If you want to mainly base your code on the .NET framework, I'd highly recommend IronPython vs Python.NET. IronPython is pretty much native .NET - so it just works great when integrating with other .NET langauges.
Python.NET is good if you want to just integrate one or two components from .NET into a standard python application.
IronPython is written entirely in C#, although some of its code is automatically generated by a code generator written in Python.
Swift <=> Python interop vis PythonKit