NLTK:如何遍历名词短语以返回字符串列表?


问题内容

在NLTK中,如何遍历解析的句子以返回名词短语字符串列表?

我有两个目标:
(1)创建名词短语列表,而不是使用“
traverse()”方法将其打印出来。我目前使用StringIO记录现有traverse()方法的输出。那不是可接受的解决方案。
(2)取消解析名词短语字符串,以便:“(NP Michael / NNP Jackson / NNP)”成为“ Michael
Jackson”。NLTK中是否有一种可以解析的方法?

NLTK文档建议使用traverse()查看名词短语,但是如何在此递归方法中捕获“ t”,以便生成字符串名词短语列表?

from nltk.tag import pos_tag

def traverse(t):
  try:
      t.label()
  except AttributeError:
      return
  else:
      if t.label() == 'NP': print(t)  # or do something else
      else:
          for child in t: 
              traverse(child)

def nounPhrase(tagged_sent):
    # Tag sentence for part of speech
    tagged_sent = pos_tag(sentence.split())  # List of tuples with [(Word, PartOfSpeech)]
    # Define several tag patterns
    grammar = r"""
      NP: {<DT|PP\$>?<JJ>*<NN>}   # chunk determiner/possessive, adjectives and noun
      {<NNP>+}                # chunk sequences of proper nouns
      {<NN>+}                 # chunk consecutive nouns
      """
    cp = nltk.RegexpParser(grammar)  # Define Parser
    SentenceTree = cp.parse(tagged_sent)
    NounPhrases = traverse(SentenceTree)   # collect Noun Phrase
    return(NounPhrases)

sentence = "Michael Jackson likes to eat at McDonalds"
tagged_sent = pos_tag(sentence.split())  
NP = nounPhrase(tagged_sent)  
print(NP)

当前打印:
(NP Michael / NNP Jackson / NNP)
(NP McDonalds / NNP)
并将“ None”存储到NP


问题答案:
def extract_np(psent):
  for subtree in psent.subtrees():
    if subtree.label() == 'NP':
      yield ' '.join(word for word, tag in subtree.leaves())


cp = nltk.RegexpParser(grammar)
parsed_sent = cp.parse(tagged_sent)
for npstr in extract_np(parsed_sent):
    print (npstr)