def score_ngram(self, score_fn, w1, w2):
        """Returns the score for a given bigram using the given scoring
        function.  Following Church and Hanks (1990), counts are scaled by
        a factor of 1/(window_size - 1).
        """
        n_all = self.N
        n_ii = self.ngram_fd[(w1, w2)] / (self.window_size - 1.0)
        if not n_ii:
            return
        n_ix = self.word_fd[w1]
        n_xi = self.word_fd[w2]
        return score_fn(n_ii, (n_ix, n_xi), n_all)
dataset/ETHPy150Open nltk/nltk/nltk/collocations.py/BigramCollocationFinder.score_ngram/original