '\u0646') & (self.stm[3] == '\u0627')): # فعلان
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self.stm = self.stm[:3]
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return self.stm
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elif ((self.stm[3] == '\u064a') & (self.stm[0] == '\u062a')): # تفعيل
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self.stm = self.stm[1:3] + self.stm[4]
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return self.stm
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elif ((self.stm[3] == '\u0648') & (self.stm[1] == '\u0627')): # فاعول
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self.stm = self.stm[0] + self.stm[2] + self.stm[4]
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return self.stm
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elif ((self.stm[2] == '\u0627') & (self.stm[1] == '\u0648')): # فواعل
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self.stm = self.stm[0] + self.stm[3:]
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return self.stm
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elif ((self.stm[3] == '\u0626') & (self.stm[2] == '\u0627')): # فعائل
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self.stm = self.stm[:2] + self.stm[4]
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return self.stm
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elif ((self.stm[4] == '\u0629') & (self.stm[1] == '\u0627')): # فاعلة
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self.stm = self.stm[0] + self.stm[2:4]
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return self.stm
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elif ((self.stm[4] == '\u064a') & (self.stm[2] == '\u0627')): # فعالي
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self.stm = self.stm[:2] + self.stm[3]
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return self.stm
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else:
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self.suf1() # do - normalize short sufix
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if len(self.stm) == 5:
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self.pre1() # do - normalize short prefix
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return self.stm
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def pro_w54(self):
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"""process length five patterns and extract length four roots"""
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if (self.stm[0] in self.pr53[2]): #تفعلل - افعلل - مفعلل
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self.stm = self.stm[1:]
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return self.stm
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elif (self.stm[4] == '\u0629'): # فعللة
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self.stm = self.stm[:4]
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return self.stm
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elif (self.stm[2] == '\u0627'): # فعالل
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self.stm = self.stm[:2] + self.stm[3:]
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return self.stm
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def end_w5(self):
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"""ending step (word of length five)"""
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if len(self.stm) == 3:
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return self.stm
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elif len(self.stm) == 4:
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self.pro_w4()
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return self.stm
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elif len(self.stm) == 5:
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self.pro_w54()
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return self.stm
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def pro_w6(self):
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"""process length six patterns and extract length three roots"""
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if ((self.stm.startswith('\u0627\u0633\u062a')) or (self.stm.startswith('\u0645\u0633\u062a'))): # مستفعل - استفعل
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self.stm = self.stm[3:]
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return self.stm
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elif (self.stm[0] == '\u0645' and self.stm[3] == '\u0627' and self.stm[5] == '\u0629'): # مفعالة
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self.stm = self.stm[1:3] + self.stm[4]
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return self.stm
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elif (self.stm[0] == '\u0627' and self.stm[2] == '\u062a' and self.stm[4] == '\u0627'): # افتعال
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self.stm = self.stm[1] + self.stm[3] + self.stm[5]
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return self.stm
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elif (self.stm[0] == '\u0627' and self.stm[3] == '\u0648' and self.stm[2] == self.stm[4]): # افعوعل
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self.stm = self.stm[1] + self.stm[4:]
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return self.stm
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elif (self.stm[0] == '\u062a' and self.stm[2] == '\u0627' and self.stm[4] == '\u064a'): # تفاعيل new pattern
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self.stm = self.stm[1] + self.stm[3] + self.stm[5]
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return self.stm
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else:
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self.suf1() # do - normalize short sufix
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if len(self.stm) == 6:
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self.pre1() # do - normalize short prefix
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return self.stm
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def pro_w64(self):
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"""process length six patterns and extract length four roots"""
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if (self.stm[0] and self.stm[4]) == '\u0627': # افعلال
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self.stm = self.stm[1:4] + self.stm[5]
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return self.stm
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elif (self.stm.startswith('\u0645\u062a')): # متفعلل
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self.stm = self.stm[2:]
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return self.stm
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def end_w6(self):
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"""ending step (word of length six)"""
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if len(self.stm) == 3:
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return self.stm
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elif len(self.stm) == 5:
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self.pro_w53()
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self.end_w5()
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return self.stm
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elif len (self.stm) == 6:
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self.pro_w64()
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return self.stm
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def suf1(self):
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"""normalize short sufix"""
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for sf1 in self.s1:
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if self.stm.endswith(sf1):
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self.stm = self.stm[:-1]
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return self.stm
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def pre1(self):
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"""normalize short prefix"""
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for sp1 in self.p1:
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if self.stm.startswith(sp1):
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self.stm = self.stm[1:]
|
||
return self.stm
|