I created some new models in a system powered by Odoo v12, using its point-and-click interface. I also added some new attributes to existing models, which were created by apps from the marketplace.

How can I export these models and tweaks to a file, preferably in the form of Python code?

I got as far as I could using the GUI, but now that my custom logic is getting more complex, I need the flexibility  one gets when writing actual code. I would prefer to avoid duplication of effort, but I didn't find any export capabilities in the interface.