I started writing an application in Python, but I now want to switch to C# and UWP. I know that you cannot write a UWP app in Python, but I am trying to see if I can write some code in Python and access that code from C#.

For example, writing a class in Python that C# code can access as well. Is that possible? And if so, can Python access Microsoft's UWP APIs?

The main code will not be written in Python; that would be impossible. But can interoperability between C# and Python exist, perhaps with IronPython (.NET's Python)?

And how would I set up such a Visual Studio project? I have Python Tools for Visual Studio installed, but there was no built-in option to add a Python file to my UWP app.

'Classic' python interpreters in c# (as IronPython) don't work in store apps because of framework restrictions, as you run your app through a sandbox.

Some dude has ported the full python interpreter to WinRT on mercurial. Of course, due to framework restrictions, the whole standard library isn't available. This works with WinRT, so it will very likely work on UWP.