Debugging 在python中调试maxmatch算法时遇到问题

与nltk中的单词列表相比，我一直在研究一种maxmatch算法来标记hashtags，但我在调试方面遇到了麻烦

算法要点如下：

function MAXMATCH (sentence, dictionary D) returns word sequence W
  if sentence is empty
    return empty list
  for i ← length(sentence) downto 1
    firstword = first i chars of sentence
    remainder = rest of sentence
    if InDictionary(firstword, D)
      return list(firstword, MaxMatch(remainder,dictionary) )
# no word was found, so make a one-character word
  firstword = first char of sentence
  remainder = rest of sentence
  return list(firstword, MaxMatch(remainder,dictionary) )

下面是我的python实现。 我在这里和那里插入了一些试图调试的

print

from nltk.corpus import words # words is a Python list
wordlist = set(words.words())

lst = []
def max_match(hashtag, wordlist):
    if not hashtag:
        return None
    for i in range(len(hashtag)-1, -1, -1):
        first_word = (hashtag[0:i+1])
        print "Firstword: " + first_word
        remainder = hashtag[i+1:len(hashtag)]
        print "Remainder: " + remainder
        if first_word in wordlist:
            print "Found: " + first_word
            lst.append(first_word)
            print lst
            max_match(remainder, wordlist)

# if no word is found, make one-character word
    first_word = hashtag[0]
    remainder = hashtag[1:len(hashtag)]
    lst.append(first_word)
    max_match(remainder, wordlist)
    return lst

print max_match('labourvictory', wordlist)

最后一行，

print max_match（'labourvictory'，wordlist）

应该返回list['labour'，victory'，我希望它退出，因为

如果不是hashtag，则返回None

部分，然而，由于我不明白它为什么会继续运行，一切都会失控

---

在递归函数中，最常见的错误是没有在正确的点返回值。我根据给定的伪代码要点修改了您的代码。代码中的问题是，当您在字典中找到一个单词时，您没有返回任何值

def max_match(hashtag, wordlist):
    if not hashtag:
        return []
    for i in range(len(hashtag)-1, -1, -1):
        first_word = (hashtag[0:i+1])
        remainder = hashtag[i+1:len(hashtag)]
        if first_word in wordlist:
            return [first_word] + max_match(remainder, wordlist)

    # if no word is found, make one-character word
    first_word = hashtag[0]
    remainder = hashtag[1:len(hashtag)]

    return [first_word] + max_match(remainder, wordlist)