How to use the nbsite.gallery.thumbnailer.ThumbnailProcessor function in nbsite

def notebook_thumbnail(filename, subpath):
    basename = os.path.splitext(os.path.basename(filename))[0]
    dir_path = os.path.abspath(os.path.join(subpath, 'thumbnails'))
    absdirpath= os.path.abspath(os.path.join('.', dir_path))
    if not os.path.exists(absdirpath):
        os.makedirs(absdirpath)

    preprocessors = [OptsMagicProcessor(),
                     OutputMagicProcessor(),
                     StripTimeMagicsProcessor(),
                     StripServableSemicolonsProcessor(),
                     StripMagicsProcessor(),
                     ThumbnailProcessor(os.path.abspath(os.path.join(dir_path, basename)))]
    return export_to_python(filename, preprocessors)

def __init__(self, basename, **kwargs):
        self.basename = basename
        super(ThumbnailProcessor, self).__init__(**kwargs)