Python basic inheritance

Question

I am having difficulties understanig inheritance in Python, but I have an idea how it works because of my somewhat larger experience in Java... To be clear, I searched the questiones here as well as online documentation, so I am aware this will be branded as repeated question in an instant :P

My code on Codecademy passes like this:

class Car(object):
    condition = "new"
    def __init__(self, model, color, mpg):
        self.model = model
        self.color = color
        self.mpg   = mpg

    def display_car(self):
        return "This is a %s %s with %s MPG." % (self.color, self.model, self.mpg)

    def drive_car(self):
        self.condition = "used"

class ElectricCar(Car):
    def __init__(self, model, color, mpg, battery_type):
        self.model = model
        self.color = color
        self.mpg   = mpg
        self.battery_type = battery_type

But as far as I can see, I'm almost defining a new class... Where is the inheritance in that? Could I do something like:

class ElectricCar(Car):
    def __init__(self, battery_type):
        self.model = model
        self.color = color
        self.mpg   = mpg
        self.battery_type = battery_type

Maybe something with a keyword

super

?

Daniel · Answer 1 · 2015-03-20T16:08:46.730

6

You can call the Car init method and pass its arguments

class ElectricCar(Car):
    def __init__(self, model, color, mpg, battery_type):
        Car.__init__(self,model,color,mpg)
        self.battery_type = battery_type

Or you can also use the super method which is a preferred approach as mentioned in the comments.

class ElectricCar(Car):
    def __init__(self, model, color, mpg, battery_type):
        super(ElectricCar,self).__init__(model, color, mpg)
        self.battery_type = battery_type

edited Mar 20 '15 at 16:08

answered Mar 20 '15 at 15:55

Daniel

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2

Prefer using `super()` if possible. – Kevin Mar 20 '15 at 15:57
1

Why is supper a prefer approach? When i was learning about it they kept using this approach. – Daniel Mar 20 '15 at 15:58
1

It [plays nicer with multiple inheritance](https://rhettinger.wordpress.com/2011/05/26/super-considered-super/). – Kevin Mar 20 '15 at 15:59
Gotcha! I didn't know about it. thanks for the link – Daniel Mar 20 '15 at 16:00

score 1 · Answer 2 · answered Mar 20 '15 at 15:58

If you're just inheriting the object class, you are correct in saying you are essentially creating a new class - it just provides a base. In fact, in Python 3.X, this isn't needed at all. Define a class like

class Car:
    def __init(self, ...

and the object inheritance goes without saying.

You're on the right track for using it. The real power of inheritance is in building off other predefined classes, such as your ElectricCar inheriting from Car, through a definition such as:

class ElectricCar(Car):
    super(ElectricCar, self).__init__()
    ...

This gives you the functionality of the Car class without having to redefine everything.

Check out the docs on inheritance here for more detailed info.

score 0 · Answer 3 · answered Mar 20 '15 at 15:55

Where is the inheritance in that?

The inheritance lies in what you can do with these classes:

>>> car = Car('Ford Prefect', 'white', 42)
>>> print(car.display_car())
This is a white Ford Prefect with 42 MPG.
>>> electric_car = ElectricCar('Tesla Model S', 'silver', None, 'lead-acid')
>>> print(electric_car.display_car())
This is a silver Tesla Model S with None MPG.

Notice that you didn't have to write the ElectricCar.display_car() method.

Python basic inheritance

3 Answers3