@classmethod
    def from_words(cls, words, window_size=2):
        """Construct a BigramCollocationFinder for all bigrams in the given
        sequence.  When window_size > 2, count non-contiguous bigrams, in the
        style of Church and Hanks's (1990) association ratio.
        """
        wfd = FreqDist()
        bfd = FreqDist()

        if 2 < window_size:
            raise ValueError("Specify window_size at least 2")

        for window in ngrams(words, window_size, pad_right=True):
            w1 = window[0]
            if w1 is None:
                continue
            wfd[w1] += 1
            for w2 in window[1:]:
                if w2 is not None:
                    bfd[(w1, w2)] += 1
        return cls(wfd, bfd, window_size=window_size)
dataset/ETHPy150Open nltk/nltk/nltk/collocations.py/BigramCollocationFinder.from_words/swapped operands of `<`