For Python's None object, the type hint None is used instead of its actual type, NoneType. From the docs:
Note that None as a type hint is a special case and is replaced by type(None).
I find this confusing and no further explanation is given.
Does anyone know the reason behind this?
It's just a design choice. There's no particular reason behind it.
Writing def fn(x: None) -> None is more concise than def fn(x: NoneType) -> NoneType (and IMHO also clearer).
It's also consistent with other type hints: List, Dict, etc, which are all a single word (the same as the associated built-in function) with an uppercase first letter.
