NLTK wordnet界面中的第0个synset

Question

From the semcor corpus ( http://www.cse.unt.edu/~rada/downloads.html ), there are senses wasn't mapped to the later versions of wordnet. And magically, the mapping can be found in the NLTK WordNet API as such:

>>> from nltk.corpus import wordnet as wn
# Emunerate the possible senses for the lemma 'delayed'
>>> wn.synsets('delayed')
[Synset('delay.v.01'), Synset('delay.v.02'), Synset('stay.v.06'), Synset('check.v.07'), Synset('delayed.s.01')]
>>> wn.synset('delay.v.01')
Synset('delay.v.01')
# Magically, there is a 0th sense of the word!!!
>>> wn.synset('delayed.a.0')
Synset('delayed.s.01')

I've checked the code and the API ( http://nltk.googlecode.com/svn/trunk/doc/api/nltk.corpus.reader.wordnet.Synset-class.html , http://nltk.org/_modules/nltk/corpus/reader/wordnet.html ) but i can't find how they did the magically mapping that didn't shouldn't exist (eg for delayed.a.0 -> delayed.s.01 ).

Does anyone know which part of the NLTK Wordnet API code does the magical mapping?

Answer 1

It's a bug I guess. When you do wn.synset('delayed.a.0') the first two lines in the method are:

lemma, pos, synset_index_str = name.lower().rsplit('.', 2)
synset_index = int(synset_index_str) - 1

So in this case the value of synset_index is -1 which is a valid index in python. And it won't fail when looking up in the array of synsets whose lemma is delayed and pos is a .

With this behavior you can do tricky things like:

>>> wn.synset('delay.v.-1')
Synset('stay.v.06')