python - POS tagging - NLTK thinks noun is adjective

Question

In the following code, why does nltk think 'fish' is an adjective and not a noun?

>>> import nltk
>>> s = "a woman needs a man like a fish needs a bicycle"
>>> nltk.pos_tag(s.split())
[('a', 'DT'), ('woman', 'NN'), ('needs', 'VBZ'), ('a', 'DT'), ('man', 'NN'), ('like', 'IN'), ('a', 'DT'), ('fish', 'JJ'), ('needs', 'NNS'), ('a', 'DT'), ('bicycle', 'NN')]

Answer 1

I am not sure what is the workaround but you can check the source here https://nltk.googlecode.com/svn/trunk/nltk/nltk/tag/

Meanwhile I tried your sentence with little different approach.

>>> s = "a woman needs a man. A fish needs a bicycle"
>>> nltk.pos_tag(s.split())
[('a', 'DT'), ('woman', 'NN'), ('needs', 'VBZ'), ('a', 'DT'), ('man.', NP'), ('A','NNP'),   ('fish', 'NN'), ('needs', 'VBZ'), ('a', 'DT'), ('bicycle', 'NN')]

which resulted in fish as "NN".