What problem does it solve? Python programs often handle external data with ad-hoc mappers, raw json.loads dicts, and try/except blocks that manufacture unproven values. This Skill enforces a disciplined architecture where every boundary crossing uses one of three declarative Pydantic constructs, eliminating hand-written translation and error-handling code. ## Core Features & Use Cases - Foreign Model: Defines frozen BaseModels with Field aliases, validation_alias, and AliasPath to lift another system's data shape into domain types in one constructor call. - Contract Model: Defines frozen BaseModels for the program's own API requests and replies, composed only of declared domain types with no foreign aliases. - Ordered Union: Uses Annotated unions with union_mode="left_to_right" and a TypeAdapter constructor to model foreign data that may fail, replacing try/except defaults and reply parsers. - Use Case: When integrating a trading venue's WebSocket feed, define a VenueFill foreign model with aliases for the venue's keys and an ordered union Frame type that admits unparseable frames as declared values instead of catching exceptions. ## Quick Start Ask the AI to model an incoming API payload or outgoing response shape using the foreign model, contract model, or ordered union constructs from this Skill.
