At 65% of developers using it at least sometimes, it seems surprisingly widespread.

Now obviously this survey is going to be somewhat self selected among devs that like to keep up to date and try new things, but 65% having used it in some capacity is pretty comparable to Typescript: https://2019.stateofjs.com/javascript-flavors/typescript/

I treat it as a form of documentation, a step up from docstrings, with the nice touch some tools can actually test it.

I started adding type hints to some Python code the other day and something in my brain was like, "WTF!? Just use Haskell!"

When you add types to Python code it tends to destroy the elegance and readability of it, which is Python's main advantage over other languages.

If you're paying the overhead of adding type information already, you might as well use a language like Haskell that makes it first class and unlocks a ton of power and elegance (and convenient tooling.)

Python has a sweet spot but IMO explicit typing draws it away from that. Python is a very complicated and sophisticated semantics that acts like a simple and easy semantics. It's a delicate balance.

I’m trying to use them more and they are helpful but they can be tedious because now I sometimes have to remember to import the right typing modules and I’m not very comfortable with typed sequences or union types. Anyone have a good cheat sheet or reference?

I’m adding them to code I’m refactoring and it definitely helps there. Instead of a random named variable I can now get completions for the thing I’m working on and dependencies are a lot easier to see and use.