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> The desired type is known; it's "Addable" (i.e., "doesn't throw an exception when the built-in add operator is used"). The mistake both you and the reddit po

by mjr00 1y ago

> The desired type is known; it's "Addable" (i.e., "doesn't throw an exception when the built-in add operator is used"). The mistake both you and the reddit posts' author make is treating the `+` operator the same as you would an interface method. Despite Python having __add__/__radd__ methods, this isn't true, nor is it true in many other programming languages. For example, Go doesn't have a way to express "can use the + operator" at all, and "can use comparison operators" is defined as an explicit union between built-in types.[0] In C# you could only do this as of .NET 7, which was released in Nov 2022[1] -- was the C# type system unusable for the 17 years prior, when it didn't support this scenario? If this were any operation on `a` and `b` other than a built-in operator, such as `a.foo(b)`, it would be trivial to define a Protocol (which the author does in Step 4) and have everything work as expected. It's only because of misunderstanding of basic Python that the author continues to struggle for another 1000 words before concluding that type checking is bad. It's an extremely cherry-picked and unrealistic scenario either from someone who is clueless, or knows what they're doing and is intentionally being malicious in order to engagement bait.[2] This isn't to say Python (or Go, or C#) has the best type system, and it certainly lacks compared to Rust which is a very valid complaint, but "I can't express 'type which supports the '+' operator'" is an insanely esoteric and unusual case, unsupported in many languages, that it's disingenuous to use it as an excuse for why people shouldn't bother with type hinting at all. [0] https://pkg.go.dev/cmp#Ordered https://pkg.go.dev/cmp#Ordered [1] https://learn.microsoft.com/en-us/dotnet/standard/generics/math https://learn.microsoft.com/en-us/dotnet/standard/generics/m... [2] actually reading through the reddit comments, the author specifically says they were engagement baiting so... I guess they had enough Python knowledge to trick people into thinking type hinting was bad, fair enough!

pdonis 1y ago
> treating the `+` operator the same as you would an interface method In other words, you agree that the Python type hint system does not give you a good, built-in way to express the "Addable" type. Which means you are contradicting your claims that the type the article wants to express is "unknown" and that the article is advocating using "Any" for this case. The type is not unknown--it's exactly what I said: "doesn't throw an exception when using the + operator". That type is just not expressible in Python's type hint system in the way that would be needed. And "Any" doesn't address this problem, because the article is not saying that every pair of objects should be addable. > "I can't express 'type which supports the '+' operator'" is an insanely esoteric and unusual case I don't see why. Addition is a very commonly used operation, and being able to have a type system that can express "this function takes two arguments that can be added using the addition operator" seems like something any type system that delivers the goods it claims to deliver ought to have. > unsupported in many languages Yes, which means many languages have type systems that claim to deliver things they can't actually deliver. They can mostly deliver them, but "mostly" isn't what advocates of using type systems in all programs claim. So I think the article is making a useful point about the limitations of type systems. > it's disingenuous to use it as an excuse for why people shouldn't bother with type hinting at all. The article never says that either. You are attacking straw men.
- mjr00 1y ago
  > I don't see why. Addition is a very commonly used operation, and being able to have a type system that can express "this function takes two arguments that can be added using the addition operator" seems like something any type system that delivers the goods it claims to deliver ought to have. If your comparison is Rust, sure, but you can't even express this in Java. No, Java's type system is not great, but it's a type system that's been used for approximately 500 trillion lines of production code powering critical systems and nobody has ever said "Java sucks because I can't express 'supports the + operator' as a generic type". (It sucks for many other reasons.) Again, it is factually and objectively an esoteric and unusual case. Nobody in the real world is writing generics like this, only academics or people writing programming blogs about esoterica. If your argument is that all type systems are bad or deficient, fine, but calling out Python for this when it has the exact same deficiency as basically every other mainstream language is asinine. > The article never says that either. You are attacking straw men. The article says "Turning even the simplest function that relied on Duck Typing into a Type Hinted function that is useful can be painfully difficult." The subterfuge is that this is not even remotely close to a simple function because the type being expressed, "supports the + operator", is not even remotely close to a simple type.
  - pdonis 1y ago
    > it is factually and objectively an esoteric and unusual case. Sorry, but your unsupported opinion is not "factual and objective". > If your argument is that all type systems are bad or deficient I said no such thing, any more than the article did. Again you are attacking a straw man. (If you had said "limited in what they can express", I might buy that. But you didn't.) I think I've said all I have to say in this subthread.
    - mjr00 1y ago
      It's factual and objective that billions, if not trillions of lines of Java and Go have been deployed and the language still cannot express "supports the + operator" as a type constraint. In production, non-academic settings, people don't generally write code like that. Again, this is an esoteric limitation from the perspective of writing code that runs working software, not a programming language theory perspective.

by mjr00 1y ago

pdonis 1y ago

> treating the `+` operator the same as you would an interface method In other words, you agree that the Python type hint system does not give you a good, built-in way to express the "Addable" type. Which means you are contradicting your claims that the type the article wants to express is "unknown" and that the article is advocating using "Any" for this case. The type is not unknown--it's exactly what I said: "doesn't throw an exception when using the + operator". That type is just not expressible in Python's type hint system in the way that would be needed. And "Any" doesn't address this problem, because the article is not saying that every pair of objects should be addable. > "I can't express 'type which supports the '+' operator'" is an insanely esoteric and unusual case I don't see why. Addition is a very commonly used operation, and being able to have a type system that can express "this function takes two arguments that can be added using the addition operator" seems like something any type system that delivers the goods it claims to deliver ought to have. > unsupported in many languages Yes, which means many languages have type systems that claim to deliver things they can't actually deliver. They can mostly deliver them, but "mostly" isn't what advocates of using type systems in all programs claim. So I think the article is making a useful point about the limitations of type systems. > it's disingenuous to use it as an excuse for why people shouldn't bother with type hinting at all. The article never says that either. You are attacking straw men.

mjr00 1y ago
> I don't see why. Addition is a very commonly used operation, and being able to have a type system that can express "this function takes two arguments that can be added using the addition operator" seems like something any type system that delivers the goods it claims to deliver ought to have. If your comparison is Rust, sure, but you can't even express this in Java. No, Java's type system is not great, but it's a type system that's been used for approximately 500 trillion lines of production code powering critical systems and nobody has ever said "Java sucks because I can't express 'supports the + operator' as a generic type". (It sucks for many other reasons.) Again, it is factually and objectively an esoteric and unusual case. Nobody in the real world is writing generics like this, only academics or people writing programming blogs about esoterica. If your argument is that all type systems are bad or deficient, fine, but calling out Python for this when it has the exact same deficiency as basically every other mainstream language is asinine. > The article never says that either. You are attacking straw men. The article says "Turning even the simplest function that relied on Duck Typing into a Type Hinted function that is useful can be painfully difficult." The subterfuge is that this is not even remotely close to a simple function because the type being expressed, "supports the + operator", is not even remotely close to a simple type.
- pdonis 1y ago
  > it is factually and objectively an esoteric and unusual case. Sorry, but your unsupported opinion is not "factual and objective". > If your argument is that all type systems are bad or deficient I said no such thing, any more than the article did. Again you are attacking a straw man. (If you had said "limited in what they can express", I might buy that. But you didn't.) I think I've said all I have to say in this subthread.
  - mjr00 1y ago
    It's factual and objective that billions, if not trillions of lines of Java and Go have been deployed and the language still cannot express "supports the + operator" as a type constraint. In production, non-academic settings, people don't generally write code like that. Again, this is an esoteric limitation from the perspective of writing code that runs working software, not a programming language theory perspective.