A builder pattern and decorators.

Yes, Python has decorators, but they're best used as "filters" that apply to functions or methods. Cache this, serialize the output of this function always, prepare this function to be used as a tool by an agentic harness. Not registration, not flow control. You may disagree but someone has to say it; FastAPI influenced the modern use of decorators far too much in the wrong direction.

Builder patterns are a Rust convention, because Rust has no named keyword arguments. A Python function already exposes a named contract. There is very little reason to ever to sequentially pass configuration parameters in chained method calls. If you need to add state that doesn't exist yet to a constructor or factory, that is not a builder pattern. That is registration. The one place where builder patterns should be tolerated is query builders. They iteratively build on a concept and having the additional "slot" for metadata (method name plus keyword arguments) is genuinely useful. Using methods which accept single parameter instead of keyword arguments is incorrect.