An interesting pytype experiment, and a possible extension to strings

[NeilGirdhar]

@sirosen

If the type system can express str - Iterable[str]

Did you see this comment? str - Iterable[str] is simply Never.

@sirosen

This makes the most sense in the context of a type-checker flag which starts out with a lenient default, like how no-implicit-optional was handled.

Even if you could define AtomicString, then functions that accept Iterable[T] will continue to accept strings, which is exactly the kind of bug that we are aiming to prevent.