This Is Why Python Data Classes Are Awesome

Data classes in Python are really powerful and not just for representing structured data. In this video, I show you what you can do with dataclasses as well as new capabilities that have been added in Python 3.10.
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👀 Code reviewers:
- Yoriz
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- Dale Hagglund
🎥 Video edited by Mark Bacskai: / bacskaimark
🔖 Chapters:
0:00 Intro
0:49 What are data classes?
1:37 Explaining the example
4:00 Dataclasses basics
5:45 Assigning default values
8:54 Excluding arguments from the initializer
9:44 Using post_init to generate extra fields
11:25 Private/protected members
11:59 Excluding information from the repr
12:43 Freezing a dataclass
14:59 (new in Python 3.10) kw_only
16:10 (new in Python 3.10) match_args
17:00 (new in Python 3.10) slots
21:30 Final thoughts
#arjancodes #softwaredesign #python
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[@ArjanCodes]

💡 Get the FREE 7-step guide to help you consistently design great software: arjancodes.com/designguide.

[@saketh_s]

One thing to note, when you pass data class "frozen=True", instance is immutable. So at 13:29 you are actually getting error for search_string which we are trying to change at _post_int_ at object creating not for person name (line 25) You can not change fields even inside the class even with setter methods.

[@songsft.googleassistant2542]

May you have tons of subs Arjan cause you're one of the few youtubers whose python codes aren't messed up and you're instructions are on the point and useful.

[@coupmd]

Enjoyed this video. Would enjoy more videos on intermediate/advanced python standard library tools and their examples of their intended use cases.

[@wbellmangmail]

Just came across you channel. I've watched a couple of your other videos as well... I happen to be working on a project and your videos on dependency injection vs. dependency inversion as well as your video on structural pattern matching have been super helpful! Awesome stuff! Thanks for getting content out there (and chapter-izing your videos. ;) )!

[@sbeau]

Arjan, your ability to explain detail in a structured, easy to follow format is second to none. Thank you for another great tutorial.

[@VladimirSanchez]

He's in the same league as Nana! ;)

[@FrankenLab]

@ArjanCodes, great video. I consider myself a casual programmer and have been programming with Python for about 5yrs and absolutely love it. I started programming "casually" in the 80's with C, Pascal, Assembler, then Perl and now Python. I really enjoyed C and Perl, but Python is by far my favorite now. This is the first video I've seen of yours and based on that I just subscribed to your channel. I enjoy your style and explanations and I don't have to play the video at twice the speed waiting for you to get to the point. I'm looking forward to seeing more of your Python videos.

[@bryan_hiebert]

Just like every video from you my knowledge of programming with python is advanced. I really appreciate the content you provide, thank you!

[@Cookie-mv2hg]

Since we're talking a lot about dataclasses, I wonder would it be great combining with sql database. If we could get a review that would be very helpful!

[@vedambala]

Arjan, You should seriously consider doing a full fledged Python course from beginner to advance level laden with Projects so we can learn Python the Pythonic way.

[@aminramazanifar9743]

The final note about slot was really great. Thanks

[@jordansilke3629]

This is truly an excellent successor to your earlier video on data classes, bravo!

[@ArjanCodes]

Thanks Jordan, glad you liked it!

[@barrykruyssen]

Hi Arjan. Great video, very well presented. I've just found your channel and will be watching all your videos as time permits. I'm a retired software engineer (started back in the early 80's). 5 weeks ago I decided, in my retirement, to switch back to linux (and python - which I have never used), just for fun, after 25 years in microsoft products (prior to that I was in the Unix world). I'll be changing 2 of my classes to data classes ASAP. I have just read your Software Design Guide and agree with much of what you've written. I think you have glossed over the most important aspect "Who’s it intended for?". Determining who is doing what, why they do it and what they expect from it and then managing the expectations is the key to a successful implementation. You do mention your “zoom out and zoom in” approach which probably encompasses this but in my planning, the people are the key and if there are problems in this area it can be very costly down the track (we qualified our prospective clients and if the people problem was too great we walked away from deals), as you say we write the code for the client, not for us. Thanks

[@hematogen50g]

I came to Python from C# so I picked up coding quickly. But thinking in python way is harder, so such videos really help me develop python mindset.

[@christensencode7538]

Your videos on dataclasses are awesome! I've used them for a few projects and they really help.

[@robboerman9378]

I love your concise and clear explanations. Going to look into your course!

[@neoporcupine]

Working my way through my third LinkedIn Learning (LIL) Python course, all of which claim to teach you the data structures available. Arjan's short video explains a dozen reasons why you want to use dataclass that the LIL courses didn't include. Thank you!

[@ChrisPatti]

I really love this video! It’s an excellent quick, guided tours to how powerful data classes, can be. Thanks for making it!

[@ArjanCodes]

Thank you Christopher. Glad it was helpful!

[@flynnowen2478]

Love your content Arjan! I've been making an effort to apply your teachings as much as possible in my code. Would you consider doing any future videos on unit testing? I think it would be super useful. I personally use pytest, but you might know better frameworks.

[@paulorsbrito]

What happened to “explicit is better than implicit” and to “there should be only one obvious way to do something”?

[@alfonsov3190]

I had a couple of questions during the video, but immediately after they surged, you addressed them. Thanks a lot, as usual!

[@ArjanCodes]

You're welcome :).

[@amosmunezero9958]

Great tutorial in Python, its been a while I havent done some Python, I didnt know much about DataClass. So thank you.

[@mauisam1]

Again Arjan, another fantastic video. If I become half the programmer you are I will be lucky. But I just have the love of programming so I will continue to work on improving my knowledge and skill set. So many programmer say just read the Docs, but I learn from examples and the Docs usually have few if not poor examples. So a big part of my improvement will be in thanks to your love of sharing your knowledge. Thank you...

[@WalterBoring]

Cool video. I didn't even know about the dataclasses lib until this. I'm putting it into my project now.

[@sambeard4428]

Geweldig en duidelijk overzicht van deze erg handige feature. Gisteren liep ik precies nog tegen deze use case aan, veel boillerplate code. Dit lost het mooi op. Thanks!

[@Volcan-kf3oz]

This guy really know what he is doing every video I've seen he able to break it down to where even a person new to python can understand "if you can't explain it simply, you don't understand it well enough." - Albert Einstein

[@ArjanCodes]

Thank you so much!

[@auroraRealms]

Although I like the ability to learn and use Data Classes. All my years of database programming has taught me to use JSON, and Dictionaries as much as possible. Especially in Web Services. The caveat to using Data Classes is that; changing a column type, name or description, or adding or removing columns ends up as a use case/feature ticket for the programmer which can take a bit of time to run through the development cycle. These column changes are guaranteed to happen all the time, in the life cycle of the product. A second problem, is that the code must be completely thrown out, when starting a new product. Using Dictionaries very often can allow these column changes from config files without recompiling or restructuring the code base. Going back to Web Services. Dictionaries can be web requests and responses, in JSON, without translation. This makes for high performance, and easy maintenance in the life cycle of product. It also makes copying and pasting the code directly into other products a possibility.

[@duaneatnofroth]

I checked out your channel in hopes to see some examples of the techniques you mentioned in your reply above. I think you might get a good response if you ever decide to do some programming videos. I'd love to see some from you.

[@fabio.1]

👀

[@GanklThat]

​​@@duaneatnofrothhe doesn't need to give examples when what he's stating is already best practice when working with data

[@simonetheditch809]

Love the way you teach. Would be so much appreciated if you can make a similar course in C++

[@matthewnuzzaco2849]

This was super helpful, I used some of these tips almost immediately.

[@nyghl]

It was fun to follow along and learn! Thank you ArjanCodes.

[@ninadloke785]

Watching your video for first time. Deserves subscribe!! Great work and thanks!!

[@SystemSigma_]

Nice overview of dataclasses.. Next, we need an extensive video about the testing frameworks and mocking for TDD!

[@techassets]

I have an observation. Even if you remove the person.name = "Arjan" and set the dataclass frozen=True you will have a FrozenInstanceError. Because you use the __post_init__ method and the frozen dataclass does NOT allow it ! So you must remove the __post_init__ method if you want to freeze the dataclass and prove that you cannot modify it after initialization. THANK YOU FOR YOUR AMAZING VIDEOS !

[@MiguelRozsas]

so, you are saying we not have both ? A frozen class and __post_init__ ? There is any workaround for this ?

[@justinpeter5752]

Very good video. I think I learned a lot about classes in this video and I can see where I can use some of these in my code. Well I’m not quite there yet with building classes with multiple inheritance to worry about the issue with slots. But at least I’ll start using slots for performance improvements. Overall, bravo. I’m starting to understand more about Python from a systematical perspective.

[@jma42]

I also want to add that you can actually use asdict method from dataclasses and from_dict method from dacite library. It works as it sounds to be and even works in nested dicts/dataclasses!

[@seans9168]

Great overview and useful examples! Thanks for the video.

[@mampiisaotaku]

i just discovered your channel a few videos back. and what you share is pure gold

[@ArjanCodes]

Thank you so much, glad you like it!

[@qrubmeeaz]

... aaand he's done it again!! Brilliant! Thank you.

[@andywilson1162]

Great work Arjan, I would love to hear how you use the class when dealing with lots of data, do you use a dictionary of that class for example? Is that the best way, etc.

[@christopheanfry2425]

Thank you so much for this video and for the design guide I’ve just download, it’s literally gold 🙏

[@ArjanCodes]

You’re welcome! Glad you find it helpful.

[@AndreyPutilov]

Great explanations! Thanks for the content!

[@equu497]

I wasn't even trying to learn about dataclasses...but it came up on my recommended and I watched the entire thing- Got me thinking I should clean up some old code.

[@NdamuleloNemakh]

Exactly what I've been thinking all along, "strict mode" is a feature that must be seriously considered

[@JoshSmeda]

I really love your videos on these subjects - keep it up!

[@ArjanCodes]

Glad to hear, Joshua - and I will ;).

[@ShahriyarRzayev]

Awesome material as usual, keep going and thanks for sharing)

[@nusermane1076]

Incredibly good explanation, will try this for myself tomorrow 👍👍👍

[@Rebeljah]

I am 100% gonna use the repr=False option, thank you!

[@mattcauth]

Very, very useful and well done. Thank you!

[@JPy90]

Awesome man.! Just arrive to your channel. Seems amazing

[@mpotane]

Wow, the most complete tutorial I've seen. Not a single detail has been missed.

[@ArjanCodes]

Thanks, glad you liked it!

[@zuydra]

Hi Arjan, your videos on Python are the best I have ever seen on KZbin. Please keep up the good work 👍

[@ArjanCodes]

Thanks so much! And will do 😊

[@aungkyawkyaw9114]

next level! Thanks Uncle Arjan.

[@JohnnysaidWhat]

Great video really interesting topic had no idea the data class decorator existed. Just a small suggestion. The top end eq on your voice is a little shrill. DeEsser or small eq to lower the high freq bands. Thank you for this video all the same!

[@Rebeljah]

New AC video! I am actually using DCs right now to define a common set of data for server/client communication. It's very nice because I can subclass a super dataclass in order to get functionality like serialization/deserialization fairly easily. Adding new data types just takes a few lines of code now!

[@centar1595]

So you're enjoying the AC/DC video? :)

[@Rebeljah]

@@centar1595 yes I am! Lol

[@AbhishekVaid]

The progression of introducing features and clarity of explanation is very high ! Great Job !

[@ArjanCodes]

Glad you liked the video!

[@fuadpalchayev7269]

Thank you Arjan!👍

[@fvbakel]

Great overview of the dataclass. I wonder what your view is on binding the dataclass to a SQL database. Is there an easy way? It seems that the Django and sqlalchemy methods are not compatible with the dataclass? Further more, what do you think about nested dataclass and the impact on hashing?

[@Saidffff]

Nice one Arjan! Also, __slots__ give faster attribute access AND space savings in memory due to switching to a more compact data structure. When you create many instances of the class, that is another advantage. Got that from reading 'Python distilled', written by the venerable David M. Beazly.

[@chswin]

Lol a python dev worried about memory allocations…

[@hisamsowaib956]

Hope you can create a video on how we can use dataclasses with data coming from db. I think that is a more real life scenario. Thanks a lot.

[@wv1138]

Good point about a possible strict mode

[@franferri]

Very nice videos Arjan, I have improved my skills a lot with some of the info. May I ask you the brand of the glasses you are wearing? do you have the model.

[@f4bglv]

Excellent video, very informative, concise and enjoyable... as always! Thanks again.

[@ArjanCodes]

Thanks so much Fabio, glad the content is helpful!

[@marknielsen4494]

Super high quality content - thank you Arjan!!!

[@ArjanCodes]

Glad you enjoyed it, Mark!

[@marcioneto3016]

Amazing video, as usual. Here's a suggestion: how about a video on the infamous Visitor pattern next? Thanks for the amazing content. I really liked the Software Designer Mindset course, by the way.

[@ArjanCodes]

Thanks for the suggestion, Márcio, and glad to hear you enjoyed the course!

[@ritzg98]

This guy is excellent. I've only watched a couple of his videos so far. Planning on watching a few more today. Clear, concise, accessible. So far, great!

[@ArjanCodes]

Glad you like them!

[@davidlakomski3919]

I've tried 2 days ago to make a package to manage state of jobs with Pydantic, and even if it was less messy than what I did before, I realize now how easier and cleaner it would have been with dataclasses ! Thanks for the excellent content !

[@ArjanCodes]

Glad it was helpful, David!

[@hcubill]

Love the video Arjan. It's great you explain the new features in 3.10. in my team we wonder what the benefit of upgrading is and this helps a lot!

[@Bushade]

Great video Arjan! Learned quite some new things even though I regularly use dataclasses. One suggestion which I encounter quite often in data science: Where and when to properly calculate additional properties (features for my models) after first initialization when there are dependencies between multiple objects, e.g, you have to wait for both to finish initialization, then calculate features. I'm currently working with a hirarchy of dataclasses and calculate these properties in the top level in __post_init__ but am unsure if that's the best way. Thanks!

[@ArjanCodes]

Thanks so much, glad it was helpful!

[@rrestituti]

Amazing video. I didn't know dataclasses and I found it amazing. Thanks, Arjan . Got a new subscriber.

[@ArjanCodes]

We're glad to have you, welcome aboard!

[@XCanG]

I use similar thing when working with fastapi, library named SQLModel, what it basicaly is very similar to dataclass, but it has validation from pydantic, so if you, say assign to person with a name type int, like Person(name=1), then you get ValidationError exception. It is more useful in fastapi as it may be used as a mechanism to prevent API being called and executed if provided arguments are not match. And you can have more validation methods in Field, like: le, ge, lt, gt; for list types you may provide min/max range, for strings you may add regex or even something more custom via function. I like it a bit more than just dataclass

[@AngelHdzMultimedia]

Great video on Dataclasses! Thank you! Sadly, I had to learn with the docs, then this video popped up... :) +1 for the usage of type annotations. ;)

[@ArjanCodes]

Thanks so much, glad the content is helpful!

[@anthonvanderneut]

13:31 Would it not be more useful to freeze the dataclass after calling __post_init__ , so that it errors on assigning "Arjan" instead of setting the (internal attribute) _search_string?

[@amadzarak7746]

Wow! How did I JUST find this channel. You are awesome man!

[@ArjanCodes]

Welcome aboard! :)

[@naderbazyari2]

I am modifying my code in pycharm right now according to your tips. Awesome video. Much much appreciated.

[@ArjanCodes]

Nice work!

[@wtfKwaku]

OMG, I been working on this project and for like 3 days I been trying assign a class and return something! Great Video!

[@ArjanCodes]

Glad it was helpful!

[@emory_blame]

Hey. Nice video) Everything were fine and helpful until the 21:00 where you suggest to not using the inherent. For newcomers to python I can suggest video called super - is super. It were very helpful to me.

[@Andremzsptm]

Excellent video as always @ArjanCodes!

[@ArjanCodes]

Thanks Andre, glad you liked it!

[@borisvujicic7817]

This is great. ArjanCodes, have you thought about doing a video about Python descriptors? I think it could be very useful, as there is no good ones on KZbin.

[@johntamplin]

Take a look at the videos by Corey Schaffer. A very different style, but equally good, in my opinion. I believe he did one on Python descriptors.

[@metensis]

Great video! You may want to add in a new video the new feature of 3.10 to allow children dataclasses with kw_only

[@alejandropereira5680]

Very useful explanation, to the point and with real use case, really liking these vids

[@ArjanCodes]

Thanks so much Alejandro, glad you liked it!

[@zakseipel9494]

Talking about strict mode that was one of the reasons I started using Black and setting it to a very strict set of rules. It forces me to write leaner code and not be lazy. Comes at a price of extra dev time but worth it.

[@jaa928]

Thank you for the clear and concise explanation. As an experienced programmer, but newcomer to python this was an excellent, example-driven discussion.

[@ArjanCodes]

Happy you enjoyed the content!

[@davecobb5649]

Great video, very helpful. What editor are you using? Thanks

[@rablaze]

Love the videos! I was watching a rerun of a Supernatural episode while watching this and the actor that plays Crowley and you kinda like alike lol

[@ArjanCodes]

LOL, I see what you mean :).

[@thomasoa]

The error you got one the frozen case was not when you set .name = “Foo”, but in the __post_init__ method, setting _query_string. Is there any way to do post_init when using a frozen dataclass?

[@yakkayakka360]

I noticed that too. Glad I'm not the only one. Did you ever get an answer?

[@joxa6119]

Hi Arjan. This is a very excellent video. By the way, can I know what is the extension you used when you run the code (I mean when you click the | > button)

[@dmytroparfeniuk2670]

A question about integration tests. What are you doing with the database when you write your tests? Create a mock of the database or use the same database as on the production but running locally (we also have to to adjust the CI to with the external database somewhere), or run create test connection with sqlite that will be used for testing (also simplify the previous approach but only if you don't use any Postgres-specific stuff in your application)?

[@presstv]

great video. Thanks Arjan

[@shotihoch]

And again... VERY interesting. Started as video for tea-brake, finished in my obsidian, writing down some very interesting tips. Thanks.

[@ArjanCodes]

I'm glad you found the video useful! :)

[@abdelkadergnichi6643]

You are awesome man i really appreciate you work bro your videos are so clear and beefy ❤❤

[@ArjanCodes]

Thank you so much! ❤

[@xl0xl0xl0]

Thank you for the video. You could use the Jupyter integration with vscode to avoid switching back and for the between code and output.

[@ArjanCodes]

Thanks for the suggestion - will look into this!

[@richardmonteiro8694]

so slots =True is just when retreiving infor for computational pov?, and an amazing video once again!

[@Elian_Amselem]

what a nice theme, what's it called? i use python and never hear about dataclasses, very well explained! :)

[@solvability2782]

very cool. I will check it out.

[@radomirmijovic2605]

Great video! Thanks

[@Nieosoba]

thanks, although I usually use dataclasses for validation or/and making specialized operation on large objects when we only need to get piece of that object

[@EW-mb1ih]

Thank you for your video! Is it possible to freeze only some variables and not all variables of the dataclass?

[@bmd203]

When you're talking about freezing the class, unless I'm misunderstanding the error at 13:27, appears to not be your intended restriction. It's not saying that you cannot update the name, it is unable to update your _search_string variable inside the __post_init__ function?

[@yiyangzhang608]

very practical and useful, help me a lot, thank you🍗

[@NeumsFor9]

Do you do a video on the impact of slots on bulk data engineering?