> it has a higher cost-benefit than anything else that's been tried
I would want to see a lot of data, for a lot of different kinds of programs, to back up this claim.
> So is time you spend thinking about the behaviour of the code in your head
You have to do this anyway; static typing doesn't write your code for you. Even Haskell, which I will freely admit is probably the closest thing to an AI that I've ever seen in a programming language, can't do that. :-)
> your code will almost always be silently unsound
Code that has type annotations has this same problem. That was the point of my response: static typing != sound code.
> libraries you're using will usually have incorrect type annotations
They can't be incorrect if they aren't there. The comparison I'm making is not between code with correct type annotations and code with incorrect ones. It's between code with type annotations and code without any of them at all.
> You have to do this anyway; static typing doesn't write your code for you.
The amount is what matters. If spending x minutes writing down types saves you y minutes of thinking, and y>x, that's a win.
> Code that has type annotations has this same problem. That was the point of my response: static typing != sound code.
Well-typed code has certain soundness properties - they may not fully encode all the properties you want your program to have (that part is up to you), but the properties that you have encoded will be reliable. Optional typing undermines that: even if the types say one thing, you have no guarantee that that thing is true.
> They can't be incorrect if they aren't there. The comparison I'm making is not between code with correct type annotations and code with incorrect ones. It's between code with type annotations and code without any of them at all.
My point is that if the ecosystem is not well-typed then you don't actually have the choice of using types. What I'm arguing against is your claim that Python gives you the choice: it doesn't, because to be able to write well-typed code you need well-typed libraries.
> > So is time you spend thinking about the behavior of the code in your head
> You have to do this anyway; static typing doesn't write your code for you. Even Haskell, which I will freely admit is probably the closest thing to an AI that I've ever seen in a programming language, can't do that. :-)
I think what he meant to say is that you spent 95% of your time to think about: "what is the kind of think I can from this method call and how can and should I use it and what should I return in the end". Writing down the result of your thoughts takes almost no time in comparison. Not only that, in good statically typed languages, you don't have to write down the types explicitly most of the time (but you can still have your IDE show them to you if you want to see them).
And in addition to that, you certainly have to think _less_ in many cases. A good example are functions that return lists. Often you always have an element in the list. Using a good type-system, it will be indicated, so when I get the list, I know that I don't have to handle the case that the list is empty.
In python I would often have to think _more_ about it and look into the documentation or maybe even the implementation to understand if it could return an empty list or not.
> you spent 95% of your time to think about: "what is the kind of think I can from this method call and how can and should I use it and what should I return in the end". Writing down the result of your thoughts takes almost no time in comparison.
The issue here isn't static vs. dynamic typing, it's API documentation. In cases where static type declarations work out to be sufficient as API documentation, sure, use them as API documentation. But the "time to think" issue isn't being solved by static typing; it's being solved by having good documentation for the APIs you are using (or writing good documentation for the APIs of the libraries you are writing).
> A good example are functions that return lists. Often you always have an element in the list. Using a good type-system, it will be indicated, so when I get the list, I know that I don't have to handle the case that the list is empty.
Same comment here: whether or not the function can return an empty list is part of the API. The API needs to be documented somehow. A static type declaration might be enough, or it might not. Either way, what's solving the issue isn't static typing, it's API documentation.
> Time you spend writing type specifications is time you're not spending doing something else that might add more value.
To what I say: writing out a type (= a few characters) is negligible anyways when compared to the time you spend thinking about what the type is (which you have to do in python as well, maybe even more).
> Same comment here: whether or not the function can return an empty list is part of the API. The API needs to be documented somehow.
If you have a proper API documentation in both cases, then you have to think less, that's true. In the real world however, I can testify that I have to think longer in python because 1) APIs not always well documented and 2) even if they are, a well documented API that uses statical types is still easier to use due to the automatic compiler/IDE support.
> writing out a type (= a few characters) is negligible anyways when compared to the time you spend thinking about what the type is
Writing out a type is only a few characters if it's a type that's already built into your type system. (In which case, as others have already pointed out, you probably won't have to write it anyway in a statically typed language because the type system will automatically infer it. But in such cases, you're not gaining any documentation benefit from it.)
If it's a type you're having to invent as part of writing the code, writing it out everywhere it gets used can be a lot more work.
> I have to think longer in python because 1) APIs not always well documented
Meaning, not well documented compared to APIs in other languages? That hasn't been my experience; my experience has been that API documentation pretty much sucks everywhere.
> a well documented API that uses statical types is still easier to use due to the automatic compiler/IDE support
If you use an IDE, perhaps. (I don't; I find that they cost me more than they save me.)
> Writing out a type is only a few characters if it's a type that's already built into your type system.
Right, but if it is not, then you also have write extra code in python (e.g. create a new class).
Of course alternatively you can also just use "String" for everything (you can do that with a statical typesystem too), but I hope you agree with me that this isn't a great idea in any language.
I also have the feeling that you might change your mind if you try out a modern fully fledged IDE with a good statically typed language. The reason why I think this is because of things that you said such as "But in such cases, you're not gaining any documentation benefit from it." which are correct if you are not using an IDE. But if you do, it's actually wrong. IDEs like IntelliJ can be configured to show all (or only certain) types that are not written in text but that the compiler infers - without pressing any key. I like to use this feature a lot when diving into an unknown code base.
> Meaning, not well documented compared to APIs in other languages?
No, just not being well documented. Many popular libraries in python are well documented, but not all are. And the less popular/public ones are often poorly documented. The same is true for other languages as well, but in those, you at least you often have a "basic" documentation through the types.
> if it is not, then you also have write extra code
In any language, not just Python. A type that isn't already built-in has to be defined in your code no matter what language you are using.
> I hope you agree with me that this isn't a great idea in any language.
Of course it isn't. Different types exist for good reasons.
> I also have the feeling that you might change your mind if you try out a modern fully fledged IDE with a good statically typed language.
I doubt you would have this feeling if you knew how many times I have tried "a modern fully fledged IDE with a good statically typed language". And every time has ended up the same.
> IDEs like IntelliJ can be configured to show all (or only certain) types that are not written in text but that the compiler infers
This is a fair point, but in a language like Python this could be provided as a library function if it were needed. (Python already has the "help" built-in function that shows you the documentation for whatever object you pass it as an argument, at the Python interactive prompt. Inferred types could be handled the same way if Python had them.)
> at least you often have a "basic" documentation through the types
Which might be significant useful information. Or it might not. It depends on what kind of code you are dealing with. It's quite possible that the particular kind of code I have dealt with has simply not been the kind where static typing is much of a help, and that there are other kinds of code where it is. But the original claim that I responded to was "Everyone needs types" (by which was meant "everyone needs static typing"). It is that blanket, general claim that static typing is always better that I was disputing, not the claim that static typing can be helpful in some cases.
> In any language, not just Python. A type that isn't already built-in has to be defined in your code no matter what language you are using.
Yeah exactly! So it's the same for every language. I just don't understand why you then say that I would have to type more in a statically typed language.
> I doubt you would have this feeling if you knew how many times I have tried "a modern fully fledged IDE with a good statically typed language". And every time has ended up the same.
Everyone is different and that's one reason why people choose different tools and languages. Nothing wrong with this - one of the best developers that I know uses vim for everything. I on the other hand would not be productive without a good IDE.
> But the original claim that I responded to was "Everyone needs types" (by which was meant "everyone needs static typing"). It is that blanket, general claim that static typing is always better that I was disputing
Fair enough, I agree with you on that one. The thing I disagree with is that is static typing requires (always) more effort when writing code. For Java this is totally true, but for many other languages, my experience is that I neither have to type more nor that I have to think more.
> If it's a type you're having to invent as part of writing the code, writing it out everywhere it gets used can be a lot more work.
Not really; you write it out fully once, when creating a type alias/definition, and then just use the name later.
> Meaning, not well documented compared to APIs in other languages?
Yeah, I’ve found Python to have a pretty good documentation culture (docstrings especially facilitate this), often better than some statically typed languages with ecosystems where signatures are regularly mistaken for adequate documentation.
> In python I would often have to think _more_ about it and look into the documentation or maybe even the implementation to understand if it could return an empty list or not.
In many cases in Python, you don't have to care. For example, if you're going to iterate over the list, Python will iterate over an empty list just fine: it will execute zero iterations. No need to check anything.
Right. I was referring to the cases where you must care, such as presenting a list of errors to someone or doing a calculation where an empty list must be considered in a special way if it occurs etc.
I would want to see a lot of data, for a lot of different kinds of programs, to back up this claim.
> So is time you spend thinking about the behaviour of the code in your head
You have to do this anyway; static typing doesn't write your code for you. Even Haskell, which I will freely admit is probably the closest thing to an AI that I've ever seen in a programming language, can't do that. :-)
> your code will almost always be silently unsound
Code that has type annotations has this same problem. That was the point of my response: static typing != sound code.
> libraries you're using will usually have incorrect type annotations
They can't be incorrect if they aren't there. The comparison I'm making is not between code with correct type annotations and code with incorrect ones. It's between code with type annotations and code without any of them at all.