Enums & validated models

Two everyday data-modelling patterns close out the pillar. An enum replaces a scatter of magic strings with a small, closed set of named members — safer, self-documenting, and impossible to mistype. A validated model applies the "parse, don't just store" principle: data is checked and normalised at the boundary, so the rest of your program only ever sees valid values (the idea behind libraries like pydantic).

Modelling states as an Enum and inputs as validated value objects is the quiet backbone of a robust codebase — it's what lets everything downstream stop re-checking the same conditions.