How to access class method and class variable from a class to another class's instance method in Python?

Question

Imagine I have three classes as shown in the code snippet.

In class A, I have class variable and class method that I would like to access in class C after multiple inheritance, i.e., C(A,B) where B is just another class. I have found that I can access both class method and variable via self., super(). or by using the class name it self, i.e., A.

The question is, what could be the advised way to access, if any. Or, all three are equally fine? Thanks in advance. Regards, DS

class A():
    school='XYZ'
    def __init__(self):
        print('in init A')
    def feature1(self):
        print('Feature1-A working')
    def feature2(self):
        print('Feature2-A working')

    @classmethod
    def show_avg(cls,m1,m2,m3):
        return (m1+m2+m3)/3
    @classmethod
    def info(cls):
        return cls.school

class B():
    def __init__(self):
        print('in init B')
    def feature3(self):
        print('Feature1-B working')
    def feature4(self):
        print('Feature2-B working')

class C(A,B):
    def __init__(self):
        super().__init__()
        print('in init C') 
    def get_avg_from_super_class(self):
        avg1=self.show_avg(2,3,4)
        avg2=super().show_avg(2,3,4)
        avg3=A.show_avg(2,3,4)
        print('avg by calling self:{}, avg by calling super():{}, avg by alling class name:{}'.format(avg1,avg2,avg3))
    def get_info(self):
        print (A.info())
        print(self.info())
        print(super().info())

ywbaek · Accepted Answer · 2020-03-30 19:13:10Z

1

For your code, either of the three way works fine.
But in general, I would say using the class name to access class methods and class variables is the safest way to ensure you are accessing the right methods/variables.

For example,

1.If you have another info() in class C whether it's a class method or an instance method,

self.info()

will call that method defined in class C, NOT the one in class A

2.If the order of inheritance is different as to class C(B, A), and you have another info() in class B whether it's a class method or an instance method,

super().info()

will call that method defined in class B, NOT the one in class A

answered Mar 30, 2020 at 19:13

ywbaek

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4 Comments

Debashish Saha Over a year ago

Perhaps a correction needed? If one creates an object from class C and tries to access instance method from super class A, then accessing by class name does not work. It has to be self. Am I right?

ywbaek Over a year ago

@DebashishSaha You actually CAN access instance method by class name, but you won't be using it as "instance method", meaning you have to actually pass in an argument at self position.

Debashish Saha Over a year ago

Thanks. It works. Could you then please explain a bit why one should pass self as an argument to the method inherited from super class given the fact that super().__init__() is already there?

ywbaek Over a year ago

@DebashishSaha, When overriding the method? And also, in the method definition? or when the method is invoked?

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