Adding type hints to Python has increased my productivity by at least a factor of 10. They allow you to reason about code in a local function without having to track back up dozens of call sites to ensure you're getting what you think you're getting. That alone is worth the price of admission. Both when editing code or reviewing someone else's. It's fantastic, particularly in a very large code base.

The editor experience only increases that factor as you can navigate a lot more freely. Even for small code bases type hints are a revelation. Knowing if something is nullable or not, alone, has caught 100's of bugs in waiting.

Most of the complaints here feel like attacking a strawman, particularly the ones arguing what's the point if you're not running mypy. Run mypy! It's like saying what's the point of writing unit tests if you don't run the test suite. For any sufficiently large code base you absolutely should be running mypy with any plugins for your framework of choice added.

For heterogeneous dictionaries use `dict[str, object]` and then you're forced to use the existing duck-typing mechanisms you're used to. Or, you refactor into better types and/or structures.

Is there friction? Sometimes. You don't have to annotate everything. If the cost is too prohibitive for a particular structure or function, ignore it. Sometimes there are mypy bugs that make writing correct code impossible. # type: ignore[reason] that sucker. Don't throw the baby out with the bath water.

We use a flake8 linter to enforce that all new or modified functions at least annotate their return type which makes interacting with functions quite a bit nicer, and encourages all devs to at least do the minimum. Usually you find that most args are appropriately typed at the same time.