The pythonOCC development team recently included the excellent SalomeGEOM library from Fotios Sioutis. This have made possible to add parametric modeling feature to pythonOCC. The power of python programming let then the user interact with the geometry from an interactive session, by just modifying the parameters that drive the geometry. I uploaded to youtube a screencast of the simpliest sample I could do to show the concept: a parametric box (parameters being length, depth and height). Have a look to: http://www.youtube.com/watch?v=ZUCv7COgzU0
This feature is still in development but a public release should be soon available.