Datasette currently has a few API internals that return sqlite3.Row objects. I was thinking about how this might work in the future - if Datasette ever expands beyond SQLite (plugin-provided backends for PostgreSQL and DuckDB for example) I'd want a way to return data from other stores using objects that behave like sqlite3.Row but are not exactly that class.
That still doesn’t explain why duck typing is ever a thing beyond “I’m too lazy to write
extends BaseClass”. There’s simply no reason to want it.I already explained it to you: protocols apply to types you do not own or control, let alone can specify a base class.
You just specify a protocol, specify that a function requires it, and afterwards you can pass anything to it as-is and you’ll be able to validate your calls.
and I already explained that
Unionis a thing.I’m not sure you understand that what a union does or does not do is completely irrelevant and besides the point. Python’s protocols add support for structural subtyping, and enable both runtime and build-time type checks without requiring major code changes. Don’t you understand what that means?