error in constructor overriding in python3

[srm]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

class Baseclass1:     def __init__(self,x,y):        self.x=x        self.y=y        print(self.x+self.y) class Derived(Baseclass1):             def cmethod(self):                   Baseclass1.__init__(self,x,y)#Base constructor called with class name         print(self.x * self.y)               ob=Derived(4,5) ob.cmethod()

Error:
Traceback (most recent call last):
  File "C:/Python37/understandingConstructor.py", line 33, in <module>
    ob.cmethod()
  File "C:/Python37/understandingConstructor.py", line 29, in cmethod
    Baseclass1.__init__(self,x,y)#Base constructor called with class name
NameError: name 'x' is not defined

here I am not able to override construcor of the base class and getting error.probably my code is wrong...but can anyone explain how constructor overriding code in python with proper example...

[ichabod801]

First of all, the error has nothing to do with overriding. The error is because x and y are not defined in cmethod. The only place they are defined is in BaseClass1.__init__, where they are defined as parameters. If you want to access the instance values of x and y from within cmethod, you need to use self.x and self.y, as you did in BaseClass1.__init__.

Second of all, you are not overriding anything. When you override a method, it has the same name. That makes the overridden version be called for the derived class. It would be more like this:

1 2 3 4 5 6 7 8 9

class Plus(object):     def __init__(self, x, y):         self.x = x         self.y = y     def act(self):         return x + y class Minus(Plus):     def act(self)         return x - y

Output:
>>> p = Plus(8, 1)
>>> m = Minus(8, 1)
>>> p.act()
9
>>> m.act()
7

When the Minus instance m is created, it uses the derivied __init__ method to assign x and y. But when m.act is called, it uses the overridden act method to subtract instead of adding.

So you example is a bit odd. By the time you call Derived.cmethod, the instance has already been initialized using the __init__ method inherited from BaseClass1. So it's not clear why you would call __init__ again. Also, if you are in an overridden method, and you want to call the parent class's method, you generally use super().