this post was submitted on 14 May 2024
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Python is great, but stuff like this just drives me up the wall (lemmy.world)
submitted 7 months ago* (last edited 7 months ago) by renzev to c/[email protected]
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Explanation: Python is a programming language. Numpy is a library for python that makes it possible to run large computations much faster than in native python. In order to make that possible, it needs to keep its own set of data types that are different from python's native datatypes, which means you now have two different bool types and two different sets of True and False. Lovely.

Mypy is a type checker for python (python supports static typing, but doesn't actually enforce it). Mypy treats numpy's bool_ and python's native bool as incompatible types, leading to the asinine error message above. Mypy is "technically" correct, since they are two completely different classes. But in practice, there is little functional difference between bool and bool_. So you have to do dumb workarounds like declaring every bool values as bool | np.bool_ or casting bool_ down to bool. Ugh. Both numpy and mypy declared this issue a WONTFIX. Lovely.

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[–] [email protected] 107 points 7 months ago* (last edited 7 months ago) (1 children)

bool_ via Numpy is its own object, and it's fundamentally different from bool in Python (which is itself a subclass of int, whereas bool_ is not).

They are used similarly, but they're similar in the same way a fork and a spork can both be used to eat spaghetti.

[–] Donkter 66 points 7 months ago (2 children)

And do you eat that spaghetti out of a bool?

[–] [email protected] 3 points 7 months ago* (last edited 7 months ago)

Class SpaghettiBool:

def contain_spaghetti():
    pass

sure, why not.

(I'm too lazy to do a proper Protocol)

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[–] [email protected] 86 points 7 months ago* (last edited 7 months ago) (2 children)

Honestly, after having served on a Very Large Project with Mypy everywhere, I can categorically say that I hate it. Types are great, type checking is great, but applying it to a language designed without types in mind is a recipe for pain.

[–] [email protected] 17 points 7 months ago

Adding types on an untyped project is hell. Greenfield stuff is usually pretty smooth sailing as far as I’m concerned…

[–] [email protected] 13 points 7 months ago (1 children)

In my experience, mypy + pydantic is a recipe for success, especially for large python projects

[–] scrion 7 points 7 months ago (1 children)

I wholeheartedly agree. The ability to describe (in code) and validate all data, from config files to each and every message being exchanged is invaluable.

I'm actively looking for alternatives in other languages now.

[–] [email protected] 9 points 7 months ago (2 children)

You're just describing parsing in statically-typed languages, to be honest. Adding all of this stuff to Python is just (poorly) reinventing the wheel.

Python's a great language for writing small scripts (one of my favorite for the task, in fact), but it's not really suitable for serious, large scale production usage.

[–] scrion 2 points 7 months ago (1 children)

I'm not talking about type checking, I'm talking about data validation using pydantic. I just consider mypy / pyright etc. another linting step, that's not even remotely interesting.

In an environment where a lot of data is being exchanged by various sources, it really has become quite valuable. Give it a try if you haven't.

[–] [email protected] 4 points 7 months ago (1 children)

I understand what you're saying—I'm saying that data validation is precisely the purpose of parsers (or deserialization) in statically-typed languages. Type-checking is data validation, and parsing is the process of turning untyped, unvalidated data into typed, validated data. And, what's more, is that you can often get this functionality for free without having to write any code other than your type (if the validation is simple enough, anyway). Pydantic exists to solve a problem of Python's own making and to reproduce what's standard in statically-typed languages.

In the case of config files, it's even possible to do this at compile time, depending on the language. Or in other words, you can statically guarantee that a config file exists at a particular location and deserialize it/validate it into a native data structure all without ever running your actual program. At my day job, all of our app's configuration lives in Dhall files which get imported and validated into our codebase as a compile-time step, meaning that misconfiguration is a compiler error.

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[–] renzev 2 points 7 months ago

Gradual typing isn't reinventing the wheel, it's a new paradigm. Statically typed code is easier to write and harder to debug. Dynamically typed code is harder to debug, but easier to write. With gradual typing, the idea is that you can first write dynamic code (easier to write), and then -- wait for it -- GRADUALLY turn it into static code by adding type hints (easier to debug). It separates the typing away from the writing, meaning that the programmer doesn't have to multitask as much. If you know what you're doing, mypy really does let you eat your cake and keep it too.

[–] someacnt_ 82 points 7 months ago (3 children)

What years of dynamic typing brainrot does to mf

[–] [email protected] 18 points 7 months ago (1 children)

I currently work on a NodeJS/React project and apparently I'm going to have to start pasting "'any' is not an acceptable return or parameter type" into every damned PR because half the crazy kids who started programming in JavaScript don't seem to get it.

For fucks sake, we have TypeScript for a reason. Use it!

[–] [email protected] 15 points 7 months ago (1 children)

if you have a pipeline running eslint on all your PRs (which you should have!), you can set no-explicit-any as an error in your eslint config so it's impossible to merge code with any in it

[–] FunkFactory 4 points 7 months ago

+1 if you can have automated checks do part of your reviews for you, it's a win. I never comment about code style anymore, if I care enough I'll build it into the lint config

[–] [email protected] 5 points 7 months ago

I learned Python as my first programming language, but ever since I got into other languages, I don't like going back to dynamic typing...

[–] ZILtoid1991 5 points 7 months ago

That's actually a quite bad way of naming types, even if someone really insists on using 32 bit integers for bools for "performance" reasons.

[–] [email protected] 67 points 7 months ago (1 children)

Type checker detecting different types?

surprisedpikachu.png

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[–] [email protected] 41 points 7 months ago* (last edited 7 months ago) (1 children)

Data typing is important. If two types do not have the same in-memory representation but you treat them like they do, you're inviting a lot of potential bugs and security vulnerabilities to save a few characters.

ETA: The WONTFIX is absolutely the correct response here. This would allow devs to shoot themselves in the foot for no real gain, eliminating the benefit of things like mypy. Type safety is your friend and will keep you from making simple mistakes.

[–] [email protected] 13 points 7 months ago (2 children)

Even if they do have the same in-memory representation, you may want to assert types as different just by name.

AccountID: u64

TransactionID: u64

have the same in-memory representation, but are not interchangeable.

[–] [email protected] 7 points 7 months ago

That is a very solid point. If user-defined types are NOT explicitly defined as compatible (supposing language support), they should not be.

In your example, if it were, say a banking system, allowing both types to be considered equivalent is just asking for customer data leaks.

[–] [email protected] 2 points 7 months ago

Python does allow this with NewType. Type checkers see two different types, but it is the same class at runtime.

[–] [email protected] 39 points 7 months ago (1 children)

Well yeah just because they kinda mean the same thing it doesn't mean that they are the same. I can wholly understand why they won't "fix" your inconvenience.

[–] [email protected] 8 points 7 months ago (1 children)

Unless I'm missing something big here, saying they "kinda mean the same thing" is a hell of an understatement.

[–] [email protected] 13 points 7 months ago (2 children)

They are two different data types with potentially different in-memory representations.

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[–] eager_eagle 31 points 7 months ago* (last edited 7 months ago) (10 children)

So you have to do dumb workarounds like declaring every bool values as bool | np.bool_ or casting bool_ down to bool.

these dumb workarounds prevent you from shooting yourself on the foot and not allowing JS-level shit like "1" + 2 === "12"

[–] semperverus 2 points 7 months ago* (last edited 7 months ago) (2 children)

The JS thing makes perfect sense though,

"1" is a string. You declared its type by using quotes. myString = "1" in a dynamically typed language is identical to writing string myString = "1" in a statically typed language. You declare it in the symbols used to write it instead of having to manually write out string every single time.

2 is an integer. You know this because you used neither quotes nor a decimal place surrounding it. This is also explicit.

"1" + 2, if your interpreter is working correctly, should do the following

  • identify the operands from left to right, including their types.

  • note that the very first operand in the list is a string type as you explicitly declared it as such by putting it in quotes.

  • cast the following operands to string if they are not already.

  • use the string addition method to add operands together (in this case, this means concatenation).

In the example you provided, "1" + 2 is equivalent to "1" + "2", but you're making the interpreter do more work.

QED: "1" + 2 should, in fact, === "12", and your lack of ability to handle a language where you declare types by symbols rather than spending extra effort writing the type out as a full english word is your own shortcoming. Learn to declare and handle types in dynamic languages better, don't blame your own misgivings on the language.

Signed, a software engineer.

[–] lwuy9v5 11 points 7 months ago

TypeError is also a correct response, though, and I think many folks would say makes more sense. Is an unnecessary footgun

[–] eager_eagle 2 points 7 months ago* (last edited 7 months ago) (1 children)

of course it makes sense, the language has made questionable choices that make working with it a frustrating experience - and that's by design

A reasonable language would raise/return an error because a wrong result is often more harmful than an error.

Signed, a software engineer.

lol

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[–] RustyNova 28 points 7 months ago (2 children)

Good meme, bad reasoning. Things like that are why JavaScript is hated. While it looks the same, It should never, and in ANY case be IMPLICITLY turned into another type.

[–] [email protected] 4 points 7 months ago

Typing and function call syntax limitations are exactly why I hate JS.

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[–] breadsmasher 18 points 7 months ago* (last edited 7 months ago) (6 children)

This explanation is pretty clear cut

What exactly is your use case for treating np.bool_ and bool as interchangeable? If np.bool_ isn't a subclass of bool according to Python itself, then allowing one to be used where the other is expected just seems like it would prevent mypy from noticing bugs that might arise from code that expects a bool but gets an np.bool_ (or vice versa), and can only handle one of those correctly.

mpy and numpy are opensource. You could always implement the fix you need yourself ?

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[–] [email protected] 11 points 7 months ago (4 children)

So many people here explaining why Python works that way, but what's the reason for numpy to introduce its own boolean? Is the Python boolean somehow insufficient?

[–] [email protected] 21 points 7 months ago

From numpy's docs:

The bool_ data type is very similar to the Python bool but does not inherit from it because Python’s bool does not allow itself to be inherited from, and on the C-level the size of the actual bool data is not the same as a Python Boolean scalar.

and likewise:

The int_ type does not inherit from the int built-in under Python 3, because type int is no longer a fixed-width integer type.

[–] breadsmasher 8 points 7 months ago* (last edited 7 months ago)

here’s a good question answer on this topic

https://stackoverflow.com/questions/18922407/boolean-and-type-checking-in-python-vs-numpy

plus this is kinda the tools doing their jobs.

bool_ exists for whatever reason. its not a bool but functionally equivalent.

the static type checker mpy, correctly, states bool_ and bool aren’t compatible. in the same way other type different types aren’t compatible

[–] [email protected] 6 points 7 months ago (2 children)

Technically the Python bool is fine, but it's part of what makes numpy special. Under the hood numpy uses c type data structures, (can look into cython if you want to learn more).

It's part of where the speed comes from for numpy, these more optimized c structures, this means if you want to compare things (say an array of booleans to find if any are false) you either need to slow back down and mix back in Python's frameworks, or as numpy did, keep everything cython, make your own data type, and keep on trucking knowing everything is compatible.

There's probably more reasons, but that's the main one I see. If they depend on any specific logic (say treating it as an actual boolean and not letting you adding two True values together and getting an int like you do in base Python) then having their own also ensures that logic.

[–] [email protected] 2 points 7 months ago

You know, at some point in my career I thought, it was kind of silly that so many programming languages optimize speed so much.

But I guess, that's what you get for not doing it. People having to leave your ecosystem behind and spreading across Numpy/Polars, Cython, plain C/Rust and probably others. 🫠

[–] [email protected] 2 points 7 months ago

This is the only actual explanation I've found for why numpy leverages its own implementation of what is in most languages a primitive data type, or a derivative of an integer.

[–] [email protected] 5 points 7 months ago* (last edited 7 months ago)

Someone else points out that Python's native bool is a subtype of int, so adding a bool to an int (or performing other mixed operations) is not an error, which might then go on to cause a hard-to-catch semantic/mathematical error.

I am assuming that trying to add a NumPy bool_ to an int causes a compilation error at best and a run-time warning, or traceable program crash at worst.

[–] [email protected] 2 points 7 months ago* (last edited 7 months ago) (2 children)

I mean, naming something bool_ should be the first red flag. Python and its ecosystem is a shit show.

[–] AdamEatsAss 4 points 7 months ago

Python is an interpreted language. You can interpret my nuts, get wrecked. Python gang for lyfe.

[–] breadsmasher 4 points 7 months ago (1 children)

Numpy named it bool_ not base python

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