def __init__(self, fname, index_fname=None):
        """
        Initialize this abstract base class, by loading a previously saved index
        from `index_fname` (or `fname.index` if `index_fname` is not set).
        This index will allow subclasses to support the `corpus[docno]` syntax
        (random access to document #`docno` in O(1)).

        >>> # save corpus in SvmLightCorpus format with an index
        >>> corpus = [[(1, 0.5)], [(0, 1.0), (1, 2.0)]]
        >>> gensim.corpora.SvmLightCorpus.serialize('testfile.svmlight', corpus)
        >>> # load back as a document stream (*not* plain Python list)
        >>> corpus_with_random_access = gensim.corpora.SvmLightCorpus('tstfile.svmlight')
        >>> print(corpus_with_random_access[1])
        [(0, 1.0), (1, 2.0)]

        """
        try:
            if index_fname is None:
                index_fname = fname + '.index'
            self.index = utils.unpickle(index_fname)
            logger.info(index_fname % "loaded corpus index from %s")
        except:
            self.index = None
        self.length = None
dataset/ETHPy150Open largelymfs/topical_word_embeddings/TWE-1/gensim/corpora/indexedcorpus.py/IndexedCorpus.__init__/swapped operands of `%`