text: #!/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,
  
             <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]