PyO3 Usage Notes

Why we take self_: PyRef<'_, Self>

Most of the Python-facing structs are declared with #[pyclass(extends = ...)]. The actual data (for example the processor field in PyPostProcessor) lives in the base class, while the derived Rust structs are often just markers so that Python sees a proper subclass. When we implement a method on the subclass, we still need to reach into the base storage without downcasting a PyAny or re-wrapping objects.

Using self_: PyRef<'_, Self> gives us a borrowed reference to the Python-owned value that keeps the GIL lifetime, reference counts, and the inheritance chain intact. With it we can call self_.as_ref() to view the base PyPostProcessor directly and access shared helpers like the processor getters/setters. If we used a plain &self we would only see the zero-sized derived struct and would have to convert through a super type just to touch the processors, which adds boilerplate and loses the link to the Python inheritance model. This is the PyO3 equivalent of Python’s super()—it keeps the Rust type information while letting us operate on the underlying parent.