EDIT2: Thank you all for your help! EDIT: on adding @staticmethod, it works. However I am still wondering why i am getting a type error here.
I have just started OOPS a
disclaimer: this is not a just to the point answer, it's more like a piece of advice, even if the answer can be found on the references
IMHO: object oriented programming in Python sucks quite a lot.
The method dispatching is not very straightforward, you need to know about bound/unbound instance/class (and static!) methods; you can have multiple inheritance and need to deal with legacy and new style classes (yours was old style) and know how the MRO works, properties...
In brief: too complex, with lots of things happening under the hood. Let me even say, it is unpythonic, as there are many different ways to achieve the same things.
My advice: use OOP only when it's really useful. Usually this means writing classes that implement well known protocols and integrate seamlessly with the rest of the system. Do not create lots of classes just for the sake of writing object oriented code.
Take a good read to this pages:
you'll find them quite useful.
If you really want to learn OOP, I'd suggest starting with a more conventional language, like Java. It's not half as fun as Python, but it's more predictable.