Ask HN: How to go from desktop app to minimum web app

As a side project, I wrote a desktop (python/cython) software application in computer aided engineering. I am trying to turn this desktop application into a bootstrapped SaaS company. I am a mechanical engineer by trade, so my knowledge of web frameworks is negligible.

For the minimum product, I need to have a way to create an account and accept payment. Once logged in I would like the user to be able to upload a file, have the website run the python operation and then return a new file for the user to download (from the python operation). I imagine it might look something like this: https://smallpdf.com/word-to-pdf Additional relevant information, the process currently is relatively process intensive (working on it), currently names in terms of time, so think of it as input file, come back in an hour or the next morning to get result rather than an immediate process.

What are hacker news recommendations for tools/resources for learning to build this minimum viable web product? In terms of languages, I know python (and also C/Fortran) so there is a preference for that, but if another webframe work is superior, I will learn it.