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Porter stemming algorithm in Python 3.
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| #!/usr/bin/env python3 | |
| """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 ([email protected]) | |
| Release 1: January 2001 | |
| Further adjustments by Santiago Bruno ([email protected]) | |
| to allow word input not restricted to one word per line, leading | |
| to: | |
| release 2: July 2008 | |
| -- | |
| Ported to Python 3 by Andrew Chan ([email protected]) | |
| """ | |
| 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, | |
| <c><v> gives 0 | |
| <c>vc<v> gives 1 | |
| <c>vcvc<v> gives 2 | |
| <c>vcvcvc<v> 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 <c>vcvc<v>.""" | |
| 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() |
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