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I disagree. On the other side is static languages adding things such as "auto" and other ways to automate trivial tasks. Type annotations in dynamic languages i

I disagree. On the other side is static languages adding things such as "auto" and other ways to automate trivial tasks. Type annotations in dynamic languages is the flip-side, trying to reach this "ideal middle" from the other end. What's great with Python type annotation is that you can give it as much as you want, and it'll do the best it can with that. If you don't want to give it any type, then don't. If you want to give type for one function, then only do for that. You get to choose how deep down the well you wan to go.

pkolaczk 7y ago
I disagree. Type inference in statically typed languages (e.g. auto or var) does not weaken static typechecking guarantees. So it is not the same as writing type annotations only as much as you want. It is stronger.
- ehsankia 7y ago
  I never said it weakens it, but it's trying to keep the strong type checking while making the language easier. Python is the opposite, it's easy to write but doesn't have the strong guarantees, and it's trying to become safer while keeping the ease of writing. This ideal "middle state" I speak of is a language that is both as easy as a dynamic language but as safe as a static language. Static languages are making it easier to write and dynamic languages are making it safer.
  - humanrebar 7y ago
    If you limit the model to source code diagnostics, you have a good point. But statically typed languages also use the types for other things: optimization, generic code instantiation, symbol resolution, and even certain kinds of metaprogramming. Optional type checking is a nice way to reduce certain kinds of errors and tighten up some underspecified designs, but it falls very much short of actual static type checking. That being said, most of the unique things static typing provides aren't needed for typical CRUD apps and glue logic, so type annotated python isn't a bad choice.
    - ehsankia 7y ago
      The way Python's type checking is implemented (it's literally just annotations) it can be used for all of the above. There are already libraries that existed before where you can accelerate specific functions, like Numba. Those libraries could switch to using type annotations instead. Similarly, IDEs are already use type annotations to enhance their symbol resolution and so on. Lastly, I'm not sure what you mean by "falls very much short of actual static type checking". With mypy and PyType, you can already catch many bugs that you wouldn't have otherwise, without running the code. That's the definition of static type checking. It may not do as much as c++, but it still catches significantly more than most other pure dynamic languages with no type.
      - humanrebar 7y ago
        There are other implications, but binary linking is fraught. Minor errors corrupt entire executables, systems, and data stores, including entirely unrelated subsystems. Often statically typed systems use (at the binary level!) type information to trade off defensiveness (checking that array indexing is in bounds, maybe) for other things (latency, throughput, etc.). Point being, the type information is used for more things than just telling coders about API mismatches. Maybe some libraries could use type information to dynamically use better code paths, but statically typed languages use this information far before that... when the equivalent of a wheel is created, for instance.
  - pkolaczk 7y ago
    Easier to learn != easier to write. For a person like me who has learnt a few languages with static type systems like Scala or C++ first, which are also arguably harder to learn than Python, it is easier to write and read Scala or C++ than Python. This is because static type annotations serve as documentation and they enable various helpful IDE features like code completion, find usages, safe refactoring, real time correctness checking etc. These features work best when the type information is complete. For some of the projects I had to use JS / Python / PHP and I find writing these much harder. Indeed, it was very easy to learn the core of the language, but then not having reliable IDE support made writing the actual code (and using libraries or digging into existing code) slower.
    - zo1 7y ago
      If you didn't have reliable IDE support while developing python then you didn't use a good IDE or the code you were working with had too much dynamic voodoo nonsense. One must never go "full dynamic", because you then get the worst of both worlds. I've generally had reliable IDE support for python for almost a decade now. First in the form of PyDev on Eclipse, and now PyCharm.
      - pkolaczk 7y ago
        IMHO PyCharm is good among dynamic languages, but it's still far from the level of IDE support you get for statically typed languages. It is very conservative in the number of bugs it highlights. Same problem in VSCode and JS. While autocomplete is quite nice and works most of the times, they fail to catch most problems when I type.
rebeccaskinner 7y ago
This isn't the first time I've seen this argument- clearly there are people that it rings true for, but I just have a hard time seeing it. The benefits you get from types start to very quickly diminish as soon as you start adding untyped values into the mix. Sure, there are the odd cases where you might happen to have a typed function and a typed value and the checker can find a bug for you, but my experience writing python tells me these cases in reality are vanishingly rare. And the cost of this flexibility seems to be quite high. The overall quality of type checking that mypy gives you seems to be pretty abysmal, and it requires quite a bit more handholding and awkward workarounds to deal with the proliferation of any's and uninferable types than a language that just starts with types in the first place.
- ehsankia 7y ago
  Not really. Enable something like MyPy or PyType on a big enough codebase with zero explicit annotation and it'll already find plenty of bugs and unhandled cases from the inferred types alone. Some of these are stuff a strong IDE may catch too (using the wrong function name, passing wrong number of args, etc), but some other ones are actually deeper in the code. So already, with zero annotations, you already get value out, let alone once you type a few tricky variables that are harder for Python to track.
  - rebeccaskinner 7y ago
    I've never seen that personally, but most of my python work has been on small to medium sized projects (generally in the 5-10 KLOC range).
    - nl 7y ago
      What kind of "untyped data" are you dealing with?
- Too 7y ago
  That's like saying the value of unit tests quickly diminish once you add non tested code to the mix. For fearless refactoring, sure, you need quite high type-coverage to not get a false sense of security, but still, the more you have the safer it is. For just finding bugs and code navigation, any addition of types is going to be a win.
umanwizard 7y ago
`auto`, type inference, etc. has nothing to do with dynamic types. The types are still 100% static, not some sort of compromise or middle ground between static and dynamic.
- ehsankia 7y ago
  You missed my point. Static languages try to make it easier to use, while dynamic languages try to become safer. They each try to keep what makes their side good, while getting some hints of what the other side has.
  - umanwizard 7y ago
    I guess I didn’t understand your point because I think statically typed languages are more easy to use than Python, not less, as soon as the program is longer than 500 lines or so.
    - ehsankia 7y ago
      Right, but in python, especially with use of the third party libraries, I can glue together something using less than 20 lines of code. I once had a script that recorded the microphone, converted the waveform, passed it to TTS to turn it to text, translated it, then converted it back into audio and played it. All with under 30 lines of Python. Meanwhile with C++, just trying to manipulate some strings will take that many lines. I guess we have different definition of "easy to use".
      - umanwizard 7y ago
        C++ is not the only statically-typed language. Can you elaborate on why Python's lack of type checking specifically (as opposed to any of the other ease-of-use features of Python) made it easier for you to write this program? Were there cases where you were using something that a statically typed language would have considered the "wrong" type for a function argument (or anything else), but it worked fine in Python?
zozbot234 7y ago
> What's great with Python type annotation is that you can give it as much as you want That's also what's Not Great about this whole 'annotation' or 'gradual typing' approach. Having only some arbitrary part of the program be statically typed introduces a huge amount of 'interaction' or 'blame' points between the static and the dynamic portion of your program, that significantly impact the usual benefits of static typing. Dynamic types should be used only when strictly necessary, everything else should be made static as soon as feasible.
- joshuamorton 7y ago
  Hard disagree: interfaces should be statically typed, but implementations need not be unless it adds value. Languages like python with a typechecker are much closer to rust (safe, but with the ability to have unsafe areas) than true statically typed langs, because static languages don't give easy escape hatches (you end up having to cast everything, no static Lang I'm aware of ships with an Any type like python's).
  - _jsdw 7y ago
    Rust is a true statically typed language; `unsafe` in rust relates to code that violates memory safety guarantees, but you can't escape the static type checking using it. Rust actually has an `Any` trait which allows for a certain amount of runtime type asserting if you don't know what concrete type you'll be working with.
    - joshuamorton 7y ago
      This is a mostly semantic distinction. Rust provides safety guarantees, but you're able to opt out of some of those in certain well defined ways.
  - colatkinson 7y ago
    Never actually seen it used, but: https://en.cppreference.com/w/cpp/utility/any https://en.cppreference.com/w/cpp/utility/any
  - 7y ago
ibejoeb 7y ago
Sounds like a good rationalization. I really think it's hinting for an IDE so that it knows where and when UDTs are used. The cool thing about python is that the stdlib is readily memorizable. It's a little idiomatic, but it's relatively small. The onus is on the IDE--if you want one--to be smart. Type hinting probably doesn't catch many bugs, especially with metaprogramming, but it might add some value to large codebases or team development.

pkolaczk 7y ago

I disagree. Type inference in statically typed languages (e.g. auto or var) does not weaken static typechecking guarantees. So it is not the same as writing type annotations only as much as you want. It is stronger.

ehsankia 7y ago
I never said it weakens it, but it's trying to keep the strong type checking while making the language easier. Python is the opposite, it's easy to write but doesn't have the strong guarantees, and it's trying to become safer while keeping the ease of writing. This ideal "middle state" I speak of is a language that is both as easy as a dynamic language but as safe as a static language. Static languages are making it easier to write and dynamic languages are making it safer.
- humanrebar 7y ago
  If you limit the model to source code diagnostics, you have a good point. But statically typed languages also use the types for other things: optimization, generic code instantiation, symbol resolution, and even certain kinds of metaprogramming. Optional type checking is a nice way to reduce certain kinds of errors and tighten up some underspecified designs, but it falls very much short of actual static type checking. That being said, most of the unique things static typing provides aren't needed for typical CRUD apps and glue logic, so type annotated python isn't a bad choice.
  - ehsankia 7y ago
    The way Python's type checking is implemented (it's literally just annotations) it can be used for all of the above. There are already libraries that existed before where you can accelerate specific functions, like Numba. Those libraries could switch to using type annotations instead. Similarly, IDEs are already use type annotations to enhance their symbol resolution and so on. Lastly, I'm not sure what you mean by "falls very much short of actual static type checking". With mypy and PyType, you can already catch many bugs that you wouldn't have otherwise, without running the code. That's the definition of static type checking. It may not do as much as c++, but it still catches significantly more than most other pure dynamic languages with no type.
    - humanrebar 7y ago
      There are other implications, but binary linking is fraught. Minor errors corrupt entire executables, systems, and data stores, including entirely unrelated subsystems. Often statically typed systems use (at the binary level!) type information to trade off defensiveness (checking that array indexing is in bounds, maybe) for other things (latency, throughput, etc.). Point being, the type information is used for more things than just telling coders about API mismatches. Maybe some libraries could use type information to dynamically use better code paths, but statically typed languages use this information far before that... when the equivalent of a wheel is created, for instance.
- pkolaczk 7y ago
  Easier to learn != easier to write. For a person like me who has learnt a few languages with static type systems like Scala or C++ first, which are also arguably harder to learn than Python, it is easier to write and read Scala or C++ than Python. This is because static type annotations serve as documentation and they enable various helpful IDE features like code completion, find usages, safe refactoring, real time correctness checking etc. These features work best when the type information is complete. For some of the projects I had to use JS / Python / PHP and I find writing these much harder. Indeed, it was very easy to learn the core of the language, but then not having reliable IDE support made writing the actual code (and using libraries or digging into existing code) slower.
  - zo1 7y ago
    If you didn't have reliable IDE support while developing python then you didn't use a good IDE or the code you were working with had too much dynamic voodoo nonsense. One must never go "full dynamic", because you then get the worst of both worlds. I've generally had reliable IDE support for python for almost a decade now. First in the form of PyDev on Eclipse, and now PyCharm.
    - pkolaczk 7y ago
      IMHO PyCharm is good among dynamic languages, but it's still far from the level of IDE support you get for statically typed languages. It is very conservative in the number of bugs it highlights. Same problem in VSCode and JS. While autocomplete is quite nice and works most of the times, they fail to catch most problems when I type.

rebeccaskinner 7y ago

This isn't the first time I've seen this argument- clearly there are people that it rings true for, but I just have a hard time seeing it. The benefits you get from types start to very quickly diminish as soon as you start adding untyped values into the mix. Sure, there are the odd cases where you might happen to have a typed function and a typed value and the checker can find a bug for you, but my experience writing python tells me these cases in reality are vanishingly rare. And the cost of this flexibility seems to be quite high. The overall quality of type checking that mypy gives you seems to be pretty abysmal, and it requires quite a bit more handholding and awkward workarounds to deal with the proliferation of any's and uninferable types than a language that just starts with types in the first place.

ehsankia 7y ago
Not really. Enable something like MyPy or PyType on a big enough codebase with zero explicit annotation and it'll already find plenty of bugs and unhandled cases from the inferred types alone. Some of these are stuff a strong IDE may catch too (using the wrong function name, passing wrong number of args, etc), but some other ones are actually deeper in the code. So already, with zero annotations, you already get value out, let alone once you type a few tricky variables that are harder for Python to track.
- rebeccaskinner 7y ago
  I've never seen that personally, but most of my python work has been on small to medium sized projects (generally in the 5-10 KLOC range).
  - nl 7y ago
    What kind of "untyped data" are you dealing with?
Too 7y ago
That's like saying the value of unit tests quickly diminish once you add non tested code to the mix. For fearless refactoring, sure, you need quite high type-coverage to not get a false sense of security, but still, the more you have the safer it is. For just finding bugs and code navigation, any addition of types is going to be a win.

umanwizard 7y ago

`auto`, type inference, etc. has nothing to do with dynamic types. The types are still 100% static, not some sort of compromise or middle ground between static and dynamic.

ehsankia 7y ago
You missed my point. Static languages try to make it easier to use, while dynamic languages try to become safer. They each try to keep what makes their side good, while getting some hints of what the other side has.
- umanwizard 7y ago
  I guess I didn’t understand your point because I think statically typed languages are more easy to use than Python, not less, as soon as the program is longer than 500 lines or so.
  - ehsankia 7y ago
    Right, but in python, especially with use of the third party libraries, I can glue together something using less than 20 lines of code. I once had a script that recorded the microphone, converted the waveform, passed it to TTS to turn it to text, translated it, then converted it back into audio and played it. All with under 30 lines of Python. Meanwhile with C++, just trying to manipulate some strings will take that many lines. I guess we have different definition of "easy to use".
    - umanwizard 7y ago
      C++ is not the only statically-typed language. Can you elaborate on why Python's lack of type checking specifically (as opposed to any of the other ease-of-use features of Python) made it easier for you to write this program? Were there cases where you were using something that a statically typed language would have considered the "wrong" type for a function argument (or anything else), but it worked fine in Python?

zozbot234 7y ago

> What's great with Python type annotation is that you can give it as much as you want That's also what's Not Great about this whole 'annotation' or 'gradual typing' approach. Having only some arbitrary part of the program be statically typed introduces a huge amount of 'interaction' or 'blame' points between the static and the dynamic portion of your program, that significantly impact the usual benefits of static typing. Dynamic types should be used only when strictly necessary, everything else should be made static as soon as feasible.

joshuamorton 7y ago
Hard disagree: interfaces should be statically typed, but implementations need not be unless it adds value. Languages like python with a typechecker are much closer to rust (safe, but with the ability to have unsafe areas) than true statically typed langs, because static languages don't give easy escape hatches (you end up having to cast everything, no static Lang I'm aware of ships with an Any type like python's).
- _jsdw 7y ago
  Rust is a true statically typed language; `unsafe` in rust relates to code that violates memory safety guarantees, but you can't escape the static type checking using it. Rust actually has an `Any` trait which allows for a certain amount of runtime type asserting if you don't know what concrete type you'll be working with.
  - joshuamorton 7y ago
    This is a mostly semantic distinction. Rust provides safety guarantees, but you're able to opt out of some of those in certain well defined ways.
- colatkinson 7y ago
  Never actually seen it used, but: https://en.cppreference.com/w/cpp/utility/any https://en.cppreference.com/w/cpp/utility/any
- 7y ago

ibejoeb 7y ago

Sounds like a good rationalization. I really think it's hinting for an IDE so that it knows where and when UDTs are used. The cool thing about python is that the stdlib is readily memorizable. It's a little idiomatic, but it's relatively small. The onus is on the IDE--if you want one--to be smart. Type hinting probably doesn't catch many bugs, especially with metaprogramming, but it might add some value to large codebases or team development.