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This starts off with a misunderstanding of what "strongly typed" means. Python is strongly, but dynamically typed. Static typing means you know the type of som

by lvh 8y ago

This starts off with a misunderstanding of what "strongly typed" means. Python is strongly, but dynamically typed. Static typing means you know the type of something at compile time. Dynamic typing means you don't. The upside to dynamic typing is that the compiler doesn't have to prove much about your program; the downside is that it can't really prove much of interest either. Strong vs weak typing is about how much your language is willing to fudge types in order to make an operation succeed without errors -- be it the intended result or not. Both static and strong typing tend to make errors be more obvious sooner. Both dynamic and weak typing tend to require less boilerplate to make your program do things. Python doesn't know the types of things in advance (dynamically typed), but it is very picky about which types are allowed to interact (strongly typed). Even in cases where the answer is obvious, like str.join, you still have to make everything strings: "".join([1, 2, 3]) will fail. To demonstrate why these are orthogonal, consider the other cases. Haskell is strongly and statically typed. A program that adds a string and a number together will be rejected at compile time because the compiler can prove it's invalid. C is weakly and statically typed. A program that combines a string and a number may be accepted by the compiler, who interprets the number as, I dunno, a wchar_t or something. Another example of weak typing is how C allows (heck, encourages) pointer arithmetic and untagged unions/structs. JavaScript is weakly and dynamically typed. A program that adds a string and a number together will, at runtime, convert the number to a string and then concatenate the two.

tln 8y ago
You're correct but this barely changes the authors points: "It’s virtually impossible to statically analyze" and "In Python a good amount of errors are discovered at runtime"
- lvh 8y ago
  The rest of the points are silly rehashes of arguments as old as Emacs v vim, but sure, let's go there too. We've done empirical research to see if this matters. Charitably, the results are "inconclusive"[0]. > The first glaring issue is that I have no guarantee that is_valid() returns a bool type. You can name functions ridiculous, unhelpful and misleading things in any language. The very fact that you know to expect a bool undermines the point: clearly, despite not having static types, a human managed to make a pretty reasonable assumption about what a piece of code was about to do. Just because the compiler can check that is_valid returns a string doesn't mean that hat's magically a useful thing to do. > The fact that I cannot, in the absence of perfect test coverage, verify the syntactical correctness of someone’s code is a big red flag. Syntax errors are caught by the compiler. Semantic errors aren't caught by the best type systems. At best, type systems are a way to encode a bit of the semantics so that the compiler can prove things about it. > To improve static type checking in Python, developers made libraries like jedi, pytype, mypy, and toasted-marshmallow, but they are often not used in most projects because they do not belong to the standard toolchain I can not imagine the author actually used jedi and believes this. That's... not how jedi works. I also don't know what to do with the argument of "oh, you have an optional static type system but people don't use it because it's annoying, this is why we should use a mandatory static type system" other than shrug. I like types! I think there are great arguments for types. I like the idea of being able to have a type system prove that certain bugs can't happen. This adds nothing but FUD and no new insights. [0]: https://danluu.com/empirical-pl/ https://danluu.com/empirical-pl/
- mlthoughts2018 8y ago
  > “In Python a good amount of errors are discovered at runtime" In my experience this is roughly equally true with statically typed languages as it is with Python. The types of errors the compiler helps find before running tests are just not important. They are not types of errors that matter much. And if compiler errors are cryptic enough, it can be a huge huge pain that you can’t just run the code on a toy input to see what’s going on. The whole pitch about how static typing and compilation will save you time by forcing more correctness prior to testing is just a hogwash myth in practice. It happens occasionally, but not nearly enough to justify all the stuff advocating it, and the benefits of being able to debug according to desired behavior and just not care about strict safety in edge cases you can guarantee you won’t hit are really tangible. You cannot easily dismiss these benefits.
hedora 8y ago
Python objects are duck typed, and c/c++ structs are strongly typed. Duck typing is closer to weak typing than strong typing. Tagged unions are dangerous in C/C++, but python’s object type is strictly weaker than a union. In fact, C and C++ are both strongly typed, but they are both memory unsafe. However, C++ provides enough static typing to make it easy to write memory safe (but single threaded) programs. Also, tools like valgrind get you 99% of the benefit of memory safety, which is good enough for debugging. C++ lets you override the allocator, and build in inexpensive (fast enough for production) checks for most use after frees, memory consumption profilers / leak detection/ etc. I’d argue that python is memory unsafe in practice, since we get segfaults from third party dependencies in python about as often as we see them in c/c++. Crucially, C and C++ provide enough tools to get static type safety on the error handling path. Errors like ‘assert “” is not None’ and missing field exceptions in python error handling code are frequent, but unheard of in C/C++. If you use std::string, adding a in integer does something well-defined (rtfm). Adding an int to a char widens the result to the int type (foiling attempts to use it like a char without a downcast, if you use -Wall -Werror). Adding an into to a char* does pointer arithmetic, which can be used safely, but there are better string / buffer types you can implement in an afternoon, so do that instead.
- lvh 8y ago
  > In fact, C and C++ are both strongly typed, but they are both memory unsafe. You are refuting my point but provide no evidence and implicitly redefine several terms in a way contrary to common usage. Is there a definition you can pen down? Because C sure isn't strongly typed in the Liskov, Jackson or modern usage senses of the term. > Also, tools like valgrind get you 99% of the benefit of memory safety, which is good enough for debugging. C++ lets you override the allocator, and build in inexpensive (fast enough for production) checks for most use after frees, memory consumption profilers / leak detection/ etc. Would you say that de facto C/C++ has a memory safety problem? If it does, why? (Also, not germane to my point.) > I’d argue that python is memory unsafe in practice, since we get segfaults from third party dependencies in python about as often as we see them in c/c++. Do you have extraordinary evidence to go with this extraordinary claim, or are you just talking about your own anecdata? (Also, not germane to my point.) > If you use std::string, adding a in integer does something well-defined (rtfm). My argument was not that it is poorly defined. Weak typing doesn't mean UB.
marcosdumay 8y ago
> I dunno, a wchar_t or something Most likely a char or a * wchar. Yeah, random pointers.

by lvh 8y ago

tln 8y ago

You're correct but this barely changes the authors points: "It’s virtually impossible to statically analyze" and "In Python a good amount of errors are discovered at runtime"

lvh 8y ago
The rest of the points are silly rehashes of arguments as old as Emacs v vim, but sure, let's go there too. We've done empirical research to see if this matters. Charitably, the results are "inconclusive"[0]. > The first glaring issue is that I have no guarantee that is_valid() returns a bool type. You can name functions ridiculous, unhelpful and misleading things in any language. The very fact that you know to expect a bool undermines the point: clearly, despite not having static types, a human managed to make a pretty reasonable assumption about what a piece of code was about to do. Just because the compiler can check that is_valid returns a string doesn't mean that hat's magically a useful thing to do. > The fact that I cannot, in the absence of perfect test coverage, verify the syntactical correctness of someone’s code is a big red flag. Syntax errors are caught by the compiler. Semantic errors aren't caught by the best type systems. At best, type systems are a way to encode a bit of the semantics so that the compiler can prove things about it. > To improve static type checking in Python, developers made libraries like jedi, pytype, mypy, and toasted-marshmallow, but they are often not used in most projects because they do not belong to the standard toolchain I can not imagine the author actually used jedi and believes this. That's... not how jedi works. I also don't know what to do with the argument of "oh, you have an optional static type system but people don't use it because it's annoying, this is why we should use a mandatory static type system" other than shrug. I like types! I think there are great arguments for types. I like the idea of being able to have a type system prove that certain bugs can't happen. This adds nothing but FUD and no new insights. [0]: https://danluu.com/empirical-pl/ https://danluu.com/empirical-pl/
mlthoughts2018 8y ago
> “In Python a good amount of errors are discovered at runtime" In my experience this is roughly equally true with statically typed languages as it is with Python. The types of errors the compiler helps find before running tests are just not important. They are not types of errors that matter much. And if compiler errors are cryptic enough, it can be a huge huge pain that you can’t just run the code on a toy input to see what’s going on. The whole pitch about how static typing and compilation will save you time by forcing more correctness prior to testing is just a hogwash myth in practice. It happens occasionally, but not nearly enough to justify all the stuff advocating it, and the benefits of being able to debug according to desired behavior and just not care about strict safety in edge cases you can guarantee you won’t hit are really tangible. You cannot easily dismiss these benefits.

hedora 8y ago

Python objects are duck typed, and c/c++ structs are strongly typed. Duck typing is closer to weak typing than strong typing. Tagged unions are dangerous in C/C++, but python’s object type is strictly weaker than a union. In fact, C and C++ are both strongly typed, but they are both memory unsafe. However, C++ provides enough static typing to make it easy to write memory safe (but single threaded) programs. Also, tools like valgrind get you 99% of the benefit of memory safety, which is good enough for debugging. C++ lets you override the allocator, and build in inexpensive (fast enough for production) checks for most use after frees, memory consumption profilers / leak detection/ etc. I’d argue that python is memory unsafe in practice, since we get segfaults from third party dependencies in python about as often as we see them in c/c++. Crucially, C and C++ provide enough tools to get static type safety on the error handling path. Errors like ‘assert “” is not None’ and missing field exceptions in python error handling code are frequent, but unheard of in C/C++. If you use std::string, adding a in integer does something well-defined (rtfm). Adding an int to a char widens the result to the int type (foiling attempts to use it like a char without a downcast, if you use -Wall -Werror). Adding an into to a char* does pointer arithmetic, which can be used safely, but there are better string / buffer types you can implement in an afternoon, so do that instead.

lvh 8y ago
> In fact, C and C++ are both strongly typed, but they are both memory unsafe. You are refuting my point but provide no evidence and implicitly redefine several terms in a way contrary to common usage. Is there a definition you can pen down? Because C sure isn't strongly typed in the Liskov, Jackson or modern usage senses of the term. > Also, tools like valgrind get you 99% of the benefit of memory safety, which is good enough for debugging. C++ lets you override the allocator, and build in inexpensive (fast enough for production) checks for most use after frees, memory consumption profilers / leak detection/ etc. Would you say that de facto C/C++ has a memory safety problem? If it does, why? (Also, not germane to my point.) > I’d argue that python is memory unsafe in practice, since we get segfaults from third party dependencies in python about as often as we see them in c/c++. Do you have extraordinary evidence to go with this extraordinary claim, or are you just talking about your own anecdata? (Also, not germane to my point.) > If you use std::string, adding a in integer does something well-defined (rtfm). My argument was not that it is poorly defined. Weak typing doesn't mean UB.

marcosdumay 8y ago

> I dunno, a wchar_t or something Most likely a char or a * wchar. Yeah, random pointers.