def _post_save_script(model, os_path, contents_manager, **kwargs):
    """convert notebooks to Python script after save with nbconvert
    replaces `jupyter notebook --script`
    """
    from nbconvert.exporters.script import ScriptExporter
    warnings.warn("`_post_save_script` is deprecated and will be removed in Notebook 5.0", DeprecationWarning)

    if model['type'] != 'notebook':
        return

    global _script_exporter
    if _script_exporter is None:
        _script_exporter = ScriptExporter(parent=contents_manager)
    log = contents_manager.log

    base, ext = os.path.splitext(os_path)
    script, resources = _script_exporter.from_filename(os_path)
    script_fname = base + resources.get('output_extension', '.txt')
    log.info("Saving script /%s", to_api_path(script_fname, contents_manager.root_dir))
    with io.open(script_fname, 'w', encoding='utf-8') as f:
        f.write(script)