Why does zipfile.is_zipfile returns True on xlsx file?

Question

I am using is_zipfile 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 is_zipfiile? Thanks.

Answer 1

Quoting from the Microsoft's XLSX Structure overview doc,

Workbook data is contained in a ZIP package conforming to the Open Packaging Conventions

So, .xlsx files are actually zip files only. If you want not to consider them as a zip file, you may have to exclude with an if condition like this

if os.path.splitext(filename)[1] != ".xlsx" and zipfile.is_file(filename):