397 lines
15 KiB
Python
397 lines
15 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) 2001-2019 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://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 dictionary.
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Information Science Research Institute. University of Nevada, Las Vegas, USA.
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The Information Science Research Institute’s (ISRI) Arabic stemmer shares many features
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with the Khoja stemmer. However, the main difference is that ISRI stemmer does not use root
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dictionary. Also, if a root is not found, ISRI stemmer returned normalized form, rather than
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returning the original 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 discarded because it
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increases the word ambiguities and changes the original root.
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"""
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import re
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from nltk.stem.api import StemmerI
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class ISRIStemmer(StemmerI):
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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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# length three prefixes
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self.p3 = [
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"\u0643\u0627\u0644",
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"\u0628\u0627\u0644",
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"\u0648\u0644\u0644",
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"\u0648\u0627\u0644",
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]
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# length two prefixes
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self.p2 = ["\u0627\u0644", "\u0644\u0644"]
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# length one prefixes
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self.p1 = [
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"\u0644",
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"\u0628",
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"\u0641",
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"\u0633",
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"\u0648",
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"\u064a",
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"\u062a",
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"\u0646",
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"\u0627",
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]
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# length three suffixes
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self.s3 = [
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"\u062a\u0645\u0644",
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"\u0647\u0645\u0644",
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"\u062a\u0627\u0646",
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"\u062a\u064a\u0646",
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"\u0643\u0645\u0644",
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]
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# length two suffixes
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self.s2 = [
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"\u0648\u0646",
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"\u0627\u062a",
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"\u0627\u0646",
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"\u064a\u0646",
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"\u062a\u0646",
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"\u0643\u0645",
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"\u0647\u0646",
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"\u0646\u0627",
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"\u064a\u0627",
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"\u0647\u0627",
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"\u062a\u0645",
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"\u0643\u0646",
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"\u0646\u064a",
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"\u0648\u0627",
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"\u0645\u0627",
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"\u0647\u0645",
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]
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# length one suffixes
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self.s1 = ["\u0629", "\u0647", "\u064a", "\u0643", "\u062a", "\u0627", "\u0646"]
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# groups of length four patterns
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self.pr4 = {
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0: ["\u0645"],
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1: ["\u0627"],
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2: ["\u0627", "\u0648", "\u064A"],
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3: ["\u0629"],
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}
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# Groups of length five patterns and length three roots
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self.pr53 = {
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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"],
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}
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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_initial_hamza = re.compile(r"^[\u0622\u0623\u0625]")
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self.stop_words = [
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"\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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]
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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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token = self.norm(
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token, 1
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) # remove diacritics which representing Arabic short vowels
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if token in self.stop_words:
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return token # exclude stop words from being processed
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token = self.pre32(
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token
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) # remove length three and length two prefixes in this order
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token = self.suf32(
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token
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) # remove length three and length two suffixes in this order
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token = self.waw(
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token
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) # remove connective ‘و’ if it precedes a word beginning with ‘و’
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token = self.norm(token, 2) # normalize initial hamza to bare alif
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# if 4 <= word length <= 7, then stem; otherwise, no stemming
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if len(token) == 4: # length 4 word
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token = self.pro_w4(token)
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elif len(token) == 5: # length 5 word
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token = self.pro_w53(token)
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token = self.end_w5(token)
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elif len(token) == 6: # length 6 word
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token = self.pro_w6(token)
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token = self.end_w6(token)
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elif len(token) == 7: # length 7 word
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token = self.suf1(token)
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if len(token) == 7:
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token = self.pre1(token)
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if len(token) == 6:
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token = self.pro_w6(token)
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token = self.end_w6(token)
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return token
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def norm(self, word, num=3):
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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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if num == 1:
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word = self.re_short_vowels.sub("", word)
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elif num == 2:
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word = self.re_initial_hamza.sub("\u0627", word)
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elif num == 3:
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word = self.re_short_vowels.sub("", word)
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word = self.re_initial_hamza.sub("\u0627", word)
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return word
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def pre32(self, word):
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"""remove length three and length two prefixes in this order"""
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if len(word) >= 6:
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for pre3 in self.p3:
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if word.startswith(pre3):
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return word[3:]
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if len(word) >= 5:
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for pre2 in self.p2:
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if word.startswith(pre2):
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return word[2:]
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return word
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def suf32(self, word):
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"""remove length three and length two suffixes in this order"""
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if len(word) >= 6:
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for suf3 in self.s3:
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if word.endswith(suf3):
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return word[:-3]
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if len(word) >= 5:
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for suf2 in self.s2:
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if word.endswith(suf2):
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return word[:-2]
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return word
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def waw(self, word):
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"""remove connective ‘و’ if it precedes a word beginning with ‘و’ """
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if len(word) >= 4 and word[:2] == "\u0648\u0648":
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word = word[1:]
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return word
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def pro_w4(self, word):
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"""process length four patterns and extract length three roots"""
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if word[0] in self.pr4[0]: # مفعل
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word = word[1:]
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elif word[1] in self.pr4[1]: # فاعل
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word = word[:1] + word[2:]
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elif word[2] in self.pr4[2]: # فعال - فعول - فعيل
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word = word[:2] + word[3]
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elif word[3] in self.pr4[3]: # فعلة
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word = word[:-1]
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else:
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word = self.suf1(word) # do - normalize short sufix
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if len(word) == 4:
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word = self.pre1(word) # do - normalize short prefix
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return word
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def pro_w53(self, word):
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"""process length five patterns and extract length three roots"""
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if word[2] in self.pr53[0] and word[0] == "\u0627": # افتعل - افاعل
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word = word[1] + word[3:]
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elif word[3] in self.pr53[1] and word[0] == "\u0645": # مفعول - مفعال - مفعيل
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word = word[1:3] + word[4]
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elif word[0] in self.pr53[2] and word[4] == "\u0629": # مفعلة - تفعلة - افعلة
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word = word[1:4]
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elif word[0] in self.pr53[3] and word[2] == "\u062a": # مفتعل - يفتعل - تفتعل
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word = word[1] + word[3:]
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elif word[0] in self.pr53[4] and word[2] == "\u0627": # مفاعل - تفاعل
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word = word[1] + word[3:]
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elif word[2] in self.pr53[5] and word[4] == "\u0629": # فعولة - فعالة
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word = word[:2] + word[3]
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elif word[0] in self.pr53[6] and word[1] == "\u0646": # انفعل - منفعل
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word = word[2:]
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elif word[3] == "\u0627" and word[0] == "\u0627": # افعال
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word = word[1:3] + word[4]
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elif word[4] == "\u0646" and word[3] == "\u0627": # فعلان
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word = word[:3]
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elif word[3] == "\u064a" and word[0] == "\u062a": # تفعيل
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word = word[1:3] + word[4]
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elif word[3] == "\u0648" and word[1] == "\u0627": # فاعول
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word = word[0] + word[2] + word[4]
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elif word[2] == "\u0627" and word[1] == "\u0648": # فواعل
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word = word[0] + word[3:]
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elif word[3] == "\u0626" and word[2] == "\u0627": # فعائل
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word = word[:2] + word[4]
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elif word[4] == "\u0629" and word[1] == "\u0627": # فاعلة
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word = word[0] + word[2:4]
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elif word[4] == "\u064a" and word[2] == "\u0627": # فعالي
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word = word[:2] + word[3]
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else:
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word = self.suf1(word) # do - normalize short sufix
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if len(word) == 5:
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word = self.pre1(word) # do - normalize short prefix
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return word
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def pro_w54(self, word):
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"""process length five patterns and extract length four roots"""
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if word[0] in self.pr53[2]: # تفعلل - افعلل - مفعلل
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word = word[1:]
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elif word[4] == "\u0629": # فعللة
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word = word[:4]
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elif word[2] == "\u0627": # فعالل
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word = word[:2] + word[3:]
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return word
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def end_w5(self, word):
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"""ending step (word of length five)"""
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if len(word) == 4:
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word = self.pro_w4(word)
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elif len(word) == 5:
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word = self.pro_w54(word)
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return word
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def pro_w6(self, word):
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"""process length six patterns and extract length three roots"""
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if word.startswith("\u0627\u0633\u062a") or word.startswith(
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"\u0645\u0633\u062a"
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): # مستفعل - استفعل
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word = word[3:]
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elif (
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word[0] == "\u0645" and word[3] == "\u0627" and word[5] == "\u0629"
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): # مفعالة
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word = word[1:3] + word[4]
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elif (
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word[0] == "\u0627" and word[2] == "\u062a" and word[4] == "\u0627"
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): # افتعال
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word = word[1] + word[3] + word[5]
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elif (
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word[0] == "\u0627" and word[3] == "\u0648" and word[2] == word[4]
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): # افعوعل
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word = word[1] + word[4:]
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elif (
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word[0] == "\u062a" and word[2] == "\u0627" and word[4] == "\u064a"
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): # تفاعيل new pattern
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word = word[1] + word[3] + word[5]
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else:
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word = self.suf1(word) # do - normalize short sufix
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if len(word) == 6:
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word = self.pre1(word) # do - normalize short prefix
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return word
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def pro_w64(self, word):
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"""process length six patterns and extract length four roots"""
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if word[0] == "\u0627" and word[4] == "\u0627": # افعلال
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word = word[1:4] + word[5]
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elif word.startswith("\u0645\u062a"): # متفعلل
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word = word[2:]
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return word
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def end_w6(self, word):
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"""ending step (word of length six)"""
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if len(word) == 5:
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word = self.pro_w53(word)
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word = self.end_w5(word)
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elif len(word) == 6:
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word = self.pro_w64(word)
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return word
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def suf1(self, word):
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"""normalize short sufix"""
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for sf1 in self.s1:
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if word.endswith(sf1):
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return word[:-1]
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return word
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def pre1(self, word):
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"""normalize short prefix"""
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for sp1 in self.p1:
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if word.startswith(sp1):
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return word[1:]
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return word
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