It's nonsense that happens to not raise an exception. Typical use would look more like this: x: list[int] = [] i.e. x is a list of integers that starts out

It's nonsense that happens to not raise an exception. Typical use would look more like this: x: list[int] = [] i.e. x is a list of integers that starts out empty. It doesn't automatically do anything at runtime, it's basically a glorified comment for tools and libraries to use. So that does make it harder to figure out what it is.