I am confused. "Code gen" is a fuzzy concept once you have a virtual machine because you can do it at runtime. This is how mocking works in Java and C#. What you describe already exists in Java and C# -- decorators for web frameworks. I would not describe Java nor C# as dynamic. I describe them as "stricter" (types) and Python as "weaker" (types). To quote Norman Ramsey: "Every time I see a question about "strong" or "weak" typing, I kill a kitten." :-)