Python __slots__ and object layout explained

Save memory using Python slots.

Python __slots__ are useful for saving memory when you have a large number of small objects whose attributes are known ahead of time. In this video we learn about __slots__, what slots actually are and how they work.

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CHAPTERS
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0:00 Intro
0:43 Normal class
1:53 Slots class
2:44 Why use slots
4:21 Slots are descriptors
5:45 What are slots
8:32 Inheritance
9:14 No metaclass slots
9:24 Using a dict slot

[AWriterWandering]

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

[Yotanido]

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.

[alcyonae]

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

[strandingstranger]

this channel is literally a gem im glad i found you

[AJMansfield]

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.

[mike]

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

[goeiecool]

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

[rickharold]

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

[Roarshark]

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.

[vinson]

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.

[phuctran]

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

[MaxTechniche]

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

[n-ds]

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.

[davea]

I would also like to thank you for sponsoring yourself.

[laurinneff]

Thanks, now i actually understand the previous video completely

[NStripleseven]

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

[AsgerJon]

That's the best sponsor spot ever!

[ipbody]

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

[טלאיצקוביץ-במ]

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

[Mustak]

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!