Type hints and annotations do provide attributes (see typing.get_type_hints) that can be passed by 3rd party tools but native CPython will not type check these at runtime, so this should not affect the code performance significantly in the same way that comments don't. I ran some tests with timeit and removing type hints had a negligible effect (not distinguishable from the background noise) on the run time, so any concerns about performance would certainly be a severe case of premature optimization.
From PEP 484:
While the proposed typing module will contain some building blocks for
runtime type checking -- in particular the get_type_hints() function
-- third party packages would have to be developed to implement specific runtime type checking functionality, for example using
decorators or metaclasses. Using type hints for performance
optimizations is left as an exercise for the reader.
