[eru]

OK. How is that different from using functions? Conceptually, there's a function that does arbitrary computation under the hood.

(I think we are already agreeing, only that you express your point differently in Python specific terms. I don't care whether you stuff your code into a context object or something else. I was talking about having the full power of the programming language available, vs using a limited language like format strings.)

[cbsmith]

The important part is you have one more level of indirection before you figure out the layout of the message.