# Natural Language Toolkit: RTE Classifier
#
# Copyright (C) 2001-2009 NLTK Project
# Author: Ewan Klein <ewan@inf.ed.ac.uk>
# URL: <http://www.nltk.org/>
# For license information, see LICENSE.TXT

"""
Simple classifier for RTE corpus.

It calculates the overlap in words and named entities between text and
hypothesis, and also whether there are words / named entities in the
hypothesis which fail to occur in the text, since this is an indicator that
the hypothesis is more informative than (i.e not entailed by) the text.

TO DO: better Named Entity classification
TO DO: add lemmatization
"""

import nltk
from util import accuracy

def ne(token):
    """
    This just assumes that words in all caps or titles are 
    named entities.
    
    @type token: C{str}
    """
    if token.istitle() or \
       token.isupper():
        return True
    return False

def lemmatize(word):
    """
    Use morphy from WordNet to find the base form of verbs.
    """
    lemma = nltk.corpus.wordnet.morphy(word, pos='verb')
    if lemma is not None:
        return lemma
    return word

class RTEFeatureExtractor(object):
    """
    This builds a bag of words for both the text and the hypothesis after
    throwing away some stopwords, then calculates overlap and difference.
    """
    def __init__(self, rtepair, stop=True, lemmatize=False):
        """
        @param rtepair: a L{RTEPair} from which features should be extracted
        @param stop: if C{True}, stopwords are thrown away.
        @type stop: C{bool}
        """
        self.stop = stop
        self.stopwords = set(['a', 'the', 'it', 'they', 'of', 'in', 'to',
                              'have', 'is', 'are', 'were', 'and', 'very', '.',','])
        
        self.negwords = set(['no', 'not', 'never', 'failed' 'rejected', 'denied'])
        # Try to tokenize so that abbreviations like U.S.and monetary amounts
        # like "$23.00" are kept as tokens.
        from nltk.tokenize import RegexpTokenizer
        tokenizer = RegexpTokenizer('([A-Z]\.)+|\w+|\$[\d\.]+')
        
        #Get the set of word types for text and hypothesis
        self.text_tokens = tokenizer.tokenize(rtepair.text)
        self.hyp_tokens = tokenizer.tokenize(rtepair.hyp)
        self.text_words = set(self.text_tokens)
        self.hyp_words = set(self.hyp_tokens)
        
        if lemmatize:
            self.text_words = set([lemmatize(token) for token in self.text_tokens])
            self.hyp_words = set([lemmatize(token) for token in self.hyp_tokens])
        
        if self.stop:
            self.text_words = self.text_words - self.stopwords
            self.hyp_words = self.hyp_words - self.stopwords
            
        self._overlap = self.hyp_words & self.text_words
        self._hyp_extra = self.hyp_words - self.text_words
        self._txt_extra = self.text_words - self.hyp_words
            
    
    def overlap(self, toktype, debug=False):
        """
        Compute the overlap between text and hypothesis.
        
        @param toktype: distinguish Named Entities from ordinary words
        @type toktype: 'ne' or 'word'
        """
        ne_overlap = set([token for token in self._overlap if ne(token)])
        if toktype == 'ne':
            if debug: print "ne overlap", ne_overlap
            return ne_overlap
        elif toktype == 'word':
            if debug: print "word overlap", self._overlap - ne_overlap
            return self._overlap - ne_overlap
        else:
            raise ValueError("Type not recognized:'%s'" % toktype)
    
    def hyp_extra(self, toktype, debug=True):
        """
        Compute the extraneous material in the hypothesis.
        
        @param toktype: distinguish Named Entities from ordinary words
        @type toktype: 'ne' or 'word'
        """
        ne_extra = set([token for token in self._hyp_extra if ne(token)])
        if toktype == 'ne':
            return ne_extra
        elif toktype == 'word':
            return self._hyp_extra - ne_extra
        else:
            raise ValueError("Type not recognized: '%s'" % toktype)
        
           
def rte_features(rtepair):
    extractor = RTEFeatureExtractor(rtepair)
    features = {}
    features['alwayson'] = True
    features['word_overlap'] = len(extractor.overlap('word'))
    features['word_hyp_extra'] = len(extractor.hyp_extra('word'))
    features['ne_overlap'] = len(extractor.overlap('ne'))
    features['ne_hyp_extra'] = len(extractor.hyp_extra('ne'))
    features['neg_txt'] = len(extractor.negwords & extractor.text_words)
    features['neg_hyp'] = len(extractor.negwords & extractor.hyp_words)
    return features            
           
    
def rte_classifier(trainer, features=rte_features):
    """
    Classify RTEPairs
    """
    train = [(pair, pair.value) for pair in nltk.corpus.rte.pairs(['rte1_dev.xml', 'rte2_dev.xml', 'rte3_dev.xml'])]
    test = [(pair, pair.value) for pair in nltk.corpus.rte.pairs(['rte1_test.xml', 'rte2_test.xml', 'rte3_test.xml'])]

    # Train up a classifier.
    print 'Training classifier...'
    classifier = trainer( [(features(pair), label) for (pair,label) in train] )

    # Run the classifier on the test data.
    print 'Testing classifier...'
    acc = accuracy(classifier, [(features(pair), label) for (pair,label) in test])
    print 'Accuracy: %6.4f' % acc

    # Return the classifier
    return classifier


def demo_features():
    pairs = nltk.corpus.rte.pairs(['rte1_dev.xml'])[:6]
    for pair in pairs:
        print
        for key in sorted(rte_features(pair)):
            print "%-15s => %s" % (key, rte_features(pair)[key])


def demo_feature_extractor():
    rtepair = nltk.corpus.rte.pairs(['rte3_dev.xml'])[33]
    extractor = RTEFeatureExtractor(rtepair)
    print extractor.hyp_words
    print extractor.overlap('word')
    print extractor.overlap('ne')	
    print extractor.hyp_extra('word')            
            

def demo():            
    import nltk
    try:
        nltk.config_megam('/usr/local/bin/megam')
        trainer = lambda x: nltk.MaxentClassifier.train(x, 'megam')
    except ValueError:
        try:
            trainer = lambda x: nltk.MaxentClassifier.train(x, 'BFGS')
        except ValueError:
            trainer = nltk.MaxentClassifier.train
    nltk.classify.rte_classifier(trainer)

if __name__ == '__main__':
    demo_features()
    demo_feature_extractor()           
    demo()
 
