I'm wondering if there is a way to make the referencing of static variables more convenient in a base class by defining some type of static reference to the derived class type?
Note: code edited after posting
class base:
MainType = None
StaticVariables = xyz
def Func(self):
base.MainType.StaticVariables = 0
class derived(base):
base.MainType = THISCLASS # pseudo code - no idea how to do this
I hope this isn't too confusing. I've read that you need to use type(self).StaticVariables to access any static variables, so I was hoping there may be some way to record the derived class type ahead of time to make them more accessible. Is something like this possible? Or is it a bad idea? I'm also curious to know if its possible to access the type of a class that is being defined. Is there any equivalent to 'self' for types (rather than instances) while outside of functions?
Edit: Have yet another question in case anyone is browsing by and sees this. When a base class defines a static variable, does this static variable get duplicated for each derived type, or does only one version of it exist regardless of the number of derived types?
If I understand you correctly, this is what classmethod is for:
class Base():
name = 'base'
#classmethod
def say_hi(cls):
print(f'Hi from {cls.name}!')
class Derived(Base):
name = 'derived'
Base().say_hi()
Derived().say_hi()
Output:
Hi from base!
Hi from derived!
Instead of taking a reference to the current instance, in the form of self, classmethods take a reference to the type of the current instance, through some nice decorator magic. This lets you call them like normal methods without having to scatter type(self) all over the place.
i created this class for my homework:
class sayfa():
isim=" "
def __init__(self,bSayisi,ySayisi,pSayisi,iSayisi,tSayisi):
self.bSayisi=bSayisi
self.ySayisi=ySayisi
self.pSayisi=pSayisi
self.iSayisi=iSayisi
self.tSayisi=tSayisi
if ((((bSayisi+ySayisi+pSayisi)/iSayisi)/tSayisi)*100)>0.2:
print(isim,"başarılı")
else:
print(isim,"başarısız")
then i called it in another .py file:
from eRate import sayfa
ybs1=sayfa(365000,65000,870,500,1125000)
ybs1.isim="YBS-1"
then i tried to work it and it gave me this error:
NameError: name 'isim' is not defined
I think i did something wrong when i'm writing class but i don't know what i actually done wrong.Can you help me?
edit:
My code worked when i put isim variable in def init but it looks weird.It looks like this:
class sayfa():
def __init__(self,bSayisi,ySayisi,pSayisi,iSayisi,tSayisi,isim):
self.isim=str(isim)
self.bSayisi=bSayisi
self.ySayisi=ySayisi
self.pSayisi=pSayisi
self.iSayisi=iSayisi
self.tSayisi=tSayisi
if ((((bSayisi+ySayisi+pSayisi)/iSayisi)/tSayisi)*100)>0.2:
print(isim,"başarılı")
else:
print(isim,"başarısız")
and when i'm adding data in class it gets weirder:
from eRate import sayfa
ybs1=sayfa(365000,65000,870,500,1125000,"YBS-1")
The error isn't with the way you're assigning things, but with the way you're accessing them.
Just as you have to do self.bSayisi to set an attribute, you have to do self.isim to access one. So:
print(self.isim, "başarılı")
(and the same for the other line…)
If you're wondering why you were able to access other values like bSayisi without self.bSayisi—that's just because you happen to have a parameter named bSayisi that happens to have the same value as self.bSayisi (because you just made that true a few lines earlier). If you changed it to, say, self.bSayisi = bSayisi*2, or you renamed the parameter to myBSayisi and did self.bSayisi = myBSayisi, you'd see that just using bSayisi instead of self.bSayisi was no longer correct.
However, while this eliminates the error, I'm not sure it actually does what you want. At the time you're doing this print, you haven't assigned an isim value to the object yet, so it's going to get the class value as a default, so it's always just going to be " ". Is that really what you wanted?
If not, you need to move the print calls to some other method that you can call later, after having assigned isim. For example:
class sayfa():
isim=" "
def __init__(self,bSayisi,ySayisi,pSayisi,iSayisi,tSayisi):
self.bSayisi=bSayisi
self.ySayisi=ySayisi
self.pSayisi=pSayisi
self.iSayisi=iSayisi
self.tSayisi=tSayisi
def displaystuff(self):
if ((((self.bSayisi+self.ySayisi+self.pSayisi)/self.iSayisi)/self.tSayisi)*100)>0.2:
print(self.isim,"başarılı")
else:
print(self.isim,"başarısız")
ybs1=sayfa(365000,65000,870,500,1125000)
ybs1.isim="YBS-1"
ybs1.displaystuff()
Of course moving the isim into the constructor works, by avoiding the problem you were running into. It's not an answer to how to add data after the __init__ method, of course, because you're instead adding the data in the __init__ method. When that's appropriate, it's the simplest answer.
But if it looks weird in this case (I'll take your word for it; I don't know exactly what this code is trying to do), it's probably the wrong answer for this particular class.
In which case, you do need to know how to add data after the __init__ method, as you asked. Or, rather, you need to know how to access that data—because you were already adding it correctly.
This is the difference between class attributes (when it is outside of the __init__ with no self.) and instance attributes (when you added it inside the __init__ with the self.).
Class attributes are a little more complicated since they pertain to all the instances of that class (you could overwrite them within some instances, but then they'd become instance attributes in those cases)... and so if you changed a class attribute, it would affect all other instances you may have created or will create in the future.
For a more in-depth discussion of class attributes vs instance attributes see this answer that summarizes this post.
Normall __init__(..) is used to initialize / instantiate your instance. I would not print in it, nor calculate (unless you calculate some other class-variables and set them).
You need to prefix your variables of the instance by self. and the static class variable with the class name to acess it:
class sayfa():
isim=" " # this is a shared class variabl (aka static)
def __init__(self,bSayisi,ySayisi,pSayisi,iSayisi,tSayisi):
self.bSayisi=bSayisi # these are all instance variables, not shared
self.ySayisi=ySayisi
self.pSayisi=pSayisi
self.iSayisi=iSayisi
self.tSayisi=tSayisi
self.unusedSum = ySayisi + pSayisi + iSayisi
def printMe(self): # lookup __str__() and __repr__() for how to output your instance
if ((((self.bSayisi+self.ySayisi+self.pSayisi)/self.iSayisi)/self.tSayisi)*100)>0.2:
print(sayfa.isim,"some text") # use the static class variable
else:
print(sayfa.isim,"some other text")
sayfa.isim = "Coffee " # you set static class variables by prefixing class name
my_sayfa_instance = sayfa(365000,65000,870,500,1125000)
other_sayfa_instance = sayfa(3600,65000,870,500,10)
my_sayfa_instance.printMe()
other_sayfa_instance.printMe()
Output:
Coffee some other text
Coffee some text
I need to access a variable from a nested class. The objective is to create a Schema using the Marshmallow library. The code looks like this :
class ParserScheme(Schema):
class Meta:
# Here I meed to access the value of my_variable :
result = func(my_variable)
my_variable = 'foo'
my_parser = ParserScheme()
If I manage to pass my variable as a class attribute of the outer class (ParserScheme), then it is easy to get it into the inner class (Meta).
class ParserScheme(Schema):
class_attribute = my_variable
class Meta:
result = func(ParserScheme.class_attribute)
my_variable = 'foo'
my_parser = ParserScheme()
However I can't seem to find a way to dynamically set a class attribute. And if I set a "classic" attribute (I mean an attribute of instances of the class, not of the class itself), then I can't access it from the inner class.
I also thought of using a global variable, but that does not really quite satisfy me. Is there another way of doing this ?
I am rather new to OOP, and I am not sure I understand really well the concept of class attribute. I fear that there is an easy way to do that but I did not see it as I am to focused on the way I think this should work...
Your first example breaks because name my_variable is not yet defined when the class Meta statement's body is executed.
You second example won't work either for the same reason (my_variable is not yet defined when the class ParserScheme statement's body is executed), and if it was it would still break when executing the class Meta statement's body because it will be executed as part of the class ParserScheme statement's body hence before the name ParserScheme is defined.
What you have to understand here is that class and def are executable statements which (if at the top level of a module) are executed sequentially when the module is first imported into the current process. In the case of a class statement, the statement's body is first sequentially executed in a dedicated namespace then this namespace is passed to the metaclass constructor and used to create the class object's attributes (YourClass.__dict__).
To make a long story short: in a class statement body, you just cannot reference names that are not yet defined in the current or enclosing scope. Period.
The obvious solution here would be to define my_variable before the class statement, but I assume you want it to be more dynamic ? If yes, you'll have to define your class in a function:
def create_parser_class(my_variable):
class ParserScheme(Schema):
class Meta:
result = func(my_variable)
return ParserScheme
my_variable = 42
cls = create_parser_class(my_variable)
my_parser = cls()
But I can't garantee it will work out of the box (nor even work at all FWIW) with Marshmallow (which I never used but probably has some metaclass stuff happening). Also depending on what my_variable is used for, you may want to make sure you don't have two calls to create_parser_class with the same value as argument.
As a last note : you perhaps have a XY problem here - that's sometimes the case when someone asks how to do something a bit non-obvious or unusual. Perhaps you should edit your post to explain the "problem behind" - that is, the problem you are actually trying to solve with this "solution".
Oh and yes:
I am rather new to OOP, and I am not sure I understand really well the concept of class attribute
In Python, classes are objects too (instances of their metaclass, by default the type object), and as such they have their own attributes. Every name you define (with an assignment, a def statement, a class statement or an import statement) at the top-level of the class statement becomes an attribute of the class object (unless a custom metaclass makes some transformations on the way, that is).
Class attributes are accessible from the instances too (unless shadowed by an eponym instance variable), and are shared between all instances.
I know the question header sounds weird, but since English is not my first language, I find it very hard to formalize. However, I might be able to explain it with bit more text.
The problem is, that I'm trying to create a class called "Foo" for example.
# ../myProject/Foo.py
class Foo:
'''Represents an example class for stackoverflow'''
Now all of Foo class' instances have function attribute, which simply holds a function which can be executed via the instance. Also, there's a parameters attribute, a tuple or a list, which holds parameters which should be used when the function gets called.
def __init__(self, function, parameters):
self.function = function
self.parameters = parameters
def callFunction(self):
if self.function:
self.function(*self.parameters)
This seems to be working fine, however, the problem is, that I want to give it a default value, to change an attribute of the instance. I basically wanna do the following:
def __init__(self, function=setattr, \
parameters=(self, "togglableAttribute", not self.togglableAttribute)):
And doing this will raise NameError: name 'self' is not defined. How should I implement this in order for it to work, or should I come up with a workaround?
self is the typical variable name used to describe the instance. However, default arguments are evaluated when the function is created (at class creation time). Of course self doesn't exist yet because the class doesn't even exist yet -- The class is still in the process of being built.
The typical way to do this is to check for a sentinel;
def __init__(self, function=setattr, parameters=None):
if parameters is None:
parameters = (self, "togglableAttribute", not self.togglableAttribute)
See my answer here (and the comments below it) for a discussion of various objects that you can use as your sentinel and the various pros and cons of each.
I'm teaching myself Python and my most recent lesson was that Python is not Java, and so I've just spent a while turning all my Class methods into functions.
I now realise that I don't need to use Class methods for what I would done with static methods in Java, but now I'm not sure when I would use them. All the advice I can find about Python Class methods is along the lines of newbies like me should steer clear of them, and the standard documentation is at its most opaque when discussing them.
Does anyone have a good example of using a Class method in Python or at least can someone tell me when Class methods can be sensibly used?
Class methods are for when you need to have methods that aren't specific to any particular instance, but still involve the class in some way. The most interesting thing about them is that they can be overridden by subclasses, something that's simply not possible in Java's static methods or Python's module-level functions.
If you have a class MyClass, and a module-level function that operates on MyClass (factory, dependency injection stub, etc), make it a classmethod. Then it'll be available to subclasses.
Factory methods (alternative constructors) are indeed a classic example of class methods.
Basically, class methods are suitable anytime you would like to have a method which naturally fits into the namespace of the class, but is not associated with a particular instance of the class.
As an example, in the excellent unipath module:
Current directory
Path.cwd()
Return the actual current directory; e.g., Path("/tmp/my_temp_dir"). This is a class method.
.chdir()
Make self the current directory.
As the current directory is process wide, the cwd method has no particular instance with which it should be associated. However, changing the cwd to the directory of a given Path instance should indeed be an instance method.
Hmmm... as Path.cwd() does indeed return a Path instance, I guess it could be considered to be a factory method...
Think about it this way: normal methods are useful to hide the details of dispatch: you can type myobj.foo() without worrying about whether the foo() method is implemented by the myobj object's class or one of its parent classes. Class methods are exactly analogous to this, but with the class object instead: they let you call MyClass.foo() without having to worry about whether foo() is implemented specially by MyClass because it needed its own specialized version, or whether it is letting its parent class handle the call.
Class methods are essential when you are doing set-up or computation that precedes the creation of an actual instance, because until the instance exists you obviously cannot use the instance as the dispatch point for your method calls. A good example can be viewed in the SQLAlchemy source code; take a look at the dbapi() class method at the following link:
https://github.com/zzzeek/sqlalchemy/blob/ab6946769742602e40fb9ed9dde5f642885d1906/lib/sqlalchemy/dialects/mssql/pymssql.py#L47
You can see that the dbapi() method, which a database backend uses to import the vendor-specific database library it needs on-demand, is a class method because it needs to run before instances of a particular database connection start getting created — but that it cannot be a simple function or static function, because they want it to be able to call other, supporting methods that might similarly need to be written more specifically in subclasses than in their parent class. And if you dispatch to a function or static class, then you "forget" and lose the knowledge about which class is doing the initializing.
I recently wanted a very light-weight logging class that would output varying amounts of output depending on the logging level that could be programmatically set. But I didn't want to instantiate the class every time I wanted to output a debugging message or error or warning. But I also wanted to encapsulate the functioning of this logging facility and make it reusable without the declaration of any globals.
So I used class variables and the #classmethod decorator to achieve this.
With my simple Logging class, I could do the following:
Logger._level = Logger.DEBUG
Then, in my code, if I wanted to spit out a bunch of debugging information, I simply had to code
Logger.debug( "this is some annoying message I only want to see while debugging" )
Errors could be out put with
Logger.error( "Wow, something really awful happened." )
In the "production" environment, I can specify
Logger._level = Logger.ERROR
and now, only the error message will be output. The debug message will not be printed.
Here's my class:
class Logger :
''' Handles logging of debugging and error messages. '''
DEBUG = 5
INFO = 4
WARN = 3
ERROR = 2
FATAL = 1
_level = DEBUG
def __init__( self ) :
Logger._level = Logger.DEBUG
#classmethod
def isLevel( cls, level ) :
return cls._level >= level
#classmethod
def debug( cls, message ) :
if cls.isLevel( Logger.DEBUG ) :
print "DEBUG: " + message
#classmethod
def info( cls, message ) :
if cls.isLevel( Logger.INFO ) :
print "INFO : " + message
#classmethod
def warn( cls, message ) :
if cls.isLevel( Logger.WARN ) :
print "WARN : " + message
#classmethod
def error( cls, message ) :
if cls.isLevel( Logger.ERROR ) :
print "ERROR: " + message
#classmethod
def fatal( cls, message ) :
if cls.isLevel( Logger.FATAL ) :
print "FATAL: " + message
And some code that tests it just a bit:
def logAll() :
Logger.debug( "This is a Debug message." )
Logger.info ( "This is a Info message." )
Logger.warn ( "This is a Warn message." )
Logger.error( "This is a Error message." )
Logger.fatal( "This is a Fatal message." )
if __name__ == '__main__' :
print "Should see all DEBUG and higher"
Logger._level = Logger.DEBUG
logAll()
print "Should see all ERROR and higher"
Logger._level = Logger.ERROR
logAll()
Alternative constructors are the classic example.
It allows you to write generic class methods that you can use with any compatible class.
For example:
#classmethod
def get_name(cls):
print cls.name
class C:
name = "tester"
C.get_name = get_name
#call it:
C.get_name()
If you don't use #classmethod you can do it with self keyword but it needs an instance of Class:
def get_name(self):
print self.name
class C:
name = "tester"
C.get_name = get_name
#call it:
C().get_name() #<-note the its an instance of class C
When a user logs in on my website, a User() object is instantiated from the username and password.
If I need a user object without the user being there to log in (e.g. an admin user might want to delete another users account, so i need to instantiate that user and call its delete method):
I have class methods to grab the user object.
class User():
#lots of code
#...
# more code
#classmethod
def get_by_username(cls, username):
return cls.query(cls.username == username).get()
#classmethod
def get_by_auth_id(cls, auth_id):
return cls.query(cls.auth_id == auth_id).get()
I think the most clear answer is AmanKow's one. It boils down to how u want to organize your code. You can write everything as module level functions which are wrapped in the namespace of the module i.e
module.py (file 1)
---------
def f1() : pass
def f2() : pass
def f3() : pass
usage.py (file 2)
--------
from module import *
f1()
f2()
f3()
def f4():pass
def f5():pass
usage1.py (file 3)
-------------------
from usage import f4,f5
f4()
f5()
The above procedural code is not well organized, as you can see after only 3 modules it gets confusing, what is each method do ? You can use long descriptive names for functions(like in java) but still your code gets unmanageable very quick.
The object oriented way is to break down your code into manageable blocks i.e Classes & objects and functions can be associated with objects instances or with classes.
With class functions you gain another level of division in your code compared with module level functions.
So you can group related functions within a class to make them more specific to a task that you assigned to that class. For example you can create a file utility class :
class FileUtil ():
def copy(source,dest):pass
def move(source,dest):pass
def copyDir(source,dest):pass
def moveDir(source,dest):pass
//usage
FileUtil.copy("1.txt","2.txt")
FileUtil.moveDir("dir1","dir2")
This way is more flexible and more maintainable, you group functions together and its more obvious to what each function do. Also you prevent name conflicts, for example the function copy may exist in another imported module(for example network copy) that you use in your code, so when you use the full name FileUtil.copy() you remove the problem and both copy functions can be used side by side.
Honestly? I've never found a use for staticmethod or classmethod. I've yet to see an operation that can't be done using a global function or an instance method.
It would be different if python used private and protected members more like Java does. In Java, I need a static method to be able to access an instance's private members to do stuff. In Python, that's rarely necessary.
Usually, I see people using staticmethods and classmethods when all they really need to do is use python's module-level namespaces better.
I used to work with PHP and recently I was asking myself, whats going on with this classmethod? Python manual is very technical and very short in words so it wont help with understanding that feature. I was googling and googling and I found answer -> http://code.anjanesh.net/2007/12/python-classmethods.html.
If you are lazy to click it. My explanation is shorter and below. :)
in PHP (maybe not all of you know PHP, but this language is so straight forward that everybody should understand what I'm talking about) we have static variables like this:
class A
{
static protected $inner_var = null;
static public function echoInnerVar()
{
echo self::$inner_var."\n";
}
static public function setInnerVar($v)
{
self::$inner_var = $v;
}
}
class B extends A
{
}
A::setInnerVar(10);
B::setInnerVar(20);
A::echoInnerVar();
B::echoInnerVar();
The output will be in both cases 20.
However in python we can add #classmethod decorator and thus it is possible to have output 10 and 20 respectively. Example:
class A(object):
inner_var = 0
#classmethod
def setInnerVar(cls, value):
cls.inner_var = value
#classmethod
def echoInnerVar(cls):
print cls.inner_var
class B(A):
pass
A.setInnerVar(10)
B.setInnerVar(20)
A.echoInnerVar()
B.echoInnerVar()
Smart, ain't?
Class methods provide a "semantic sugar" (don't know if this term is widely used) - or "semantic convenience".
Example: you got a set of classes representing objects. You might want to have the class method all() or find() to write User.all() or User.find(firstname='Guido'). That could be done using module level functions of course...
if you are not a "programmer by training", this should help:
I think I have understood the technical explanations above and elsewhere on the net, but I was always left with a question "Nice, but why do I need it? What is a practical, use case?". and now life gave me a good example that clarified all:
I am using it to control the global-shared variable that is shared among instances of a class instantiated by multi-threading module. in humane language, I am running multiple agents that create examples for deep learning IN PARALLEL. (imagine multiple players playing ATARI game at the same time and each saving the results of their game to one common repository (the SHARED VARIABLE))
I instantiate the players/agents with the following code (in Main/Execution Code):
a3c_workers = [A3C_Worker(self.master_model, self.optimizer, i, self.env_name, self.model_dir) for i in range(multiprocessing.cpu_count())]
it creates as many players as there are processor cores on my comp
A3C_Worker - is a class that defines the agent
a3c_workers - is a list of the instances of that class (i.e. each instance is one player/agent)
now i want to know how many games have been played across all players/agents thus within the A3C_Worker definition I define the variable to be shared across all instances:
class A3C_Worker(threading.Thread):
global_shared_total_episodes_across_all_workers = 0
now as the workers finish their games they increase that count by 1 each for each game finished
at the end of my example generation i was closing the instances but the shared variable had assigned the total number of games played. so when I was re-running it again my initial total number of episodes was that of the previous total. but i needed that count to represent that value for each run individually
to fix that i specified :
class A3C_Worker(threading.Thread):
#classmethod
def reset(cls):
A3C_Worker.global_shared_total_episodes_across_all_workers = 0
than in the execution code i just call:
A3C_Worker.reset()
note that it is a call to the CLASS overall not any INSTANCE of it individually. thus it will set my counter to 0 for every new agent I initiate from now on.
using the usual method definition def play(self):, would require us to reset that counter for each instance individually, which would be more computationally demanding and difficult to track.
What just hit me, coming from Ruby, is that a so-called class method and a so-called instance method is just a function with semantic meaning applied to its first parameter, which is silently passed when the function is called as a method of an object (i.e. obj.meth()).
Normally that object must be an instance but the #classmethod method decorator changes the rules to pass a class. You can call a class method on an instance (it's just a function) - the first argument will be its class.
Because it's just a function, it can only be declared once in any given scope (i.e. class definition). If follows therefore, as a surprise to a Rubyist, that you can't have a class method and an instance method with the same name.
Consider this:
class Foo():
def foo(x):
print(x)
You can call foo on an instance
Foo().foo()
<__main__.Foo instance at 0x7f4dd3e3bc20>
But not on a class:
Foo.foo()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unbound method foo() must be called with Foo instance as first argument (got nothing instead)
Now add #classmethod:
class Foo():
#classmethod
def foo(x):
print(x)
Calling on an instance now passes its class:
Foo().foo()
__main__.Foo
as does calling on a class:
Foo.foo()
__main__.Foo
It's only convention that dictates that we use self for that first argument on an instance method and cls on a class method. I used neither here to illustrate that it's just an argument. In Ruby, self is a keyword.
Contrast with Ruby:
class Foo
def foo()
puts "instance method #{self}"
end
def self.foo()
puts "class method #{self}"
end
end
Foo.foo()
class method Foo
Foo.new.foo()
instance method #<Foo:0x000000020fe018>
The Python class method is just a decorated function and you can use the same techniques to create your own decorators. A decorated method wraps the real method (in the case of #classmethod it passes the additional class argument). The underlying method is still there, hidden but still accessible.
footnote: I wrote this after a name clash between a class and instance method piqued my curiosity. I am far from a Python expert and would like comments if any of this is wrong.
This is an interesting topic. My take on it is that python classmethod operates like a singleton rather than a factory (which returns a produced an instance of a class). The reason it is a singleton is that there is a common object that is produced (the dictionary) but only once for the class but shared by all instances.
To illustrate this here is an example. Note that all instances have a reference to the single dictionary. This is not Factory pattern as I understand it. This is probably very unique to python.
class M():
#classmethod
def m(cls, arg):
print "arg was", getattr(cls, "arg" , None),
cls.arg = arg
print "arg is" , cls.arg
M.m(1) # prints arg was None arg is 1
M.m(2) # prints arg was 1 arg is 2
m1 = M()
m2 = M()
m1.m(3) # prints arg was 2 arg is 3
m2.m(4) # prints arg was 3 arg is 4 << this breaks the factory pattern theory.
M.m(5) # prints arg was 4 arg is 5
I was asking myself the same question few times. And even though the guys here tried hard to explain it, IMHO the best answer (and simplest) answer I have found is the description of the Class method in the Python Documentation.
There is also reference to the Static method. And in case someone already know instance methods (which I assume), this answer might be the final piece to put it all together...
Further and deeper elaboration on this topic can be found also in the documentation:
The standard type hierarchy (scroll down to Instance methods section)
#classmethod can be useful for easily instantiating objects of that class from outside resources. Consider the following:
import settings
class SomeClass:
#classmethod
def from_settings(cls):
return cls(settings=settings)
def __init__(self, settings=None):
if settings is not None:
self.x = settings['x']
self.y = settings['y']
Then in another file:
from some_package import SomeClass
inst = SomeClass.from_settings()
Accessing inst.x will give the same value as settings['x'].
A class defines a set of instances, of course. And the methods of a class work on the individual instances. The class methods (and variables) a place to hang other information that is related to the set of instances over all.
For example if your class defines a the set of students you might want class variables or methods which define things like the set of grade the students can be members of.
You can also use class methods to define tools for working on the entire set. For example Student.all_of_em() might return all the known students. Obviously if your set of instances have more structure than just a set you can provide class methods to know about that structure. Students.all_of_em(grade='juniors')
Techniques like this tend to lead to storing members of the set of instances into data structures that are rooted in class variables. You need to take care to avoid frustrating the garbage collection then.
Classes and Objects concepts are very useful in organizing things. It's true that all the operations that can be done by a method can also be done using a static function.
Just think of a scenario, to build a Students Databases System to maintain student details.
You need to have details about students, teachers and staff. You need to build functions to calculate fees, salary, marks, etc. Fees and marks are only applicable for students, salary is only applicable for staff and teachers. So if you create separate classes for every type of people, the code will be organized.