Correct way of returning new class object (which could also be extended)

April 16, 2022

I am trying to find a good way for returning a (new) class object in class method that can be extended as well.

I have a class (classA) which has among other methods, a method that returns a new classA object after some processing

class classA:
   def __init__(): ...

   def methodX(self, **kwargs):
      process data
      return classA(new params)

Now, I am extending this class to another classB. I need methodX to do the same, but return classB this time, instead of classA

class classB(classA):
   def __init__(self, params):
      super().__init__(params)
      self.newParams = XYZ
   
   def methodX(self, **kwargs):
      ???

This may be something trivial but I simply cannot figure it out. In the end I dont want to rewrite the methodX each time the class gets extended.

Thank you for your time.

>Solution :

Use the __class__ attribute like this:

class A:
    def __init__(self, **kwargs):
        self.kwargs = kwargs

    def methodX(self, **kwargs):
        #do stuff with kwargs
        return self.__class__(**kwargs)

    def __repr__(self):
        return f'{self.__class__}({self.kwargs})'

class B(A):
    pass

a = A(foo='bar')
ax = a.methodX(gee='whiz')
b = B(yee='haw')
bx = b.methodX(cool='beans')

print(a)
print(ax)
print(b)
print(bx)