Chunking with nltk

Question

How can I obtain all the chunk from a sentence given a pattern. Exemple

NP:{<NN><NN>}

Sentence tagged:

[("money", "NN"), ("market", "NN") ("fund", "NN")]

If I parse I obtain

(S (NP money/NN market/NN) fund/NN)

I would like to have also the other alternative that is

(S money/NN (NP market/NN fund/NN))

Answer 1

I think your question is about getting the n most likely parses of a sentence. Am I right? If yes, see the nbest_parse(sent, n=None) function in the 2.0 documentation.

Answer 2

@mbatchkarov is right about the nbest_parse documentation. For the sake of code example see:

import nltk
# Define the cfg grammar.
grammar = nltk.parse_cfg("""
S -> NP
S -> NN NP
S -> NP NN
NP -> NN NN
NN -> 'market'
NN -> 'money'
NN -> 'fund'
""")

# Make your string into a list of tokens.
sentence = "money market fund".split(" ")

# Load the grammar into the ChartParser.
cp = nltk.ChartParser(grammar)

# Generate and print the nbest_parse from the grammar given the sentence tokens.
for tree in cp.nbest_parse(sentence):
    print tree