Concept of Object Oriented Programs in Python

class A:
     def __init__(self):
         self.__i = 1
         self.j = 5
 
     def display(self):
         print(self.__i, self.j)
class B(A):
     def __init__(self):
         super().__init__()
         self.__i = 2
         self.j = 7  
c = B()
c.display()

class Demo:
    def check(self):
        return " Demo's check "  
    def display(self):
        print(self.check())
class Demo_Derived(Demo):
    def check(self):
        return " Derived's check "
Demo().display()
Demo_Derived().display()

class A:
    def __repr__(self):
        return "1"
class B(A):
    def __repr__(self):
        return "2"
class C(B):
    def __repr__(self):
        return "3"
o1 = A()
o2 = B()
o3 = C()
print(obj1, obj2, obj3)

class A():
    pass
class B(A):
    pass
class C(B):
    pass

class Demo:
    def __init__(self):
        self.a = 1
        self.__b = 1
 
    def display(self):
        return self.__b
 
obj = Demo()
print(obj.__b)