I think you have misunderstood the point of the ANTLR project. ANTLR is a parser generator, which means roughly:
- You create a grammer for a language of your choosing. This could well be python, or a hybrid of it.
- You run it through ANTLR which gives you code in a number of Languages capable of parsing your language.
This is useful in generating custom scripting languages and the natural language processing domain, both of which are (effectively) related.
Your problem sounds more like you are trying to generate some python code to model a business situation for an enterprise application (loathe as I am to use that term). Rather than reinvent the wheel I suggest you take a look at existing frameworks for achieving this such as SQLAlchemy and Django, both of which provide a base ORM implementation and allow you to derive subclasses which represent your data and include processing logic.
If you are looking for a solution to generate this for you from a description such as UML, I am sure someone is trying to do this too.