81 lines
2.7 KiB
Python
81 lines
2.7 KiB
Python
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from .bases import _ScandinavianStemmer
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from whoosh.compat import u
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class SwedishStemmer(_ScandinavianStemmer):
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"""
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The Swedish Snowball stemmer.
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:cvar __vowels: The Swedish vowels.
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:type __vowels: unicode
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:cvar __s_ending: Letters that may directly appear before a word final 's'.
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:type __s_ending: unicode
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:cvar __step1_suffixes: Suffixes to be deleted in step 1 of the algorithm.
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:type __step1_suffixes: tuple
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:cvar __step2_suffixes: Suffixes to be deleted in step 2 of the algorithm.
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:type __step2_suffixes: tuple
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:cvar __step3_suffixes: Suffixes to be deleted in step 3 of the algorithm.
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:type __step3_suffixes: tuple
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:note: A detailed description of the Swedish
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stemming algorithm can be found under
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http://snowball.tartarus.org/algorithms/swedish/stemmer.html
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"""
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__vowels = u("aeiouy\xE4\xE5\xF6")
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__s_ending = "bcdfghjklmnoprtvy"
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__step1_suffixes = ("heterna", "hetens", "heter", "heten",
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"anden", "arnas", "ernas", "ornas", "andes",
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"andet", "arens", "arna", "erna", "orna",
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"ande", "arne", "aste", "aren", "ades",
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"erns", "ade", "are", "ern", "ens", "het",
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"ast", "ad", "en", "ar", "er", "or", "as",
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"es", "at", "a", "e", "s")
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__step2_suffixes = ("dd", "gd", "nn", "dt", "gt", "kt", "tt")
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__step3_suffixes = ("fullt", u("l\xF6st"), "els", "lig", "ig")
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def stem(self, word):
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"""
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Stem a Swedish word and return the stemmed form.
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:param word: The word that is stemmed.
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:type word: str or unicode
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:return: The stemmed form.
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:rtype: unicode
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"""
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word = word.lower()
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r1 = self._r1_scandinavian(word, self.__vowels)
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# STEP 1
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for suffix in self.__step1_suffixes:
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if r1.endswith(suffix):
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if suffix == "s":
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if word[-2] in self.__s_ending:
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word = word[:-1]
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r1 = r1[:-1]
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else:
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word = word[:-len(suffix)]
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r1 = r1[:-len(suffix)]
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break
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# STEP 2
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for suffix in self.__step2_suffixes:
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if r1.endswith(suffix):
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word = word[:-1]
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r1 = r1[:-1]
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break
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# STEP 3
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for suffix in self.__step3_suffixes:
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if r1.endswith(suffix):
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if suffix in ("els", "lig", "ig"):
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word = word[:-len(suffix)]
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elif suffix in ("fullt", u("l\xF6st")):
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word = word[:-1]
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break
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return word
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