Estou treinando oNaiveBayesClassifier em Python usando frases, e isso me dá o erro abaixo. Eu não entendo qual pode ser o erro e qualquer ajuda seria boa.

Eu tentei muitos outros formatos de entrada, mas o erro permanece. O código fornecido abaixo:

from text.classifiers import NaiveBayesClassifier
from text.blob import TextBlob
train = [('I love this sandwich.', 'pos'),
         ('This is an amazing place!', 'pos'),
         ('I feel very good about these beers.', 'pos'),
         ('This is my best work.', 'pos'),
         ("What an awesome view", 'pos'),
         ('I do not like this restaurant', 'neg'),
         ('I am tired of this stuff.', 'neg'),
         ("I can't deal with this", 'neg'),
         ('He is my sworn enemy!', 'neg'),
         ('My boss is horrible.', 'neg') ]

test = [('The beer was good.', 'pos'),
        ('I do not enjoy my job', 'neg'),
        ("I ain't feeling dandy today.", 'neg'),
        ("I feel amazing!", 'pos'),
        ('Gary is a friend of mine.', 'pos'),
        ("I can't believe I'm doing this.", 'neg') ]
classifier = nltk.NaiveBayesClassifier.train(train)

Estou incluindo o rastreio abaixo.

Traceback (most recent call last):
  File "C:\Users\5460\Desktop\train01.py", line 15, in <module>
    all_words = set(word.lower() for passage in train for word in word_tokenize(passage[0]))
  File "C:\Users\5460\Desktop\train01.py", line 15, in <genexpr>
    all_words = set(word.lower() for passage in train for word in word_tokenize(passage[0]))
  File "C:\Python27\lib\site-packages\nltk\tokenize\__init__.py", line 87, in word_tokenize
    return _word_tokenize(text)
  File "C:\Python27\lib\site-packages\nltk\tokenize\treebank.py", line 67, in tokenize
    text = re.sub(r'^\"', r'``', text)
  File "C:\Python27\lib\re.py", line 151, in sub
    return _compile(pattern, flags).sub(repl, string, count)
TypeError: expected string or buffer