nltk language model (ngram) calculate the prob of a word from context

Question

I am using Python and NLTK to build a language model as follows:

from nltk.corpus import brown
from nltk.probability         


        

Answer 1

As regards your second question: this happens because "b" doesn't occur in the Brown corpus category news, as you can verify with:

>>> 'b' in brown.words(categories='news')
False

whereas

>>> 'word' in brown.words(categories='news')
True

I admit the error message is very cryptic, so you might want to file a bug report with the NLTK authors.