我试图用 NLTK 检索搭配，但出现错误。我使用了内置的古腾堡语料库
我写：
alice = nltk.corpus.gutenberg.fileids()[7]
al = nltk.corpus.gutenberg.words(alice)
al_text = nltk.Text(al)
al_text.collocations(25)
我有：
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-16-a6905d575410> in <module>
----> 1 al_text.collocations(25)
C:\ProgramData\Anaconda3\lib\site-packages\nltk\text.py in collocations(self, num, window_size)
442
443 collocation_strings = [
--> 444 w1 + " " + w2 for w1, w2 in self.collocation_list(num, window_size)
445 ]
446 print(tokenwrap(collocation_strings, separator="; "))
C:\ProgramData\Anaconda3\lib\site-packages\nltk\text.py in <listcomp>(.0)
442
443 collocation_strings = [
--> 444 w1 + " " + w2 for w1, w2 in self.collocation_list(num, window_size) …