Python容错的前缀树实现中文纠错
实现
参考
介绍
本文使用 Python 实现了前缀树，并且支持编辑距离容错的查询。文中的前缀树只存储了三个分词，格式为 (分词字符串,频率) ，如：(’中海晋西园’, 2)、(’中海西园’, 24)、(’中南海’, 4)，可以换成自己的文件进行数据的替换。在查询的时候要指定一个字符串和最大的容错编辑距离。
实现
class Word: def __init__(self, word, freq): self.word = word self.freq = freqclass Trie: def __init__(self): self.root = LetterNode(’’) self.START = 3 def insert(self, word, freq): self.root.insert(word, freq, 0) def findAll(self, query, maxDistance): suggestions = self.root.recommend(query, maxDistance, self.START) return sorted(set(suggestions), key=lambda x: x.freq)class LetterNode: def __init__(self, char): self.REMOVE = -1 self.ADD = 1 self.SAME = 0 self.CHANGE = 2 self.START = 3 self.pointers = [] self.char = char self.word = None def charIs(self, c): return self.char == c def insert(self, word, freq, depth): if ’ ’ in word: word = [i for i in word.split(’ ’)] if depth < len(word): c = word[depth].lower() for next in self.pointers: if next.charIs(c): return next.insert(word, freq, depth + 1) nextNode = LetterNode(c) self.pointers.append(nextNode) return nextNode.insert(word, freq, depth + 1) else: self.word = Word(word, freq) def recommend(self, query, movesLeft, lastAction): suggestions = [] length = len(query) if length >= 0 and movesLeft - length >= 0 and self.word: suggestions.append(self.word) if movesLeft == 0 and length > 0: for next in self.pointers: if next.charIs(query[0]): suggestions += next.recommend(query[1:], movesLeft, self.SAME) break elif movesLeft > 0: for next in self.pointers: if length > 0: if next.charIs(query[0]): suggestions += next.recommend(query[1:], movesLeft, self.SAME) else: suggestions += next.recommend(query[1:], movesLeft - 1, self.CHANGE) if lastAction != self.CHANGE and lastAction != self.REMOVE: suggestions += next.recommend(query, movesLeft - 1, self.ADD) if lastAction != self.ADD and lastAction != self.CHANGE: if length > 1 and next.charIs(query[1]): suggestions += next.recommend(query[2:], movesLeft - 1, self.REMOVE) elif length > 2 and next.charIs(query[2]) and movesLeft == 2: suggestions += next.recommend(query[3:], movesLeft - 2, self.REMOVE) else: if lastAction != self.CHANGE and lastAction != self.REMOVE: suggestions += next.recommend(query, movesLeft - 1, self.ADD) return suggestionsdef buildTrieFromFile(): trie = Trie() rows = [(’中海晋西园’, 2),(’中海西园’, 24),(’中南海’, 4)] for row in rows: trie.insert(row[0], int(row[1])) return triedef suggestor(trie, s, maxDistance): if ’ ’ in s: s = [x for x in s.split(’ ’)] suggestions = trie.findAll(s, maxDistance) return [str(x.word) for x in suggestions]if __name__ == "__main__": trie = buildTrieFromFile() r = suggestor(trie, ’中海晋西园’, 1) print(r)
分析
结果打印：
[’中海晋西园’, ’中海西园’]
可以看出“中海晋西园”是和输入完全相同的字符串，编辑距离为 0 ，所以符合最大编辑距离为 1 的要求，直接返回。
“中海西园”是“中海晋西园”去掉“晋”字之后的结果，编辑距离为 1， 所以符合最大编辑距离为 1 的要求，直接返回。
另外，“中南海”和“中海晋西园”的编辑距离为 4 ，不符合最大编辑距离为 1 的要求，所以结果中没有出现。
参考
https://github.com/leoRoss/AutoCorrectTrie
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