“I’d like to thank me for sponsoring myself” 🤣🤣🤣🤣🤣

It's not just the memory savings. Restricting the ability to add new members is a feature itself. If I make a typo when assigning to an attribute, I want to get an error. I don't want it to be silently ignored, leaving me wondering why the value doesn't change. That is really the main reason I always use slots. Memory savings are just a nice side-effect.

The way you pick examples is phenomenally efficient at highlighting limitations and advantages of whatever functionality you present.

Finally, a great primer on slots!

5:51 "We need to enter the matrix" Wouldn't this be more like leaving the matrix because you're peeking behind the curtain?

“I’d like to thank me, for sponsoring myself.”

The reason to include __dict__ in __slots__ is because it makes it much easier to extend/modify the code, while _still_ giving you memory savings over the default. Anything stored in the __dict__ incurs additional storage overhead not just because of the dictionary headers, but also for (a) storing the _key_, and (b) due to the additional empty nodes needed to make a hash table efficient --averaging about 3 pointers worth of storage per entry, while a slot variable always only takes one. Therefore, any variable you can move into a slot represents a decrease in memory footprint, even if you can't move all of your variables into slots and still need __dict__. Plus, current versions of python don't actually create the underlying dictionary object that goes in __dict__ until a non-slot variable on the object is written to, so depending on the usage pattern of your code, it could actually be _more_ memory efficient to leave a set of variables that only a small fraction of the objects of some class will use out of __slots__ and just rely on the automatic creation of a __dict__ in those cases.

this channel is literally a gem im soooooo glad i found you

no useless words in the content, all are knowledge intensive explanation. perfect!

Love it! As a C / C++ dev (in past) I can appreciate this. However as u mentioned we are rarely memory constrained. Thx !

Nice. Your content is unique and not found anywhere else. Keep up the good work!

Its crazy how all your videos are intresting and easy to follow!

Thank you, your explanation was awesome! I've been doing Python for ages but never really bothered with __slots__. At least now, I know what they are, their trade-offs and what they're used for.

I'm working as a data scientist for 3 years using python with no-CS background and the topic you cover is always interesting and mindblowing.

Thanks, now i actually understand the previous video completely

Incredible as always...!!!

There's so much information, my brain is frying. I'll be looking back at your videos constantly!🤯

Love your tutorials. Great work! Subscribed

I would also like to thank you for sponsoring yourself.

I had been waiting on this! Really great you explain things well you are an explainer

Very clear explanation! Thank you very much :)

Best sponsorship in a vid I've seen

great video! I would like to see more c stuff , maybe even showing stuff on how python code translates to c code

That's the best sponsor spot ever!

I like your sponsorship very much :)

This is such a nice video! Thanks. Would love one on weakrefs or asyncio.

Love your videos keep it up!

I find not being able to add a member actually a very interesting feature. This is something I often don't want to do, but can happen by accident. Of course, mypy can catch that often.

Really interesting to me and useful. A debug through the C code would be very cool also.

Best python channel

what’s the recursive “getsize” function you use? great work as always!

I saw a comment on one of your videos saying "thanks Tony Hawk". Then I looked up Tony Hawk, and the comment suddenly made sense. Anyways, thanks for the videos.

I use __slots__ for a different reason. In the event that I write a new method and spell an attribute wrong, I find the bug immediately.

Really good video, as always. One request: can you do a video where you talk about making the Python classes in C? I use the CPython a lot to make modules (with only functions) in order to make faster codes. I was trying to make the Python classes directly from the C API but I have a lot of trouble. Thanks!

Really great explanation (as always!) Maybe a video on weakref in the future?

Excellent! Maybe one day I’ll use slots now 😅

I'm going to try to summarize what I learned in 1 paragraph, as I find it a helpful exercise, and I want to feed the algorithm :) When python classes store data, is uses a hashmap (__dict__). If you want to use an array of pointers instead, you accomplish this by specifying "__slots__". This has clear benefits if you care about the differences between these two data structures.

I remember I watched a talk from Richard Hettinger mentioning the use of __slots__ but he could not go into the details probably due to time constraints. Although I am not likely to use __slots__, thank you for making this video! I learn something new today! One question though: when we define a __dict__ in __slots__, does attribute assignments work the same as if __slots__ is not used? Is this __dict__ in the __slots__ of the superclass still a dictionary? And does Python uses this __dict__ when we assign new attributes dynamically to instances, if possible? Thank you!

This video format should be tried more at schools and universities.

This is GOLD

Can you create validator descriptors for classes with slots? It seems like setattr() and getattr() don't work the same.

what i miss from this video, is that, is the slots reserved for the variables you declare in "__init__" only or they go for the function definitions inside class themselves as well?

this guy rocks

What about the case when we will have a list object as a slot? Does that make sens?

I have a question: in my case I use fastapi with Pydantic classes for models, does using "__slots__" make any sense here? Or it not for my case?

Are there any nice tools that can visualize the memory layout of python objects just like your diagrams?

James -- what point were you making in the title, listing dunder-slots and slots separately? (BTW, nice choice of topic, and delivered satisfyingly succinctly.)

This for micro-controllers is very interesting

I haven’t used slots to save memory, but I have used to them to avoid a certain class of errors. I have some classes with writable properties. In particular, I had a property named “dash”. One day, I was writing code like ctx.dashes = «dash-settings» and I was wondering why the dash settings were not being correctly set. It took a while to realize I had written “dashes” instead of “dash”, and so instead of updating the correct property, Python had silently created an additional, useless, attribute! From that point, I have been careful to add slots definitions to such classes. However, if you then want to have weak references to instances of such classes, you must remember to add the name weakref to the slots list. This is where Python stores some kind of backpointer for keeping track of weak refs.

One tradeoff of slots that's not immediately apparent is that it can break multiple inheritance: A subclass can only have one parent class that defines nonempty slots. Presumably it has something to do with how parent and child slots are concatenated? Like in C++, for single inheritance you just tack on extra fields, and bam, the address of the child type is also valid as an address to the parent. But with multiple parents you need special casting operators. But since Python is using descriptors for access, I still don't quite get why that's an issue.

I feel like I can use this as using C Struct, where we already know its member ahead of time

"I'd like to thank *me*, for sponsoring *myself*! Did you know that I am available for consulting, contracting, training and interview prep services?" AWESOME

Just curious, is there any reason why you are using .__dict__ instead of vars()?

Great

what about '__dict__' AND '__weakref__' in __slots__? will the class be slotted WITH dictionaries and weakrefs?

Nice video! Now I finally understand slots in Python How can I get the sizes of ssize_t and ptr in Python? It would be nice to know where you search for information to prepare material for videos

So the size of a slot instance without recursion may be much larger then that of a normal instance without recursion.

Hey, do you know where I might be able to find a similar colour scheme for VS Code?

Yessir!

8:46 => could you explain Instance memory map for inherited class B(A), where A is slotted class but B is not.

So this makes classes more work like they do in C++,C# etc.Where you got predefined fields(instance variables) and you declare them static if you want them to be Class only.

That was like super awesome!

@0:34 #LOVEIT!! 🤣🤣🤣🤣🤣🤣👏👏👏👏

Are classes with slots faster? One fewer dictionary lookup must count for something, but is it noticeable in reasonable use cases?

This would be useful in the case of Cloud Functions where you have to pay for memory used by your program.

How do you calculate the recursive size of an object? Would like to see the `getsize()` function :)

How does changing a slots variable from an object instance work? I would assume that the value of that variable would change across all instances of that class. but it doesn't. can you explain why?

0:30 oh yeah good ol' me ;)

It seems like this slots thing should have been the default behavior of a class.... The ability to add attributes dynamically on-the-go is not the way most uses of classes are, even in python. I wonder why that's not the default, rather than the other way around, especially when it also saves on memory and although that's the standard case it is much less known.

Can you do a video on weakrefs? 🙏

Kudos on being full of yourself. What do you ask per hour of your time?

I've spent days trying to understand python code, which at runtime assigned attributes to objects, whose classes were also determined at runtime. Anything can be anything.

U consult also on Dart?

1. Is there a non-hacky way add type annotations to slotted attributes? 2. On 2:36 you say you can still add class variables to the class as usual. Can we go one level deeper and restrict that too ...with slots? ...without slots?

But those __slots__ pointers have to point to something - even if it's memory managed down at the C level (heap, presumably)?

Good video, but it doesn't really explain why slotted 7-attribute object is 5 times less memory demanding than the non-slotted one. In both cases we still need to store the data somewhere (either slot or a __dict__). Why storing data in __dict__ is so much more expensive? Where's all the additional memory consumption coming from? Genuine thank to anyone who takes time to explain me.

Will watch later Cause didnt have Time now

discord gang 😎

at 1:54 just to add some info to the viewers. This is monkey patching. Although usually we use it to change or add some method instead of just an attribute. Very pythonic!

Well, always have been a philosophical way of how to measure ones dict size correctly...

19th :D, yeah very specific ik

"I'd like to thank myself..."🤣🤣🤣🤣

Discord gang

Don't forget you hit the like button odd number of times in total, including all of your other visits to this video under the same KZfaq account.😇

I think this topic needs a bit of update regarding Python 3.11 objects with lazy dicts.

3rd

Hit that like button 5 times

1. I use MATLAB for work - and MATLAB doesn't allow assigning variables to classes on runtime by default. Does that mean it uses slots? (Is that the same for C++?) 2. So the class with slots stores the pointers to the data as an array? Where is the actual data stored?

0:30 just a moment i was expecting Snoop Dogg speech: kzfaq.info/get/bejne/ra2CeZZ4tpq7lJ8.html

Awesome video and great examples, but your face is too distracting 👀 Ye too handsome

Too many commas in that title

Help me

A hacker give this code to you def password(str_input, str_key): -> int Password_num = 0 str_key_len=len(str_key) str_input_len=len(str_input) for i in range(str_input_len): Password_num += str_key.index(str_input[i])*str_key_len**(str_input_len-i-1) return Password_num This function can take a string and output the password needed to protect the string Puzzle: Make a inverted function where argument are password and str_key Input: Line 1: password Line 2: str_key Output: A string Constrains: str_key cannot have duplicate letter and must have at least character within the str_input

HELP

If I could make a suggestion, your very well made videos might be even easier to follow if you used more descriptive names. Instead of calling a class "A" and and it's instance "a", calling them ClassA and inst_a could make it easier to follow as you speak. Just an idea.

this is amazing feature with horrible notation. Lets think about a decorator for that...

I love python but OOP in python is ugly

Did not work, so I googled it. Works if changed to: Class A(object):

actually, it can be an str itself (when you have only one attribute). check this out on documentation docs.python.org/3/reference/datamodel.html#object.__slots__ Transcripted from the reference: "This class variable can be assigned a string, iterable, or sequence of strings with variable names used by instances"

HELP