Python Forum

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...

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:

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().