If you are primarily focused on Windows, nothing beats IronPython's power and flexibility, in my opinion.
As a fully functional .NET language, you can easily write powerful applications using WPF (Windows Presentation Foundation) and, as a bonus, interact with any library, class or module that has ever written in any .NET language. Having access to the whole world of .NET collections and getting to write in python, he personally shakes my notorious socks.
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