Python实现正向与逆向最大匹配分词算法详解

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发布时间：2026-10-13 | 6人浏览过

原创

本文介绍了在Python中实现正向最大匹配（FMM）和逆向最大匹配（BMM）分词的具体方法。通过定义词典加载、字符串切片及递归匹配逻辑，展示了两种算法在处理中文文本时的差异。代码包含完整的分词函数实现及主程序调用示例，适用于NLP基础场景下的分词需求分析。

正向最大匹配

# -*- coding:utf-8 -*-
 
CODEC='utf-8'
 
def u(s, encoding):
  'converted other encoding to unicode encoding'
  if isinstance(s, unicode):
    return s
  else:
    return unicode(s, encoding)
 
def fwd_mm_seg(wordDict, maxLen, str):
  'forward max match segment'
  wordList = []
  segStr = str
  segStrLen = len(segStr)
  for word in wordDict:
    print 'word: ', word
  print "\n"
  while segStrLen > 0:
    if segStrLen > maxLen:
      wordLen = maxLen
    else:
      wordLen = segStrLen
    subStr = segStr[0:wordLen]
    print "subStr: ", subStr
    while wordLen > 1:
      if subStr in wordDict:
        print "subStr1: %r" % subStr
        break
      else:
        print "subStr2: %r" % subStr
        wordLen = wordLen - 1
        subStr = subStr[0:wordLen]
#      print "subStr3: ", subStr
    wordList.append(subStr)
    segStr = segStr[wordLen:]
    segStrLen = segStrLen - wordLen
  for wordstr in wordList:
    print "wordstr: ", wordstr
  return wordList
    
      
def main():
  fp_dict = open('words.dic')
  wordDict = {}
  for eachWord in fp_dict:
    wordDict[u(eachWord.strip(), 'utf-8')] = 1
  segStr = u'你好世界hello world'
  print segStr
  wordList = fwd_mm_seg(wordDict, 10, segStr)
  print "==".join(wordList)
  
 
if __name__ == '__main__':
  main()

逆向最大匹配

# -*- coding:utf-8 -*-
 
 
def u(s, encoding):
  'converted other encoding to unicode encoding'
  if isinstance(s, unicode):
    return s
  else:
    return unicode(s, encoding)
 
CODEC='utf-8'
 
def bwd_mm_seg(wordDict, maxLen, str):
  'forward max match segment'
  wordList = []
  segStr = str
  segStrLen = len(segStr)
  for word in wordDict:
    print 'word: ', word
  print "\n"
  while segStrLen > 0:
    if segStrLen > maxLen:
      wordLen = maxLen
    else:
      wordLen = segStrLen
    subStr = segStr[-wordLen:None]
    print "subStr: ", subStr
    while wordLen > 1:
      if subStr in wordDict:
        print "subStr1: %r" % subStr
        break
      else:
        print "subStr2: %r" % subStr
        wordLen = wordLen - 1
        subStr = subStr[-wordLen:None]
#      print "subStr3: ", subStr
    wordList.append(subStr)
    segStr = segStr[0: -wordLen]
    segStrLen = segStrLen - wordLen
  wordList.reverse()
  for wordstr in wordList:
    print "wordstr: ", wordstr
  return wordList
    
      
def main():
  fp_dict = open('words.dic')
  wordDict = {}
  for eachWord in fp_dict:
    wordDict[u(eachWord.strip(), 'utf-8')] = 1
  segStr = ur'你好世界hello world'
  print segStr
  wordList = bwd_mm_seg(wordDict, 10, segStr)
  print "==".join(wordList)
 
if __name__ == '__main__':
  main()

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