原文：http://yongsun.me/2013/06/simple-implementation-of-mmseg-with-python/
Since I heard of MMSEG Chinese word segmentation algorithm (http://technology.chtsai.org/mmseg/) many years ago, I finally implemented it with Python as a programing practice in my team, dictionary file and character frequencies from mmseg4j project.
#!/usr/bin/python
# -*- encoding: UTF-8 -*-
import codecs
import sys
from math import log
from collections import defaultdict
class Trie (object):
class TrieNode:
def __init__ (self):
self.val = 0
self.trans = {}
def __init__ (self):
self.root = Trie.TrieNode()
def __walk (self, trienode, ch):
if ch in trienode.trans:
trienode = trienode.trans[ch]
return trienode, trienode.val
else:
return None, 0
def add (self, word, value=1):
curr_node = self.root
for ch in word:
try:
curr_node = curr_node.trans[ch]
except:
curr_node.trans[ch] = Trie.TrieNode()
curr_node = curr_node.trans[ch]
curr_node.val = value
def match_all (self, word):
ret = []
curr_node = self.root
for ch in word:
curr_node, val = self.__walk (curr_node, ch)
if not curr_node:
break
if val:
ret.append (val)
return ret
class Dict (Trie):
def __init__(self, fname):
super (Dict, self).__init__()
self.load(fname)
def load(self, fname):
file = codecs.open(fname, 'r', 'utf-8')
for line in file:
word = line.strip()
self.add(word, word)
file.close()
class CharFreqs (defaultdict):
def __init__ (self, fname):
super (CharFreqs, self).__init__(lambda:1)
self.load(fname)
def load (self, fname):
file = codecs.open(fname, 'r', 'utf-8')
for line in file:
ch, freq = line.strip().split()
self[ch] = freq
file.close()
class MMSeg:
class Chunk:
def __init__ (self, words, chrs):
self.words = words
self.lens = map(lambda x:len(x), words)
self.length = sum(self.lens)
self.mean = float(self.length) / len(words)
self.var = sum(map(lambda x: (x-self.mean)**2, self.lens)) / len(self.words)
self.degree = sum([log(float(chrs[x])) for x in words if len(x)==1])
def __str__ (self):
return ' '.join(self.words).encode('UTF-8') + \
"(%f %f %f %f)" % (self.length, self.mean, self.var, self.degree)
def __lt__ (self, other):
return (self.length, self.mean, -self.var, self.degree) < \
(other.length, other.mean, -other.var, other.degree)
def __init__(self, dic, chrs):
self.dic = dic
self.chrs = chrs
def __get_chunks (self, s, depth=3):
ret = []
def __get_chunks_it (s, num, segs):
if (num == 0 or not s) and segs:
ret.append(MMSeg.Chunk(segs, self.chrs))
else:
m = self.dic.match_all(s)
if not m:
__get_chunks_it (s[1:], num-1, segs+[s[0]])
for w in m:
__get_chunks_it (s[len(w):], num-1, segs+[w])
__get_chunks_it (s, depth, [])
return ret
def segment (self, s):
while s:
chunks = self.__get_chunks(s)
best = max(chunks)
yield best.words[0]
s = s[len(best.words[0]):]
if __name__ == "__main__":
dic = Dict("dict.utf8")
chrs = CharFreqs("chars.utf8")
mmseg = MMSeg(dic, chrs)
enc = sys.getfilesystemencoding()
while True:
try:
s = raw_input ("Test String: ")
except:
break
print "Test Result: ",
for w in mmseg.segment(s.decode(enc)):
print w.encode(enc),
print '\n'
# -*- indent-tabs-mode: nil -*- vim:et:ts=4