How to use the pywb.utils.loaders.to_native_str function in pywb

def __call__(self, filename, cdx=None):
        with open(self.pathindex_file, 'rb') as reader:
            result = iter_exact(reader, filename.encode('utf-8'), b'\t')

            for pathline in result:
                paths = pathline.split(b'\t')[1:]
                for path in paths:
                    yield to_native_str(path, 'utf-8')

err_url = None

        if len(exc.args):
            err_msg = str(exc.args[0])

        if print_trace:
            import traceback
            err_details = traceback.format_exc()
            print(err_details)
        else:
            logging.info(err_msg)
            err_details = None

        if error_view:
            if err_url and isinstance(err_url, str):
                err_url = to_native_str(err_url, 'utf-8')
            if err_msg and isinstance(err_msg, str):
                err_msg = to_native_str(err_msg, 'utf-8')

            return error_view.render_response(exc_type=type(exc).__name__,
                                              err_msg=err_msg,
                                              err_details=err_details,
                                              status=status,
                                              env=env,
                                              err_url=err_url)
        else:
            msg = status + ' Error: '
            if err_msg:
                msg += err_msg

            #msg = msg.encode('utf-8', 'ignore')
            return WbResponse.text_response(msg,

def readline():
            return to_native_str(stream.readline())

if len(exc.args):
            err_msg = str(exc.args[0])

        if print_trace:
            import traceback
            err_details = traceback.format_exc()
            print(err_details)
        else:
            logging.info(err_msg)
            err_details = None

        if error_view:
            if err_url and isinstance(err_url, str):
                err_url = to_native_str(err_url, 'utf-8')
            if err_msg and isinstance(err_msg, str):
                err_msg = to_native_str(err_msg, 'utf-8')

            return error_view.render_response(exc_type=type(exc).__name__,
                                              err_msg=err_msg,
                                              err_details=err_details,
                                              status=status,
                                              env=env,
                                              err_url=err_url)
        else:
            msg = status + ' Error: '
            if err_msg:
                msg += err_msg

            #msg = msg.encode('utf-8', 'ignore')
            return WbResponse.text_response(msg,
                                            status=status)

def __call__(self, filename, cdx=None):
        redis_val = self.redis.hget(self.key_prefix + filename, 'path')
        return [to_native_str(redis_val, 'utf-8')] if redis_val else []