Why I prefer attrs over dataclasses

[@t0prar]

I came here to tell you that you're wrong but you made a really good point when facing customers locked on a specific version of Python. Great video!

[@arisweedler4703]

Just curious, before being convinced what would your argument have been? I can think of one argument: The fact that it is built in to python (and I understand why this is no longer an argument after the video!)

[@fus3n]

if anyone tells me to use old shit I am quitting the job I always stick to new stuff, it's like OCD I can't use old stuff unless new one is likely unstable

[@dhkatz_]

@@fus3n Then you will never get a job anywhere

[@t0prar]

@@arisweedler4703 yes. It mostly comes down to that. So there's no technical reason. On personal projects on smaller teams I don't see any issue with using any alternative. Hiring someone and expecting them to know about how the intricacies of other libraries work that do more or less the same as preexisting ones increases the amount of onboarding time we need to give to each team member. Hiring a Python developer that doesn't know about slots and dataclasses means they might just not be on that level yet. That in addition we have to manage another dependency versioin to sync across teams and that triggers rebuilding your platform for each release. Because of that it doesn't seem to be worth it from my pov.

[@fus3n]

@@dhkatz_ then I will go for my own startup where people aren't idiots and use proper tools (meant other companies BTW)

[@vorpal22]

Nice. I have been using dataclasses since their release and we're working on an internal project (Py3.11 required). I have never actually used attrs myself, but have seen others use it, and you make some good arguments for preferring it.

[@Mekuso8]

My problem with both dataclasses and attrs is that they're not type safe. Similar to your "nmae" typo, if you declare slmething as an int, but put a string there, now you get no errors but incorrect data in your application. Pydantic, on the other hand, solves this perfectly. Pydantic 2.0 was recently released and increases performance significantly. I really like how Pydantic is tightly integrated in frameworks that benefit greatly from type safety, like Litestar.

[@Madinko12]

Pydantic = cancer

[@matthewgamble9934]

By default, Pydantic doesn't validate on assignment. It only on construction.

[@yash1152]

use pylance error reports

[@helboy1111]

Pedantic will try to coerce it into an int and then throw an error if it’s not possible. One could make the argument this is a nice feature or if one’s less familiar with Pydantic a unexpected bug. Further more this case can be handled in all the above libraries by using validation.

[@Mekuso8]

@@helboy1111 Having type safety by default is a massive advantage, just like attrs doing slots by default is an advantage. Having to define validators for everything is error prone.

[@anon_y_mousse]

I just checked and I've only got Python 3.9.4, so using a newer feature would require updating, something I don't generally like doing, especially for scripting languages because of users. Personally, this is one of the key reasons to prefer a compiled language, because you don't have to worry about what version the user has, just provide all the library dependencies or static build and you'll be fine. And I know, you can compile Python into a binary format, but it's not as optimized as it should be, it's some of the laziest translation I've seen for all of the different methods of conversion. I know, not the point of Python as optimization is nearly never a concern, but honestly, I only learned Python so I could translate it to C, and I mean C, not C++.

[@sadhlife]

personally whenever i need to inherit dataclasses or start using some default values, I often hit the ceiling of what's possible with the built in module. the fact that you can't define attributes without defaults after ones with defaults (even if they come from a superclass) is often the deal breaker.

[@PetrSzturc]

Exactly me. Start with dataclass and then leave it on first hurdle. No one wants to read through fields, defaults etc when they are familiar only with __init__.

[@Kaniee96]

I had a similar experience with dataclasses a couple of years ago. But I'm giving it in my latest project another try because I discovered two things: 1. When setting kwargs_only=True you can create child classes with more attributes without defaults. 2. I'm relying more on duck typing now since I discovered Protocols, so I don't lose the powers of typing checking with pyright. What still annoys me is the fact that I can't initialize the fields (where init=True) on an immutable type in the __post_init__ function.

[@atrus3823]

If you could, what you the constructor look like? It's the same reason you can't define a function def my_func(a = 1, b). I have run into how annoying this is when inheriting, but it's the same problem. The new constructor will have the attributes in order from the superclass as arguments, and then the new attributes from the subclass. I don't know enough about attrs to know how it handles this differently, but I'm not sure how you could get around this without mangling the order, which I could see leading to a whole host of problems.

[@sadhlife]

@@atrus3823 attrs does change the order, what problems do you think occur from that? when I use attrs it's almost always a case where I will have to pass everything as a keyword argument anyway to avoid confusion. If there were only 2-3 arguments I'd have used NamedTuple or dataclasses

[@atrus3823]

@@sadhlife If it enforces keyword-only, then I don't see a problem. However, if you set kw_only on dataclasses, it also doesn't have a problem with defining fields with a default before fields without a default. If you didn't ensure keyword-only, then imagine a class A: a: int = 1; b: int. It would have to write the constructor def __init__(b, a = 1): ... Now, you've instantiated this class all over your code (e.g., A(3, 4), i.e., b = 3, a = 4), and someone decides b needs a default value. Now it reverses the constructor args, and every instantiation A(3, 4) now means a = 3 and b = 4.

[@meepisdispenser5651]

honestly i cant believe it took me THIS long to find theres a dataclass library that lets you convert values on the constructor, i really needed that...

[@MarthinusBosman]

The locked on specific python version is a good point, but for personal projects or packages I hope they stick to dataclasses. Just in fear of every repo having a different standard.

[@johnjoyce]

Handwriting or code generation is strong because it guarantees someone can always read the source and not need to know about the dependencies or imports as much. decorators are effectively macros but still come off magical.

[@steinnhauser3599]

amazing! The bumping of the package rather than the python version is really the biggest factor for me

[@user-hk3ej4hk7m]

For simpler things I often use NamedTuple instead of dataclass, it's kind of a deal breaker that they don't work with generics though

[@romsthe]

I started using attrs recently to automate de-serialization and validation, sometimes with custom validators and converters. I don't like the exceptions generated by bad data though, the messages are not great and a bit cryptic for the client user

[@geeshta]

What about Pydantic?

[@danielgysi5729]

I remember when I first started getting serious about Python, and everyone was saying "In Python, there's always one right way to do something and it's usually pretty obvious." You see it repeated all the time in this community but I don't really think it's true. Little rivalries like dataclasses vs attrs exist and then there's the package management problem. Anyway I stopped using python for personal projects and I've been happier I think.

[@k98killer]

What is your replacement language?

[@Graham_Wideman]

Yeah, there are seeming increasing number of ways in which there was no right way to do something to now three possible ways to optionally do something. Resulting in a messy landscape where a codebase might or might use some of these features, and that usage might vary from one class or module to another.

[@danielgysi5729]

@@k98killer Rust mostly. Admittedly the learning curve is much steeper and Python is definitely better as a first language, but the tooling in rust is a breath of fresh air and personally I like that people who write rust care more about performance, since I enjoy optimizing. This is from the perspective of hobby projects though. At work I write Java and PHP.

[@lawrencedoliveiro9104]

Personally, if I’m creating a one-off object, often a dict is just fine. For example, I did a Python wrapper for the Asterisk telephony engine. I looked at other wrappers, and their event-listener calls return a separate event subclass for every event type, with attributes specific to that event type. Me, I didn’t bother, I just return a dict with the appropriate fields in each case. Am I lazy? Yes, I’m lazy. I put my effort into things like the option for SSL/TLS connections, and supporting both sync and async versions of calls, which as far as I can tell, nobody else does.

[@XCanG]

I don't use neither, instead I use Pydantic. I can't tell about slots exactly, may be it is using slots, may be not, but it does everything else that you have and it forcing to use validator at least on typing level and may be more if you need more validations, such as number in range, e.g. "ge=0" (greater equal) or lists with "min_items=1" or strings with "regex=r'whatever' ", they have both defaults and defaults factory, can set optional or required parameters (... - Ellipsis is used if set "defaults=..."), and forget to mention they have same Field() attribute, like "x: list[int] = Field(default=..., title="Can give a name here", description="Can describe here", min_items=1)". Title and description can be used for both IDE showing what this parameter do or autodocs like Swagger. Pydantic used by default in FastAPI, but I also use it outside of FastAPI projects too. And 2 last comments I want to tell: 1) For transmitting model back into front or over the internet it have convenient methods like ".dict()" and more to that it have useful parameters like exclude unset parameters, exclude defaults, exclude none or just exclude from a list of strings. This method return JSON in the end and it does not have issues like as if you do with "json.dumps(my_dict)" when dict has unusual types like datetime, etc. 2) There absolutely no issue with amounts of fields like positional, e.g. "x: int" and keywords like "y: int = Field(...)" and you can have like first keyword, 2nd positional, 3rd keyword, etc. and you wont get error about this. So it is allow for sorting fields in a way you need and no need to use hacks to make it work. It was a really big issue for me before I used Pydantic.

[@johnjoyce]

But as always great, fast concise coverage. You do make wonderful Python videos that are very practical and real and do not focus on the same old stuff covered everywhere else. I hope you produce a book.

[@TheOnlyEpsilonAlpha]

I currently take a deep dive into dataclasses as a python beginner 🤔just begun to write code. And with a outside view from dataclasses vs attr, I will choose on a project basis which one to choose. - When the project is to complicated and restricted in terms of versioning I would use attrs - When it would be implemented in python and I can effortlessly upgrade, then I use dataclasses. I have anyway CI/CD pipelines in place with multiple versions testing for each commit, so if anything breaks on newer versions I can take a look at it

[@nexovec]

I didn't actually use those, I tried to avoid classes because of how much boilerplate there is and how slow the software designs tend to be with them. This makes it significantly more ergonomic. Thanks

[@POINTS2]

The Python versioning is problem that is an issue. On systems with Ubuntu 20.04, it has Python 3.8 which means that scripts will not run with dataclasses with slots=True.

[@loic1665]

thanks for this video! I've actually never used attrs, always dataclasses... But after your video, I will take a look! I'm especially curious about validators and the fact that certain attributes can be frozen, but not all of them. Also slots as default is great

[@osquigene]

Had no idea attr existed, but your arguments seems valid so I might use this in the future. As often, good video :)

[@norude]

Please! Start making videos on rust. Rust can be really confusing sometimes, but you manage to explain every topic you tackle nice and simple

[@DrDeuteron]

bro: get that rusty crap outta here. This is a python space.

[@AZIARGROUS]

@@DrDeuteron he does quite a bit of C++ as well so not really

[@david_lev]

Hi, thanks for the video! Which is the fastest in terms of creating instances?

[@nnii-rn7co]

Thanks for the video! What do you think attrs vs pydantic?

[@Max-mx5yc]

I wish python had macros or anything to make source generation like this easier... I'm pretty fed up with the pseudo-oop and overuse of reflection that writing a python metaprogramming library often requires.

[@CrazyDalekCaan]

I'd really love to see your take on pydantic dataclasses as an alternative to each!

[@loic1665]

I think mCoding already a video where he compared tuples, namedtuples, dataclasses etc... and pydantic!

[@mCoding]

Yep! kzbin.info/www/bejne/rHSvlqeandiqg8k

[@alexandreboisselet8336]

What about the old param library?

[@nevokrien95]

Is usually hand wrote but that frozen thing feels really good

[@rafalemiec8683]

when I first discovered dataclasses three years ago my mind was blown, but I had to implement a few validators took me some time and it worked, but only now you're telling me there's already a tool for it? damn

[@danielwilkowski5899]

The actual thing that makes this code simple, is the abstraction - hiding details in a more high-level solution. The particular solution, like attr or dataclass is not that important.

[@BrianStDenis-pj1tq]

I agree with your presentation, but we chose between dataclasses and pydantic. I would like to hear what you think about dataclass/attrs vs pydantic.

[@mCoding]

Then check out my video where I compare dataclasses, attrs, and pydantic!

[@victorkolis3438]

What do you think about pydantic?

[@maksimon519]

i use strict mode pylance so typo is never a problem. i still think dataclass is better designed. it does not have those over powerful tools that might change what a python code should looks like and behaves, which is good.

[@GRAYgauss]

How about attrs vs pydantic?

[@lawrencedoliveiro9104]

4:42 My clients mainly use Debian Stable on their servers. So I go by whatever Python version is included as standard, e.g. 3.9 for Debian 11, 3.11 for Debian 12.

[@mattlau04]

I also have been using attrs before switching to dataclasses when they got introduced, but i had no idea attrs had all these neat features, i'll probably switch back

[@lawrencedoliveiro9104]

3:50 I encountered this pitfall when defining read/write properties on wrapper classes for the Cairo graphics library. Nowadays I reflexively put ‗‗slots‗‗ on my wrapper classes, just in case.

[@benronen3338]

You're great man! If performance isn't an issue, would you still go with attrs over pydantic?

[@mCoding]

Since pydantic's primary goal is parsing, it has a lot of defaults that are specific to that goal, like eager conversions. Attrs aims to be a more general class building utility library. Although if you look at my dataclass alternatives video, you can see that pydantic performance is not just worse, it's much worse, like 10x worse because of all the validation. In a small script that may not matter, but if you have a whole application, all those 10x perf hits can add up to be an issue even if you don't care much about performance.

[@oida10000]

Interesting I only learned about dataclasses through your old video about them, do you still stand by that video?

[@priteshrana6930]

These are really great tips, thank you.

[@tntmaster3708]

Personally, I write the boilerplate myself. I understand the benefits of dataclasses/attr, but I would rather be sure of my own code. I do agree with many of your points though. Both dataclasses and attr are great tools to reduce boilerplate and write less flaky code. But in my personal experience, I find that I would rather have full control over what I define in any given class. 😅

[@orterves]

I wonder if there could be an ide shortcut to apply the generated code to the source and remove the annotation, for an annotated class? You get to see the code and could modify the class later if necessary, but don't need to do the tedious bit yourself.

[@thisoldproperty]

Loved the instant replay!

[@inkuban]

How is this different than using a TypedDict implementation in a class?

[@davititchanturia]

looks like it needs to compile each time during startup? no caching because of eval ?

[@TN-ec6ec]

No mention of NamedTuple? 😊

[@stonemannerie]

My number one reason why I choose attrs over dataclasses is inheritance from a baseclass with kw arg fields and adding a positional field in the subclass. Just doesn't work in dataclasses. (Atleast py38, but I'm one of the poor guys stuck with it for the foreseeable future, thanks nvidia)

[@Jeyekomon]

Do you always want all this functionality? Like if you use it for your class Employee and later find out that Alice < Bob makes no sense but does not raise any error.

[@mCoding]

No, you wouldn't normally set all the options to True. You would only set the order/compare parameter to True if comparing those elements makes sense. If it doesn't, then set it to False (the default).

[@Jeyekomon]

@@mCoding Ah, I didn't notice that ordering is disabled by default. Sorry, my bad. Thank you for the explanation!

[@JohnMitchellCalif]

super useful! Subscribed

[@BosonCollider]

msgspec is my new favorite library for this usecase

[@geeshta]

I've always used dataclasses or Pydantic depending if I need parsing and validation or not. I never knew attrs and slots by default is neat! For validation I always used Pydantic not sure if there's a difference.

[@doronvaida]

I prefer pydantic because it has all kinds of ultra specific types that can save a lot of validation, so much in fact that i don't use pydantic validator for validation but for mutation when needed

[@Georgehwp]

Should I use pydantic over attrs since the 2.0 update and it's new high performance?

[@mCoding]

I'd say that Pydantic and attrs are for different purposes, I made a whole video about it here kzbin.info/www/bejne/rHSvlqeandiqg8k In short, if you are parsing data that you do not trust, e.g. from a web request, then Pydantic is probably what you want. But if your goal is not parsing and you do trust the data, e.g. because it is generated internally by your application, then Pydantic (even V2) will be orders of magnitude slower than attrs because attrs does not perform any data validation.

[@Georgehwp]

​@@mCoding thanks a lot for getting back to me. Really appreciate it.

[@MrOmsa12]

Does attra support nested attrs objects?

[@knut-olaihelgesen3608]

I have never in my 4 years of using Python ever needed to use dataclasses or attrs. In my projects, there were simply no need for a data structure with complex boilerplate

[@Phaust94]

Never used attrs myself. Using dataclasses all the time, left and right. Python 3.9, using slots auccessfully

[@fantasypvp]

the whole point of attrs writing the code for you I feel like is a negative, since it does this at runtime which seems like it might have a performance cost. I would rather write more verbose code than have all of it done at runtime

[@mCoding]

Keep in mind that attrs (and other dataclass-like alternatives) use a decorator on your class object, meaning they execute once *per class definition*, not once per instance. This means that any performance penalty is small and you will incur it at the very beginning of your program when you import your modules. In the wild though, attrs instances tends to be *faster* and *more efficient* at runtime because attrs will happily do all the little optimizations that a human programmer wouldn't bother with because it takes so much typing and is easy to mess up, like defining slots by default and implementing readonly properties by writing a custom setattr that only runs when an attribute is written to rather than using the much slower @property decorator that runs also when a field is read from.

[@sherpya]

what about pydantic?

[@hasanaljamea2569]

Im looking forward to attrs tutorial

[@kosmonautofficial296]

1:42 it was but I guess I normally do that

[@jeroenvermunt3372]

Personally I am moving to pydantics BaseModel whenever possible. Is there a reason to prefer attrs over pydantic?

[@mCoding]

You may like to see my comparison video between attrs and other dataclass solutions, including pydantic. Pydantic is not recommended for general purpose classes, but it does a great job if you goal is parsing and validating input. kzbin.info/www/bejne/rHSvlqeandiqg8k

[@jeroenvermunt3372]

@@mCoding Thanks! I checked it and it makes a lot of sense

[@brunoais]

IDEs usually help with that part but I get it.

[@Araragi0xff]

I use dataclasses, slots don't seem necessary. If I misspell an attribute it's get caught by mypy or pylint. If I need perfomance I don't use python :)

[@YTCrazytieguy]

What about Pydantic?

[@hugo-onzakorderra8851]

Okay with dataclasses. But why not Pydantic?

[@Gordiigg]

attrs does not support protected attributes, and it is really annoying. From the docs: “attrs follows the doctrine that there is no such thing as a private argument”. This is a very big no for me. But dataclasses do lack many features that attrs have, so it is not a perfect option either. After spending some time with fastapi I’m thinking about using pydantic instead of attrs and dataclasses for some of my projects. On the paper, it has all the features that I need, so I’m hoping for the best!

[@ArturJD96]

Just before you said to watch again this beautiful refactor I stopped your video and rewinded myself. ROTFL when you did exactly the same soon after yourself.

[@bigmacbeta]

Thank you. Thank you. Thank you.

[@Scymet]

I use attrs too !

[@TheMegaMrMe]

I just switched to Typescript

[@krzysztofjarek6476]

0:36 Hey James, "who can even remember all of them?" - a class with 3 atrributes would not be memorable? ;)

[@mentisdominus]

🙂 James was talking about remembering all the boilerplate functions that would need to be implemented.

[@krzysztofjarek6476]

@@mentisdominus It was just a joke. I wanted him to respond to this provocation ;)

[@whamer100]

well well well, i have a new toy to play with now, dont I 👀

[@angelcaru]

Disagreed. +1 3rd-party dependency == +1 moving part.

[@rx97_mc]

the update to `@define` and modern attrs is really attractive and I do agree with many of your points. one thing i've seen though is that `mypyc` (a compiler that is bundled with `mypy`) isn't able to compile attrs classes to a more optimized struct-like thing as it can w/ `dataclasses`.

[@UltravioletMind]

I use dataclasses but i'll give attrs a shot tonight

[@jullien191]

Hei fra Norge!

[@Ca1vema]

"In the world where many companies still use python 3.8" TFW your company still uses python2.7 😢

[@mai6666]

pydantic is also good

[@doresearchstopwhining]

Pydantic all day ftw....

[@zackadam2598]

What I think: I stopped trying to do OOP in python and use Rust’s far superior type system instead (generics, traits, enums, etc). Believe it or not, it’s actually much simpler to understand than all these python decorators in classes.

[@shadowviper95]

Out of curiosity, what do you use as your “struct” equivalent if not data classes? I often do the same with rust style syntax, but reach for data classes to maybe a named triple if it’s immutable for my “struct and or impl group”

[@PetrSzturc]

Could you provide small example py class vs rust? I am interested in Rust but haven't fully tried it yet.

[@lawrencedoliveiro9104]

Python has metaclasses, though.

[@prorok_postmoderny]

Pydantic

[@driden1987]

Looks like someone ported Lombok over to python heh

[@freeseacher]

why not use pydantic ?

[@mCoding]

I made a whole video to answer this question :) kzbin.info/www/bejne/rHSvlqeandiqg8k

[@rx97_mc]

@@mCoding might be slightly outdated since pydantic v2 is a pretty large rework of the library, esp considering performance

[@trag1czny]

discord gang 🤙🤙

[@amir3515]

is slow

[@adamcetinkent]

It's mad to me that you pronounce "attrs" as "adders"

[@unflexian]

If you don't define your classes by manually writing cpython bytecode and assembling it at runtime with marshal or xasm you aren't a real python programmer...

[@hectord4693]

😳 promo sm

[@reimusklinsman5876]

I don't use attrs or dataclasses. I've never really found either of them particularly useful and really hate when stuff is working under the hood. It just adds too much trivia to a project. Also, I absolutely loathe pythons syntaxes for defining a variable type. It adds so much clutter and doesn't do anything.

[@mCoding]

Fun fact! Although I showed lots of type annotations in this video, attrs is fully compatible with using zero type annotations.

[@ЕвгенийКрасилов-о9о]

Seems like rust suits you more than python 😅

[@michaelscott6214]

I use vim btw

[@Graham_Wideman]

Why are you telling us?

[@gkett19]

barf

[@sulfur32066]

pydantic...

[@adobko]

Pydantic is better in my opinion

[@mCoding]

Check out my video comparing pydantic as well!

[@jedpittman6739]

“post the wrong code to stack overflow and wait for someone else to write it for you” 😂😂😂

[@nickeldan]

pydantic is my to go.

[@andrewking7958]

Hi! What about "Msgspec"?