Python 3 has optional type hints (and has had them for some time), and some time ago I was a bit tempted to start using some of them; more recently, I wrote a small amount of code using them. Recently I needed to write a little Python program and as I started, I was briefly tempted to try type hints. Then I decided not to, and I suspect that this is how it's going to go in the future.

The practical problem of type hints for me when writing the kind of (small) Python programs that I do today is that they necessarily force me to think about the types involved. Well, that's wrong, or at least incomplete; in practice, they force me to come up with types. When I'm putting together a small program, generally I'm not building any actual data structures, records, or the like (things that have a natural type); instead I'm passing around dictionaries and lists and sets and other basic Python types, and I'm revising how I use them as I write more of the program and evolve it. Adding type hints requires me to navigate assigning concrete types to all of those things, and then updating them if I change my mind as I come to a better understanding of the problem and how I want to approach it.

(In writing this it occurs to me that I do often know that I have distinct types (for example, for what functions return) and I shouldn't mix them, but I don't want to specify their concrete shape as dicts, tuples, or whatever. In looking through the typing documentation and trying some things, it doesn't seem like there's an obvious way to do this. Type aliases are explicitly equivalent to their underlying thing, so I can't create a bunch of different names for eg typing.Any and then expect type checkers to complain if I mix them.)

After the code has stabilized I can probably go back to write type hints (at least until I get into apparently tricky things like JSON), but I'm not sure that this would provide very much value. I may try it with my recent little Python thing just to see how much work it is. One possible source of value is if I come back to this code in six months or a year and want to make changes; typing hints could give me both documentation and guardrails given that I'll have forgotten about a lot of the code and structure by then.

(I think the usual advice is that you should write type hints as you write the program, rather than go back after the fact and try to add them, because incrementally writing them during development is easier. But my new Python programs tend to sufficiently short that doing all of the type hints afterward isn't too much work, and if it gets me to do it at all it may be an improvement.)

PS: It might be easier to do type hints on the fly if I practiced with them, but on the other hand I write new Python programs relatively infrequently these days, making typing hints yet another Python thing I'd have to try to keep in my mind despite it being months since I used them last.

PPS: I think my ideal type hint situation would be if I could create distinct but otherwise unconstrained types for things like function arguments and function returns, have mypy or other typing tools complain when I mixed them, and then later go back to fill in the concrete implementation details of each type hint (eg, 'this is a list where each element is a ...').