How to use the sacremoses.util.grouper function in sacremoses

def _load_model(self, filename):
        """
        Loads pre-trained truecasing file.

        :returns: A dictionary of the best, known objects as values from `_casing_to_model()`
        :rtype: {'best': dict, 'known': Counter}
        """
        casing = defaultdict(Counter)
        with open(filename, encoding=self.encoding) as fin:
            for line in fin:
                line = line.strip().split()
                for token, count in grouper(line, 2):
                    count = count.split("/")[0].strip("()")
                    casing[token.lower()][token] = int(count)
        # Returns the best and known object from `_casing_to_model()`
        return self._casing_to_model(casing)