#!/usr/bin/env python """Porter Stemming Algorithm This is the Porter stemming algorithm, ported to Python from the version coded up in ANSI C by the author. It may be be regarded as canonical, in that it follows the algorithm presented in Porter, 1980, An algorithm for suffix stripping, Program, Vol. 14, no. 3, pp 130-137, only differing from it at the points maked --DEPARTURE-- below. See also http://www.tartarus.org/~martin/PorterStemmer The algorithm as described in the paper could be exactly replicated by adjusting the points of DEPARTURE, but this is barely necessary, because (a) the points of DEPARTURE are definitely improvements, and (b) no encoding of the Porter stemmer I have seen is anything like as exact as this version, even with the points of DEPARTURE! Vivake Gupta (v@nano.com) Release 1: January 2001 Further adjustments by Santiago Bruno (bananabruno@gmail.com) to allow word input not restricted to one word per line, leading to: release 2: July 2008 """ import sys class PorterStemmer: def __init__(self): """The main part of the stemming algorithm starts here. b is a buffer holding a word to be stemmed. The letters are in b[k0], b[k0+1] ... ending at b[k]. In fact k0 = 0 in this demo program. k is readjusted downwards as the stemming progresses. Zero termination is not in fact used in the algorithm. Note that only lower case sequences are stemmed. Forcing to lower case should be done before stem(...) is called. """ self.b = "" # buffer for word to be stemmed self.k = 0 self.k0 = 0 self.j = 0 # j is a general offset into the string def cons(self, i): """cons(i) is TRUE <=> b[i] is a consonant.""" if self.b[i] == 'a' or self.b[i] == 'e' or self.b[i] == 'i' or self.b[i] == 'o' or self.b[i] == 'u': return 0 if self.b[i] == 'y': if i == self.k0: return 1 else: return (not self.cons(i - 1)) return 1 def m(self): """m() measures the number of consonant sequences between k0 and j. if c is a consonant sequence and v a vowel sequence, and <..> indicates arbitrary presence, gives 0 vc gives 1 vcvc gives 2 vcvcvc gives 3 .... """ n = 0 i = self.k0 while 1: if i > self.j: return n if not self.cons(i): break i = i + 1 i = i + 1 while 1: while 1: if i > self.j: return n if self.cons(i): break i = i + 1 i = i + 1 n = n + 1 while 1: if i > self.j: return n if not self.cons(i): break i = i + 1 i = i + 1 def vowelinstem(self): """vowelinstem() is TRUE <=> k0,...j contains a vowel""" for i in range(self.k0, self.j + 1): if not self.cons(i): return 1 return 0 def doublec(self, j): """doublec(j) is TRUE <=> j,(j-1) contain a double consonant.""" if j < (self.k0 + 1): return 0 if (self.b[j] != self.b[j-1]): return 0 return self.cons(j) def cvc(self, i): """cvc(i) is TRUE <=> i-2,i-1,i has the form consonant - vowel - consonant and also if the second c is not w,x or y. this is used when trying to restore an e at the end of a short e.g. cav(e), lov(e), hop(e), crim(e), but snow, box, tray. """ if i < (self.k0 + 2) or not self.cons(i) or self.cons(i-1) or not self.cons(i-2): return 0 ch = self.b[i] if ch == 'w' or ch == 'x' or ch == 'y': return 0 return 1 def ends(self, s): """ends(s) is TRUE <=> k0,...k ends with the string s.""" length = len(s) if s[length - 1] != self.b[self.k]: # tiny speed-up return 0 if length > (self.k - self.k0 + 1): return 0 if self.b[self.k-length+1:self.k+1] != s: return 0 self.j = self.k - length return 1 def setto(self, s): """setto(s) sets (j+1),...k to the characters in the string s, readjusting k.""" length = len(s) self.b = self.b[:self.j+1] + s + self.b[self.j+length+1:] self.k = self.j + length def r(self, s): """r(s) is used further down.""" if self.m() > 0: self.setto(s) def step1ab(self): """step1ab() gets rid of plurals and -ed or -ing. e.g. caresses -> caress ponies -> poni ties -> ti caress -> caress cats -> cat feed -> feed agreed -> agree disabled -> disable matting -> mat mating -> mate meeting -> meet milling -> mill messing -> mess meetings -> meet """ if self.b[self.k] == 's': if self.ends("sses"): self.k = self.k - 2 elif self.ends("ies"): self.setto("i") elif self.b[self.k - 1] != 's': self.k = self.k - 1 if self.ends("eed"): if self.m() > 0: self.k = self.k - 1 elif (self.ends("ed") or self.ends("ing")) and self.vowelinstem(): self.k = self.j if self.ends("at"): self.setto("ate") elif self.ends("bl"): self.setto("ble") elif self.ends("iz"): self.setto("ize") elif self.doublec(self.k): self.k = self.k - 1 ch = self.b[self.k] if ch == 'l' or ch == 's' or ch == 'z': self.k = self.k + 1 elif (self.m() == 1 and self.cvc(self.k)): self.setto("e") def step1c(self): """step1c() turns terminal y to i when there is another vowel in the stem.""" if (self.ends("y") and self.vowelinstem()): self.b = self.b[:self.k] + 'i' + self.b[self.k+1:] def step2(self): """step2() maps double suffices to single ones. so -ization ( = -ize plus -ation) maps to -ize etc. note that the string before the suffix must give m() > 0. """ if self.b[self.k - 1] == 'a': if self.ends("ational"): self.r("ate") elif self.ends("tional"): self.r("tion") elif self.b[self.k - 1] == 'c': if self.ends("enci"): self.r("ence") elif self.ends("anci"): self.r("ance") elif self.b[self.k - 1] == 'e': if self.ends("izer"): self.r("ize") elif self.b[self.k - 1] == 'l': if self.ends("bli"): self.r("ble") # --DEPARTURE-- # To match the published algorithm, replace this phrase with # if self.ends("abli"): self.r("able") elif self.ends("alli"): self.r("al") elif self.ends("entli"): self.r("ent") elif self.ends("eli"): self.r("e") elif self.ends("ousli"): self.r("ous") elif self.b[self.k - 1] == 'o': if self.ends("ization"): self.r("ize") elif self.ends("ation"): self.r("ate") elif self.ends("ator"): self.r("ate") elif self.b[self.k - 1] == 's': if self.ends("alism"): self.r("al") elif self.ends("iveness"): self.r("ive") elif self.ends("fulness"): self.r("ful") elif self.ends("ousness"): self.r("ous") elif self.b[self.k - 1] == 't': if self.ends("aliti"): self.r("al") elif self.ends("iviti"): self.r("ive") elif self.ends("biliti"): self.r("ble") elif self.b[self.k - 1] == 'g': # --DEPARTURE-- if self.ends("logi"): self.r("log") # To match the published algorithm, delete this phrase def step3(self): """step3() dels with -ic-, -full, -ness etc. similar strategy to step2.""" if self.b[self.k] == 'e': if self.ends("icate"): self.r("ic") elif self.ends("ative"): self.r("") elif self.ends("alize"): self.r("al") elif self.b[self.k] == 'i': if self.ends("iciti"): self.r("ic") elif self.b[self.k] == 'l': if self.ends("ical"): self.r("ic") elif self.ends("ful"): self.r("") elif self.b[self.k] == 's': if self.ends("ness"): self.r("") def step4(self): """step4() takes off -ant, -ence etc., in context vcvc.""" if self.b[self.k - 1] == 'a': if self.ends("al"): pass else: return elif self.b[self.k - 1] == 'c': if self.ends("ance"): pass elif self.ends("ence"): pass else: return elif self.b[self.k - 1] == 'e': if self.ends("er"): pass else: return elif self.b[self.k - 1] == 'i': if self.ends("ic"): pass else: return elif self.b[self.k - 1] == 'l': if self.ends("able"): pass elif self.ends("ible"): pass else: return elif self.b[self.k - 1] == 'n': if self.ends("ant"): pass elif self.ends("ement"): pass elif self.ends("ment"): pass elif self.ends("ent"): pass else: return elif self.b[self.k - 1] == 'o': if self.ends("ion") and (self.b[self.j] == 's' or self.b[self.j] == 't'): pass elif self.ends("ou"): pass # takes care of -ous else: return elif self.b[self.k - 1] == 's': if self.ends("ism"): pass else: return elif self.b[self.k - 1] == 't': if self.ends("ate"): pass elif self.ends("iti"): pass else: return elif self.b[self.k - 1] == 'u': if self.ends("ous"): pass else: return elif self.b[self.k - 1] == 'v': if self.ends("ive"): pass else: return elif self.b[self.k - 1] == 'z': if self.ends("ize"): pass else: return else: return if self.m() > 1: self.k = self.j def step5(self): """step5() removes a final -e if m() > 1, and changes -ll to -l if m() > 1. """ self.j = self.k if self.b[self.k] == 'e': a = self.m() if a > 1 or (a == 1 and not self.cvc(self.k-1)): self.k = self.k - 1 if self.b[self.k] == 'l' and self.doublec(self.k) and self.m() > 1: self.k = self.k -1 def stem(self, p, i, j): """In stem(p,i,j), p is a char pointer, and the string to be stemmed is from p[i] to p[j] inclusive. Typically i is zero and j is the offset to the last character of a string, (p[j+1] == '\0'). The stemmer adjusts the characters p[i] ... p[j] and returns the new end-point of the string, k. Stemming never increases word length, so i <= k <= j. To turn the stemmer into a module, declare 'stem' as extern, and delete the remainder of this file. """ # copy the parameters into statics self.b = p self.k = j self.k0 = i if self.k <= self.k0 + 1: return self.b # --DEPARTURE-- # With this line, strings of length 1 or 2 don't go through the # stemming process, although no mention is made of this in the # published algorithm. Remove the line to match the published # algorithm. self.step1ab() self.step1c() self.step2() self.step3() self.step4() self.step5() return self.b[self.k0:self.k+1] if __name__ == '__main__': p = PorterStemmer() if len(sys.argv) > 1: for f in sys.argv[1:]: infile = open(f, 'r') while 1: output = '' word = '' line = infile.readline() if line == '': break for c in line: if c.isalpha(): word += c.lower() else: if word: output += p.stem(word, 0,len(word)-1) word = '' output += c.lower() print output, infile.close()