What PEP 484 was standardize the use of annotations as type annotations and provide ancillary out-of-the-box support for type hinting via annotations, particularly the typing module.
Mypy was actually using python 3.x annotation for type annotations before PEP 484 standardized them brought the stdlib typing module, but with PEP 484 there was a common, language-defined standard baseline for mypy and other efforts.
Maybe your IDE experience is different than mine, but a typed function will gladly accepted an untyped var without complaining, and during runtime could care less.
Why should type annotation be enforced at run time? In statically typed languages there is no type checking at run time, your type system already proved the type of variable.
> That’s why, for example, they can’t be used to increase the performance of the interpreter.
They can (as in - there's API for that, the rest is up to a community effort) improve performance of a final program, if type-annotated code is passed through Cython with ``annotation_typing=True`` flag:
The annotations are a language syntax feature than the runtime doesn't enforce. There are a number of separate static typecheckers, such as mypy, that do allow AOT static verification (which is, after all, all languages like Haskell have; runtime enforcement of types that have been statically verified in advance isn't super common or necessary.)
