For a personal project I am currently using this approach and can confirm it works great.
I wrote just enough PyObjC to get myself a trayicon in the Mac menu bar, which shows a popover containing a wkwebview to localhost. Then I have all the app logic in Python, exposed to the webview through a bottle server, and Svelte for the UI. Highly recommended.
It sounds like a macOS app, and python is distributed with the OS already. Just watch out for Apple trying to take away scripting language support in the future. There's also an upcoming Python version change in macOS 10.16 to look out for.
I actually use py2app to bundle the whole virtualenv into an .app file. Worked pretty much out of the box after fiddling a bit with pyenv (you have to build your python version with framework support).
I wrote just enough PyObjC to get myself a trayicon in the Mac menu bar, which shows a popover containing a wkwebview to localhost. Then I have all the app logic in Python, exposed to the webview through a bottle server, and Svelte for the UI. Highly recommended.