> Usually, I would mess around in IPython / Jupyter for a couple days until I have something I'm happy with. Then I'll "productionize" the project.

Right, it's this. I get the feeling a lot of people here don't work that way though. I mean I can understand why in a sense, because if you're doing something for your job where your boss says "the project is X" then it's natural to start with a project structure for X. But when I'm going "I wonder if this will work..." then I want to start with the code itself and only "productionize" it later if it turns out to work.