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# Natural Language Toolkit: API for Language Models 

# 

# Copyright (C) 2001-2012 NLTK Project 

# Author: Steven Bird <sb@csse.unimelb.edu.au> 

# URL: <http://www.nltk.org/> 

# For license information, see LICENSE.TXT 

 

 

# should this be a subclass of ConditionalProbDistI? 

 

class ModelI(object): 

    """ 

    A processing interface for assigning a probability to the next word. 

    """ 

 

    def __init__(self): 

        '''Create a new language model.''' 

        raise NotImplementedError() 

 

    def prob(self, word, context): 

        '''Evaluate the probability of this word in this context.''' 

        raise NotImplementedError() 

 

    def logprob(self, word, context): 

        '''Evaluate the (negative) log probability of this word in this context.''' 

        raise NotImplementedError() 

 

    def choose_random_word(self, context): 

        '''Randomly select a word that is likely to appear in this context.''' 

        raise NotImplementedError() 

 

    def generate(self, n): 

        '''Generate n words of text from the language model.''' 

        raise NotImplementedError() 

 

    def entropy(self, text): 

        '''Evaluate the total entropy of a message with respect to the model. 

        This is the sum of the log probability of each word in the message.''' 

        raise NotImplementedError()