> Yes, but it is bit larger than my single tuple idea in most cases.

Yes, but the code for creating a dict can be simpler. In any case we will better see what format is better when try to write a code.

> I am not sure this is the best option because there are many code object without annotation.

In this case it can be None or NULL.

I like your idea. It is easy to implement it now. Later we can make annotations an attribute of the code object.