python–NLTK停用词删除问题

我正在尝试做一个document classification,as described in NLTK Chapter 6,而我在删除停用词时遇到了麻烦.当我添加

all_words = (w for w in all_words if w not in nltk.corpus.stopwords.words('english'))

它返回

Traceback (most recent call last):  file "fiction.py",line 8,in 

我猜测停用词代码改变了用于’all_words’的对象类型,使得它们.key()函数无用.如何在使用键功能之前删除停用词而不更改其类型？完整代码如下：

import nltk from nltk.corpus import PlaintextCorpusReadercorpus_root = './nltk_data/corpora/fiction'fiction = PlaintextCorpusReader(corpus_root,'.*')all_words=nltk.Freqdist(w.lower() for w in fiction.words())all_words = (w for w in all_words if w not in nltk.corpus.stopwords.words('english'))word_features = all_words.keys()[:100]def document_features(document): # [_document-classify-extractor]    document_words = set(document) # [_document-classify-set]    features = {}    for word in word_features:        features['contains(%s)' % word] = (word in document_words)    return featuresprint document_features(fiction.words('fic/11.txt'))

all_words=nltk.Freqdist(w.lower() for w in fiction.words() if w.lower() not in nltk.corpus.stopwords.words('english'))

stopword_set = froZenset(ntlk.corpus.stopwords.words('english'))

for stopword in nltk.corpus.stopwords.words('english'):    if stopword in all_words:        del all_words[stopword]