title: Why does zipfile.is_zipfile returns True on xlsx file?
body: <p>I am using <code>is_zipfile</code> to check if it is a zipfile before extracting it. But the method returns True on excel file from a StringIO object. I am using Python 2.7. Does anyone know how to fix this? Is it reliable to use <code>is_zipfiile</code>? Thanks.</p>