Object "inc" with NLTK for py 2.7

I just downloaded nltk this morning and already faced the problem of repeating my code.

I get

AttributeError: 'FreqDist' object has no attribute 'inc'

      

        
        
        
      

    

I had the same error with this code,

for word in gutenberg.words(’austen-persuasion.txt’):
    fd.inc(word)

      

        
        
        
      

    

but just changed it to

fd[word] += 1

      

        
        
        
      

    

However, where can I go when I come across the code below?

for word in gutenberg.words(u'austen-persuasion.txt'):
    cfd[prev_word].inc(word)
    prev_word = word