Python staticmethod and classmethod

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2 жыл бұрын

What are Python's staticmethod and classmethod?
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More importantly, how do they work? What are they good for? Let's find out all about staticmethods and classmethods.
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Пікірлер: 136

@QuantumHistorian 2 жыл бұрын

One thing that probably ought to have been mentioned alongside class methods are class variables. If you're only accessing class variables with a method, it's probably better to make it a class method. Makes it clear what you're doing and prevents accidentally overwriting class variables with method ones. But class variables aren't all that common to begin with, so this is kind of niche. Still, this is the only major use case outside of alternate constructors (and maybe singlets?) I can think of.

@mCoding 2 жыл бұрын

Yes thanks for pointing this out! In reality I pretty much never see this, but it's good to be prepared!

@Friedrich713 2 жыл бұрын

@@mCoding The scenario where I often fall back to using class variables is when I want to bundle some functionality together, but actually never need an instance of the class. Alternatively one could create a module (this would be the functional programming approach), but if the bundle is rather small, it's just a bit less convenient when importing.

@DrDeuteron 11 ай бұрын

I use class attributes all the time. Say, I have a constellation of 5 identical satellites, and my class holds their data. I'll handle the data in a base class, and each satellite gets a class color, or matplotlib position, so I can plot data clearly...for every orbit. There are other satellite dependencies that get handled a class attributes, like "bad channels", since thing break in space. Also: launch date, nominal equator crossing time, etc, etc....

@maxskoryk1466 2 жыл бұрын

I've been working on a task that has to do with constructing a class instance with additional arguments and couldn't wrap my head around how to do that without breaking the existing API. This video couldn't have come more timely: now that I know that there's such thing as classmethod, I'll explore a bit more about that, and I think this will be handy in solving my problem. THANK YOU for the excellent content!

@pavelkovalenko8845 2 жыл бұрын

I have been doing python for years now for research projects and uni homeworks. Basically been using with it almost all the time that I worked. I never got to learn these concepts tho despite trying a couple of times - all of the tutorials are either too basic or too specific to follow. This channel really fills that gap with flying colors, and I cannot stress enough how great of a find it is for me. Thanks, keep and up the good work!

@re.liable 2 жыл бұрын

I was just using staticmethods on my project the other day. I just like having the extra namespace for being more explicit 🙂 Cheers!

@VivekYadav-ds8oz 2 жыл бұрын

Yeah I can tell by your name 😂

@ciscoortega9789 2 жыл бұрын

What a coincidence, I just learned about staticmethod the other day! Great video, great explanations. Thanks very much.

@mCoding 2 жыл бұрын

Very welcome!

@ADFsoft 2 жыл бұрын

One reason to use static method is that they are inherited and can be re-defined in sub-classes.

@lawrencedoliveiro9104 2 жыл бұрын

That’s true of all methods. Oh, you mean in place of top-level functions?

@elefantsnablar 2 жыл бұрын

2:23 Been searching for a good explanation of why one typically uses classmethod instead of staticmethod for alternative constructors. This explained it perfectly. Thanks!

@akshatsrivastava3379 2 жыл бұрын

The black hole joke was funny

@lphillis1 2 жыл бұрын

These videos are amazing for intermediate level Python programmers and professional use. Keep making more!

@mCoding 2 жыл бұрын

That's the goal! See you in the next one! (Or maybe in a previous one first?)

@mattlau04 2 жыл бұрын

Really helpful to learn what the use cases might be !

@Jakub1989YTb 2 жыл бұрын

Becoming a KZfaq Python legend, one video at a time. Great work. I'm, so glad I found your channel in it's "early" stage. I dig you'r thumbnails too. Simple, but class Y:.

@mCoding 2 жыл бұрын

Glad to have you aboard! I'm amazed you call it the early stage! I remember when I had 30 videos and only 29 subscribers, that was the early stage for me!!

@shashishekhar---- Жыл бұрын

Thank you for such a helpful video James! , much appreciated brother 👍🏼👏🏽

@ciberman Жыл бұрын

I'm a C# developer learning python and I was very confused because there aren't any similar things like class methods in C# or any other mainstream OOP language (Ts, java, etc). So this video helped me a lot. Thank you!

@orisphera 2 жыл бұрын

For the matrices, I think it's better to do this: class Matrix: ... def can_multiply(self, other): ... and use a.can_multply(b). This way, you don't have to make a map from classes to functions or use things like type(a).__module__.can_multiply(a, b) to check if you can multiply two variables of unknown type.

@PeterZaitcev Жыл бұрын

AND you still can call it Matrix.can_multiply(a, b)

@anthonyrogers9849 2 жыл бұрын

Thanks for this. I have never used static methods myself and have sometimes wondered if I was missing an important use case. Guess not!

@alexd7466 2 жыл бұрын

A good thing to realize is that editors like Pycharm indicate there is something wrong with a method when the method does not use any instance or class variables, and showing the message "could be static". This causes a lot of confusion for beginning programmers who then change all methods to @staticmethods.

@HonsHon 2 жыл бұрын

Idk why but I actually like Visual Studio Code better for Python

@Eclipse_co5mic Жыл бұрын

this was truly amazing. THANK YOU

@reddragon3132 2 жыл бұрын

A random use case for static methods I found was when parallelising code. If I call an instance method, the whole instance object would be passed to the child process - a massive overhead that caused pretty much negated the parallelisation gains. A static method allowed passing of only the required attributes to process

@kevinz1991 2 жыл бұрын

Really great stuff thank you so much for making this

@RecursiveTriforce 2 жыл бұрын

It's just the arguments that change. normal: self, *args @classmethod: cls, *args @staticmethod: *args @property: self

@nigh_anxiety 2 жыл бұрын

It wasn't mentioned, but I think another reason you might call a class method from an instance is if your instance was created from a factory based on an ABC or Protocol, so all of the classes have the same class method with potentially different content. Although in that case maybe its still better to have an instance method which wraps the class method.

@khalilrouatbi6345 2 жыл бұрын

clear and straight to the point!

@MrSteini124 2 жыл бұрын

Great as always, thanks

@expirytrader5802 2 жыл бұрын

One of the best videos of your I really like it.

@AJ-et3vf Жыл бұрын

Great video. Thank you

@mauriciolomeli2940 2 жыл бұрын

The ending brought so much nastalgia (e.g. binding). Thank you!

@robertbrummayer4908 2 жыл бұрын

Excellent video

@marcgentner1322 Ай бұрын

love the full and simple explanaition. i use staticmethods when appling MVC structure to my api's from the user_model UserModel class i need only sertain methods from the UserModel class. so i can call whathever query method i need in my controllers.

@loucadufault6549 2 жыл бұрын

I got asked the difference between the two on an interview question last week!

@Aang139 Жыл бұрын

My main use cases for static methods have been polymorphic work that doesn't need access to the cls or instance beyond variations in the type (rarest case), or serializer classes that use methods to (de)serialize a single field (i don't need the serializer class just the day passed in), or unit test classes

@vikranttyagiRN 2 жыл бұрын

Thanks for the video. Although I am gonna have to watch it a couple of times to let it all sink in.

@sharkinahat 2 жыл бұрын

Very nice video. I sometimes think staticmethod was added to please programmerd comming from Java.

@ConsuelaPlaysRS 2 жыл бұрын

I'd like to see a video about the 'global' and 'nonlocal' statements in python where you detail legitimate cases for when they can sensibly be used

@MultiCraftTube 2 жыл бұрын

I really enjoy learning new stuff in Python on this channel, but I wonder how usefull all of this is. Are there any enterprises operating on Python? :D

@th_sajal 2 жыл бұрын

Could you comment on what's the size of a class, like an empty class or the one containing some class variables. How does these differ, kind of memory allocation that happens during compilation?

@CaptainCsaba 2 жыл бұрын

So when constructing a pandas DataFrame with the read_excel, read_csv or from_records etc, those are classmethods?

@mCoding 2 жыл бұрын

Actually pandas makes them all freestanding functions. I guess they expect that you don't ever inherit from a DataFrame.

@zakyvids6566 2 жыл бұрын

Hi James this is a very good channel I was wondering can you please make a 30 minute python crashcourse covering the basics of python I’m new to coding and wish to watch a short chars course from your channel as it’s very clear and concise simple to follow Please consider my request Thanks

@anthonyaouad4190 2 жыл бұрын

Hey, I suggest watching Corey Schafer he has some good tutorials for beginners. However they are longer than 30 mins!

@ThijmenCodes 2 жыл бұрын

Great info, thanks. I use static methods all the time, but I never knew that a class method was a thing!

@mCoding 2 жыл бұрын

Glad it was helpful!

@ahasibrifat7568 2 жыл бұрын

Thanks

@makhdv 2 жыл бұрын

would be nice to mention on typing more. Using mypy can_multiply(a: Matrix, b: Matrix) would have a nice context, imho. And is it always factory class methods, returning instance of class to keep inheritance, should become Generic[T] where T Calendar subclass, like ‘def from_json(cls, …) -> ???:’ ?

@its_code 2 жыл бұрын

WOW 😳 amazing information. Love 💕 from Pakistan

@mCoding 2 жыл бұрын

Thanks for watching!

@lawrencedoliveiro9104 2 жыл бұрын

1:36 In certain countries, the weekend is Thursday and Friday. There is at least one country 🇲🇾, where certain states observe this rule, while others observe a Saturday/Sunday weekend. Now imagine the fun of different branches of some organization, operating in different states, trying to decide when you can make a call to another branch and expect somebody to answer ...

@mCoding 2 жыл бұрын

I think that writing a datetime library would probably be the hardest library to write that seems like it would be easy at first glance.

@joseville 2 жыл бұрын

3:43 any thoughts on type(self).classattr vs self.__class__.classattr ?

@danielderwertvolle6354 2 жыл бұрын

0:57 "But sometimes when you write a method you don't really care about the specific instance of a class or maybe you don't have a specific instance yet. That's a good signal that what you are doing is..." applying OOP when you really shouldn't.

@mCoding 2 жыл бұрын

Sometimes, maybe! But let's not confuse using classes with using OOP.

@lawrencedoliveiro9104 2 жыл бұрын

2:16 Should answer your argument.

@DrDeuteron 11 ай бұрын

definitely use class methods as constructor helpers: do not do work in dunder init! It should just initialize instance attributes.

@norude 2 жыл бұрын

2:23 ... and that exactly what happens with any immutable class, that has something like __add__, because you can not make method both *class* and *instance* Also you can not inherit from int for same reasons

@aadithyavarma 2 жыл бұрын

Amazing video! But why is Sunday given as "U" in your is_weekend() method?

@homelikebrick42 2 жыл бұрын

because then there would be 2 "S" days?

@atrus3823 2 жыл бұрын

@@homelikebrick42 Thursday is also often an R when using single letter abbreviations of weekdays.

@hanyanglee9018 2 жыл бұрын

Since python is not static typed, a C.method() is not better than method(). But in static typed lang, such as c++, C.method() is much easier to remember and write, all you need to do is to remember C.me*, write C. and wait for the compiler and find the function start with me. In python, this trick is not stable even if you work with pycharm.

@lawrencedoliveiro9104 2 жыл бұрын

3:09 This can only work in a language where classes are first-class objects!

@nurkleblurker2482 2 жыл бұрын

But wouldn't the class always be the same because the method is defined in a class? If cls is identical to type(self) then how is a class method useful?

@not_vinkami 2 жыл бұрын

1:33 "assuming of course we're ignoring people that live close to black holes." Physicists love this assumption

@vekyll 2 жыл бұрын

5:50 The fact that you aren't aware of something doesn't mean it doesn't exist. Static methods do have their valid usage, and although rare, it does occur and I've needed it one or two times in my programming career. It happens when you have e.g. a subclass B of class A, and it overrides the method m which doesn't depend on the specific instance--but of course it does depend on the class itself. For example, if you had IslamicCalendar, it would of course redefine what is_weekend means, but it would still be a static method.

@mCoding 2 жыл бұрын

Hi no need for the offensive tone on this channel. Your example is not one I would recommend using a staticmethod for.

@vekyll 2 жыл бұрын

@@mCoding "When you do use them, the justification for doing so is shaky at best" - do you consider that to be offensive tone? Again, telling me you don't like what I told you doesn't solve anything. What _would_ you recommend?

@oddzhang 2 жыл бұрын

5:40 what is "context" exact meaning in Python with the static method

@terencetsang9518 2 жыл бұрын

He just meant the location the function is defined and its surroundings - nothing to do with the Python concept of context (manager). On its own the name `can_multiply()` may mean anything, but defining it as either a static method in some `Matrix` class, or a function in some `matrix` module, makes it clear that the function is meant to be used with matrices.

@oddzhang 2 жыл бұрын

@@terencetsang9518 Thanks, I supposed to get it.

@kyle-silver 2 жыл бұрын

Sometimes I use static methods for “private” class methods. If there’s some function specific to the class that happens to be static but I don’t want to expose as part of the public api, I think it’s a good way to signal “this functionality shouldn’t be used elsewhere”

@aadithyavarma 2 жыл бұрын

In python, one way to hint that a method is "private" is by using a single underscore. def _private_foo(self): pass The notion is that, this method should not be used outside the class it is defined.

@atrus3823 2 жыл бұрын

I think get what you're saying, but I don't think "private" is the correct term. And by public API, I assume you mean the module API? Static methods still exist in the class' public API. Like, if it was a module function, it implies that it can be used in any case where it applies, but if it is static, it implies that it should only be used with that class?

@aadithyavarma 2 жыл бұрын

@@atrus3823 When you make a method, a staticmethod, it means that the method will not be using any other variables or methods of the class it is in, but still makes sense to be inside the class due to the staticmethod doing something related to what the class is supposed to do. You can call the staticmethod with the class or the object of the class, outside the class and it still is valid and makes sense. If you want to make the method seem "private" meaning it does not make sense to use it outside the class, then adding a single "_" at the beginning of the method is the pythonic way to do it. In short, static and private are two independent features imo.

@atrus3823 2 жыл бұрын

@@aadithyavarma Why are replying this to me? Did you mean to reply to the original post?

@bartomiej368 2 жыл бұрын

@@aadithyavarma i think he meant that (what i also do) that there are "helper" methods that are both private and static, when you need apply set of instructions on data, like formating, but don't want to write it several times.

@friedkeenan 2 жыл бұрын

For implementing classmrthod, you can also just call the constructor of types.MethodType which I find to be cleaner and more readable than calling `__get__` on the underlying function

@atrus3823 Жыл бұрын

I got a notification of a reply to a comment of mine, but now it seems to be gone. Was it deleted? If so, why?

@mCoding Жыл бұрын

Wasn't me, probably yt auto spam filter.

@atrus3823 Жыл бұрын

@@mCoding oh well! Stuff happens 🤷

@therandomsomeone. 2 жыл бұрын

this channel has only one purpose it is to make overviews of python decorators

@MithicSpirit 2 жыл бұрын

Discord gang

@zbaktube Жыл бұрын

at line 12, why Sunday is encoded as 'U'?

@mCoding Жыл бұрын

Because sunday and saturday both start with S, it is common to represent sunday with U.

@zbaktube Жыл бұрын

@@mCoding I see, and 'T' 's are OK as they are not next to each other, aren't they?

@zbaktube Жыл бұрын

@@mCoding By the way, thanks, I did not know that

@pavelx6411 2 жыл бұрын

Discord!!!!

@trag1czny 2 жыл бұрын

discord gang 🤙🤙

@Sonyim414 2 жыл бұрын

More like opened my KZfaq now gang

@p_square 2 жыл бұрын

🤝

@manikandanraju3673 2 жыл бұрын

Hi James, Good day to you.. I have been following your channel for quite some time. It was very helpful to understand unfamiliar python concepts. Could you pls make a video on UDP/TCP packets logging and manipulation with python. Love from India

@mCoding 2 жыл бұрын

Suggestion noted! Though if i were to cover tcp or udp it would probably be a C or C++ video as python would struggle with such primitives.

@aonodensetsu 2 жыл бұрын

static methods are great, you can import the class and then know that Matrix.can_multiply is a function from the matrix file, instead of importing * and having a random can_multiply function in your namespace

@vekyll 2 жыл бұрын

Static methods really are great, but 1) you're mixing classes and files, this is not Java where they are the same, 2) can_multiply is in fact an ordinary method, since a (and also b) is a Matrix. So yes, it is a good example of a method, but not of a static method.

@joeyv8197 5 ай бұрын

Im in the middle of a python course and have been watching plenty of videos and a show about programming, how long did anyone else take to catch on?

@mCoding 5 ай бұрын

Keep at it! It can take years to see the importance of some of my videos, don't let them drag you down. Just keep coding and build stuff that interests you. The stuff that matters will become apparent through experience over time.

@joeyv8197 5 ай бұрын

@@mCoding I'm def not expecting to get a job anytime soon but I have learned a lot and only a 3rd of the way through the course!

@sdprogrammers 2 жыл бұрын

Static variable

@masheroz 2 жыл бұрын

Would class methods cease to be a thing if there were the possibility of multiple constructors?

@alexd7466 2 жыл бұрын

creating alternative constructors is precisely why classmethods exists.

@masheroz 2 жыл бұрын

@@alexd7466 then why not just have multiple constructors?

@alexd7466 2 жыл бұрын

@@masheroz We have 3 ways to create alternative constructors already, and you still need more?

@MrTyty527 2 жыл бұрын

assume that they do not live near black holes. very important assumption indeed

@cristobaljvp 2 жыл бұрын

Lately I've been reading big libraries and classmethods are used a lot. I actually haven't need them until now, but I hope I can get the opportunity to use them. Good video as always. Thanks for the content!

@26-dimesional_Cube 2 жыл бұрын

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

@oamioxmocliox8082 2 жыл бұрын

;)

@markcuello5 Жыл бұрын

HELP

@codingcrashkurse6429 2 жыл бұрын

I always learned: If you think about using a static method, you probably don´t want that method in your class. Can anyone proofe me wrong here?

@sadhlife 2 жыл бұрын

He explained it in the video with the "is_weekend" function. Staticmethods can be useful to provide context to the programmer that the function belongs to a class. Even if it doesn't need to be in it.

@QuantumHistorian 2 жыл бұрын

I just like having things in a namespace. I also use it if the function is exclusively called by methods of a particular class. It's then a sign that says "You're not going to need this elsewhere, don't worry about it". Because when I read a module, I tend to read more carefully the standalone functions as things that I might want to call from outside the module. Burying something as an static method avoids that, and can mean that a method is defined close to where it's called, which further improves readability. But yes, it's a minor stylistic thing, and it can "softlock" future widening of scope.

@SachinShukla230187 5 ай бұрын

Confusing......

@benvan3721 26 күн бұрын

thanks. but not right for a beginner learner. It's like reading a file

@jonobrien8848 Жыл бұрын

static methods should just not be in the class since they don't use self.

@obed818 2 жыл бұрын

Dont you want learn french language my friend ?

@obed818 2 жыл бұрын

😣

@adityahpatel 2 ай бұрын

this is not a good example to illustrate of. Confuses more than simplifies

@Nieosoba Жыл бұрын

eee sorry but not very good explanation, but thanks anyway

@mCoding Жыл бұрын

Hello fellow person with an m avatar 👀. Perhaps you would enjoy my video on descriptors instead?

@dDANiLiCHh Жыл бұрын

boring.

@mCoding Жыл бұрын

lol i don't disagree

@dhuhacorp9372 Жыл бұрын

Your explanation is jumping everywhere and make me confuse

@IndellableHatesHandles 2 жыл бұрын

Jeez, Python is becoming a patchwork. I find Java annotation-like syntax like this to be ugly. It doesn't fit Python at all.

@lawrencedoliveiro9104 2 жыл бұрын

Decorators are not “annotations”. They are actual function calls.

@squeezyfranky620 2 жыл бұрын

Why are you using pseudocode for teaching? In my opinion this video needs executing and real code. it's not that hard. For me as a beginner it took а few hours to uderstand what's realy going on with my own code. Please, add some more executing. It will make content so much easier to understand

@markcuello5 Жыл бұрын

HELP