excel如何查找默认文件扩展名

I'm trying to write and application that creates excel files using python and pywin32 and I'd like to save the file using the default format and extension for whatever version of excel the user is using. Depending on the version of excel they are using the default format could be "Open XML Workbook" which uses the ".xlsx" extension. Other times it could be the basic excel format and ".xls" extension. Plus the user can configure excel to use some other default format.I'm trying to write and application that create