You can even benefit from it without bothering with the type annotations (though they make it more effective).

https://google.github.io/pytype/

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.

> but a typed function will gladly accepted an untyped var without complaining

this can be made prohibited by MyPy's --strict flag [1], and enforced with a mypy git pre-commit hook locally, and with a MyPy CI job.

[1] https://mypy.readthedocs.io/en/stable/command_line.html#cmdo...

That's a mypy setting

There is type inference in all of the Python type checkers, it's not necessarily an "untyped" var because it lacks an annotation.

Running a type checker in Python is a way to avoid runtime type errors, just like in compiled languages, but without a performance benefit.