Python Data Shapes

Use this when the question is which container should carry a piece of domain data and how it should cross wire boundaries.

Working stance

• Pick the lightest container that carries the invariants you need.
• Domain objects belong in immutable, slotted containers; wire payloads belong in validated schema types; dictionaries belong only at serialization boundaries.
• Treat construction as the only place where invariants are checked; trust the type elsewhere.
• For JSON/MessagePack/YAML/TOML, parse to a schema type at the boundary and never let the raw dict leak inward.

Decision surface