One of the core concepts of Application Development, (not just in python), is the separation between the Business Logic and the User Interface. However there is a strong temptation to start with the user interface and add the business logic to it some methodologies emphasize this with the process of prototyping the (G)UI first. The danger is that your business logic code can get too entangled with the UI and a change of platform or framework becomes almost impossible. This presentation will show how to maintain a clear separation between the Business Logic and the User Interface by starting with a command line interface using argparse and growing a GUI on top. We will cover: - Why maintain the seperation - Using argparse - Adding a GUI layer with wxPython - Automating the GUI generation - Adding a web interface - Testing advantages of this approach - Scripting advantages - Some packaging models.