Inheriting from super class to subclasses in Python

Question

I have a super class which has some class attributes like:

class Config(object):    
    LENGTH = 1
    BREADTH = 3

Now ,I have created a subclass which will override the parent class attributes.

 class Sub1(Config):
     def __init__():
        self.LENGTH = 200
        self.BREADTH = 100
        self.AREA = self.LENGTH * self.BREADTH

Now I need to write another subclass which will overwrite the values of the first sub class. Here, shall I inherit from the parent class Config or I can overwrite the values in the subclass itself and change it.

class Sub2(Sub1):
   self.AREA_UPDATED = self.AREA + 20

This is not working.

class Sub2(Config):
    self.LENGTH = "efg"
    self.BREADTH = 100
    self.AREA = self.LENGTH * self.BREADTH
    self.AREA_UPDATED = self.AREA + 20

This works. What am I doing conceptually wrong, is it that the parent class can be inherited only? Kindly advice.

Thanks

Attila Bognár · Accepted Answer · 2018-12-18 07:09:48Z

3

You can't use self in the class scope. You should just use the variable name simply like this:

class Sub2(Config):
    LENGTH = "efg"
    BREADTH = 100
    AREA = LENGTH * BREADTH
    AREA_UPDATED = AREA + 20

Because this way you will overwrite the class attributes not just the instance attributes as you did it in the __init__.

Inheriting from Sub1 you can do the same:

class Sub1(Config):
    LENGTH = 200
    BREADTH = 100
    AREA = LENGTH * BREADTH 

class Sub2(Sub1):
    AREA_UPDATED = Sub1.AREA + 20

edited Dec 18, 2018 at 7:09

answered Dec 18, 2018 at 6:57

Attila Bognár

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function · Accepted Answer · 2018-12-18 07:45:39Z

0

Change

class Sub2(Sub1):
   self.AREA_UPDATED = self.AREA + 20

to

class Sub2(Sub1):
  def __init__(self):
     self.AREA_UPDATED = self.AREA + 20

edited Dec 18, 2018 at 7:45

answered Dec 18, 2018 at 6:54

function

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1 Comment

Attila Bognár Over a year ago

You should fix the __init__ like this: def __init__(self):. And on the class level you can't use self.

capo · Accepted Answer · 2018-12-18 07:59:11Z

Correct me if I'm wrong, but wouldn't you use the breadth and width in the init to instantiate an object correctly? I mean just like this:

class Config(object):
   def __init__(self, width, breadth):
       self.width = width
       self.breadth = breadth
       self.area = width*breadth

taking the config as a superclass ( you could also use it as abstract base class, in which case my solution would be wrong).

And afterwards just properly let Sub1 inherit from Config like this:

class Sub1(Config):
  def __init__(self,width,breadth):
      Config.__init__(self,width,breadth)
      self.area = width * breadth

for sub2 you could obviously do the same. If you would want to know the updated area, you could just use setters for the attributes the class has.

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