Python basic inheritance [duplicate]

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Understanding Python super() with __init__() methods [duplicate] (7 answers)

Closed 10 years ago.

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

?

Answer 1

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

• Kevin: Prefer using super() if possible.
• Daniel: Why is supper a prefer approach? When i was learning about it they kept using this approach.
• Kevin: It plays nicer with multiple inheritance.
• Daniel: Gotcha! I didn't know about it. thanks for the link

Answer 2

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, ...)
 pass

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.

Answer 3

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.