NamedTuple subclassing NamedTuple · Issue #427 · python/typing (original) (raw)

I naively thought that since I can write

class A(NamedTuple): x: int y: int

I would also be able to subclass this:

class B(A): z: int

That is accepted syntactically and at runtime but no new __new__ method is generated so calling B(1, 2, 3) is flagged as an error (too many arguments) by both mypy and runtime.