We certainly *could* do that. However, I haven't seen sufficient other uses of annotations. If there is only one use for annotations (going forward), annotations would be unambiguous. If we allow different types of annotations, there would have to be a way to tell whether a particular annotation is intended as a type annotation or not. Currently mypy ignores all modules that don't import typing.py (using any form of import statement), and we could continue this convention. But it would mean that something like this would still require the typing import in order to be checked by mypy:

import typing

def gcd(int a, int b) -> int:

    <tralala>

The (necessary) import would be flagged as unused by every linter in the world... :-(

--
--Guido van Rossum (python.org/~guido)