Python - how to correctly set up hierarchy of classes?

Question

I have the following code:

class Computer(object):
    def __init__(self, name):
        self.name = name

class CPU(Computer):
    def __init__(self):
        super(CPU, self).__init__(name)
        self.name = name

mycomputer = Computer('My Computer')
mycomputer.CPU.name = 'Intel'

print mycomputer.name, mycomputer.CPU.name

I would like to get the following:

My Computer, Intel

But I'm getting the following error:

AttributeError: 'Computer' object has no attribute 'CPU'    

How do I set up the class correctly, so once I run the main code, I would get what I need? I'm not even sure if I'm using super() correctly at all.

I really appreciate all your help.

Answer 1

The semantical problem in the hierarchy you built is the fact that CPU is actually not a computer type, it is a part of computer, so you should have defined it as an attribute instead of a sub type:

class Computer(object):
    def __init__(self, name, cpu):
        self.name = name
        self.cpu = cpu

Classes that are hierarchically related should have something in common even if they represent different things and have unique attributes that help us identify them. For instance; a car is a vehicle, a truck is also a vehicle so that vehicle can be defined as super class of both car and truck. Although they look totally different, they have something in common as vehicles: engine, wheel, transmission etc.

Getting back to you question, a CPU is basically a heart of computer, a required thing for all type of computers so it should be something that is inherited from super class Computer:

class Computer(object):
    def __init__(self, name, cpu):
        self.name = name
        self.cpu = cpu

class Laptop(Computer):
    def __init__(self, name, cpu, manufacturer):
        super(Laptop, self).__init__(name, cpu)
        self.manufacturer = manufacturer

class AutomatedTellerMachine(Computer):
    def __init__(self, name, cpu, bank):
        super(AutomatedTellerMachine, self).__init__(name, cpu)
        self.bank = bank

---

>>> macbook = Laptop('My Macbook', 'Intel', 'Apple')
>>> atm = AutomatedTellerMachine('ATM 1', 'AMD', 'Wells Fargo')

There is a good read about class inheritance in Python. I'd strongly recommend to read it once.

Answer 2

I don't think you want subclassing at all.

class Computer(object):
    def __init__(self, name, cpu):
        self.name = name
        self.cpu = cpu

class CPU(object):
    def __init__(self, manufacturer):
        self.manufacturer = manufacturer

intel_cpu = CPU('Intel')
mycomputer = Computer('My Computer', intel_cpu)

print "{}, {}".format(mycomputer.name, mycomputer.cpu.manufacturer)

Gives this output:

My Computer, Intel