Dataclasses is notable because it's the only example (I'm aware of) of type hints effecting runtime behavior as part of the stdlib.
Compiler instructions: mypyc was (one of?) the first to do this, but Cython actually supports this natively now, and is much more active than mypyc is last I checked.
Runtime behaviour determination: the stdlib [dataclasses](https://docs.python.org/3/library/dataclasses.html#module-da...)
Dataclasses is notable because it's the only example (I'm aware of) of type hints effecting runtime behavior as part of the stdlib.
Compiler instructions: mypyc was (one of?) the first to do this, but Cython actually supports this natively now, and is much more active than mypyc is last I checked.