Enthought Traits
A reference on Dr Dobbs Python-URL pointed me to Enthought Traits, which look very interesting.
This sort of idea crops up all over the place, but is rarely as well focused. This is part, for example, of Plone’s Archetypes and of Nevow’s Formless.
It’s good to see it separated from the persistence machinery (a fault of Archetypes IMO), and good to see the separation of “View” and “Typing and Validation” (a fault of Formless IMO). This is quite a specific set of responsibilities that Trait’s provide, and they seem to be well factored.