2026-1-6

venv/Lib/site-packages/whoosh/lang/snowball/german.py

@@ -0,0 +1,144 @@
+from .bases import _StandardStemmer
+
+from whoosh.compat import u
+
+
+class GermanStemmer(_StandardStemmer):
+
+    """
+    The German Snowball stemmer.
+
+    :cvar __vowels: The German vowels.
+    :type __vowels: unicode
+    :cvar __s_ending: Letters that may directly appear before a word final 's'.
+    :type __s_ending: unicode
+    :cvar __st_ending: Letter that may directly appear before a word final 'st'.
+    :type __st_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 German
+           stemming algorithm can be found under
+           http://snowball.tartarus.org/algorithms/german/stemmer.html
+
+    """
+
+    __vowels = u("aeiouy\xE4\xF6\xFC")
+    __s_ending = "bdfghklmnrt"
+    __st_ending = "bdfghklmnt"
+
+    __step1_suffixes = ("ern", "em", "er", "en", "es", "e", "s")
+    __step2_suffixes = ("est", "en", "er", "st")
+    __step3_suffixes = ("isch", "lich", "heit", "keit",
+                          "end", "ung", "ig", "ik")
+
+    def stem(self, word):
+        """
+        Stem a German 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()
+
+        word = word.replace(u("\xDF"), "ss")
+
+        # Every occurrence of 'u' and 'y'
+        # between vowels is put into upper case.
+        for i in range(1, len(word) - 1):
+            if word[i - 1] in self.__vowels and word[i + 1] in self.__vowels:
+                if word[i] == "u":
+                    word = "".join((word[:i], "U", word[i + 1:]))
+
+                elif word[i] == "y":
+                    word = "".join((word[:i], "Y", word[i + 1:]))
+
+        r1, r2 = self._r1r2_standard(word, self.__vowels)
+
+        # R1 is adjusted so that the region before it
+        # contains at least 3 letters.
+        for i in range(1, len(word)):
+            if word[i] not in self.__vowels and word[i - 1] in self.__vowels:
+                if len(word[:i + 1]) < 3 and len(word[:i + 1]) > 0:
+                    r1 = word[3:]
+                elif len(word[:i + 1]) == 0:
+                    return word
+                break
+
+        # STEP 1
+        for suffix in self.__step1_suffixes:
+            if r1.endswith(suffix):
+                if (suffix in ("en", "es", "e") and
+                    word[-len(suffix) - 4:-len(suffix)] == "niss"):
+                    word = word[:-len(suffix) - 1]
+                    r1 = r1[:-len(suffix) - 1]
+                    r2 = r2[:-len(suffix) - 1]
+
+                elif suffix == "s":
+                    if word[-2] in self.__s_ending:
+                        word = word[:-1]
+                        r1 = r1[:-1]
+                        r2 = r2[:-1]
+                else:
+                    word = word[:-len(suffix)]
+                    r1 = r1[:-len(suffix)]
+                    r2 = r2[:-len(suffix)]
+                break
+
+        # STEP 2
+        for suffix in self.__step2_suffixes:
+            if r1.endswith(suffix):
+                if suffix == "st":
+                    if word[-3] in self.__st_ending and len(word[:-3]) >= 3:
+                        word = word[:-2]
+                        r1 = r1[:-2]
+                        r2 = r2[:-2]
+                else:
+                    word = word[:-len(suffix)]
+                    r1 = r1[:-len(suffix)]
+                    r2 = r2[:-len(suffix)]
+                break
+
+        # STEP 3: Derivational suffixes
+        for suffix in self.__step3_suffixes:
+            if r2.endswith(suffix):
+                if suffix in ("end", "ung"):
+                    if ("ig" in r2[-len(suffix) - 2:-len(suffix)] and
+                        "e" not in r2[-len(suffix) - 3:-len(suffix) - 2]):
+                        word = word[:-len(suffix) - 2]
+                    else:
+                        word = word[:-len(suffix)]
+
+                elif (suffix in ("ig", "ik", "isch") and
+                      "e" not in r2[-len(suffix) - 1:-len(suffix)]):
+                    word = word[:-len(suffix)]
+
+                elif suffix in ("lich", "heit"):
+                    if ("er" in r1[-len(suffix) - 2:-len(suffix)] or
+                        "en" in r1[-len(suffix) - 2:-len(suffix)]):
+                        word = word[:-len(suffix) - 2]
+                    else:
+                        word = word[:-len(suffix)]
+
+                elif suffix == "keit":
+                    if "lich" in r2[-len(suffix) - 4:-len(suffix)]:
+                        word = word[:-len(suffix) - 4]
+
+                    elif "ig" in r2[-len(suffix) - 2:-len(suffix)]:
+                        word = word[:-len(suffix) - 2]
+                    else:
+                        word = word[:-len(suffix)]
+                break
+
+        # Umlaut accents are removed and
+        # 'u' and 'y' are put back into lower case.
+        word = (word.replace(u("\xE4"), "a").replace(u("\xF6"), "o")
+                    .replace(u("\xFC"), "u").replace("U", "u")
+                    .replace("Y", "y"))
+        return word