Upload file to website, call Python script and download a generated new file in the most lighweight way

I need to solve a problem where I parse a csv file via a Python script and generate a new file. I've written the script, but the tricky part is that the file to be handled needs to be uploaded via a browser and the result downloaded likewise. The idea is that it shouldn't require a webserver, it needs to be something like a folder, where you open index.html, upload a file and get a download prompt for the result and I'm looking for the most lightweight solution (I am aware I could do this with Django or Flask, but a whole framework for a tiny tool seems overkill).