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whoosh / src / whoosh / lang / snowball / norwegian.py

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from .bases import _ScandinavianStemmer

from whoosh.compat import u


class NorwegianStemmer(_ScandinavianStemmer):

    """
    The Norwegian Snowball stemmer.

    :cvar __vowels: The Norwegian vowels.
    :type __vowels: unicode
    :cvar __s_ending: Letters that may directly appear before a word final 's'.
    :type __s_ending: unicode
    :cvar __step1_suffixes: Suffixes to be deleted in step 1 of the algorithm.
    :type __step1_suffixes: tuple
    :cvar __step2_suffixes: Suffixes to be deleted in step 2 of the algorithm.
    :type __step2_suffixes: tuple
    :cvar __step3_suffixes: Suffixes to be deleted in step 3 of the algorithm.
    :type __step3_suffixes: tuple
    :note: A detailed description of the Norwegian
           stemming algorithm can be found under
           http://snowball.tartarus.org/algorithms/norwegian/stemmer.html

    """

    __vowels = u"aeiouy\xE6\xE5\xF8"
    __s_ending = "bcdfghjlmnoprtvyz"
    __step1_suffixes = ("hetenes", "hetene", "hetens", "heter",
                        "heten", "endes", "ande", "ende", "edes",
                        "enes", "erte", "ede", "ane", "ene", "ens",
                        "ers", "ets", "het", "ast", "ert", "en",
                        "ar", "er", "as", "es", "et", "a", "e", "s")

    __step2_suffixes = ("dt", "vt")

    __step3_suffixes = ("hetslov", "eleg", "elig", "elov", "slov",
                          "leg", "eig", "lig", "els", "lov", "ig")

    def stem(self, word):
        """
        Stem a Norwegian word and return the stemmed form.

        :param word: The word that is stemmed.
        :type word: str or unicode
        :return: The stemmed form.
        :rtype: unicode

        """
        word = word.lower()

        r1 = self._r1_scandinavian(word, self.__vowels)

        # STEP 1
        for suffix in self.__step1_suffixes:
            if r1.endswith(suffix):
                if suffix in ("erte", "ert"):
                    word = "".join((word[:-len(suffix)], "er"))
                    r1 = "".join((r1[:-len(suffix)], "er"))

                elif suffix == "s":
                    if (word[-2] in self.__s_ending or
                        (word[-2] == "k" and word[-3] not in self.__vowels)):
                        word = word[:-1]
                        r1 = r1[:-1]
                else:
                    word = word[:-len(suffix)]
                    r1 = r1[:-len(suffix)]
                break

        # STEP 2
        for suffix in self.__step2_suffixes:
            if r1.endswith(suffix):
                word = word[:-1]
                r1 = r1[:-1]
                break

        # STEP 3
        for suffix in self.__step3_suffixes:
            if r1.endswith(suffix):
                word = word[:-len(suffix)]
                break

        return word