Sometimes it’s useful to have a class which is a specialized version of another class. To do this, you can use inheritance. In this case the child class will inherit attributes and methods from the parent class.
Inheritance #
To inherit things from the parent class call the __init__() method from the
parent class. Call your parent.
class Car:
"""A simple attempt to represent a car."""
def __init__(self, make, model, year):
"""Initialize attributes to describe a car."""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
"""Return a neatly formatted descriptive name."""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
"""Print a statement showing the car's mileage."""
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""
Set the odometer reading to the given value.
Reject the change if it attempts to roll the odometer back.
"""
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print("You can't roll back an odometer!")
def increment_odometer(self, miles):
"""Add the given amount to the odometer reading."""
self.odometer_reading += miles
class ElectricCar(Car):
"""Represent aspects of a car, specific to electric vehicles."""
def __init__(self, make, model, year):
"""Initialize attributes of the parent class."""
super().__init__(make, model, year)
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
2019 Tesla Model S
Note, using the super() function comes from the convention of calling the
parent class a superclass and the child class a subclass.
Defining Attributes and Methods for the Child Class #
class Car:
-- snip --
class ElectricCar(Car):
"""Represent aspects of a car, specific to electric vehicles."""
def __init__(self, make, model, year):
"""
Initialize attributes of the parent class.
Then initialize attributes specific to an electric car.
"""
super().__init__(make, model, year)
self.battery_size = 75
def describe_battery(self):
"""Print a statement describing the battery size."""
print(f"This car has a {self.battery_size}-kWh battery.")
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
my_tesla.describe_battery()
2019 Tesla Model S
This car has a 75-kWh battery.
Overriding Methods from the Parent Class #
You can override a method from the parent class by just using the same name as the one in the parent class. Python will use the method in the child class instead of the one in the parent if they’re the same name.
Instances as Attributes #
It may make sense to split a class into multiple classes if it’s getting too long. In the example above we might split the stuff about batteries into it’s own class.
class Car:
-- snip --
class Battery:
"""A simple attempt to model a battery for an electric car."""
def __init__(self, battery_size=75):
"""Initialize the battery's attributes."""
self.battery_size = battery_size
def describe_battery(self):
"""Print a statement describing the battery size."""
print(f"This car has a {self.battery_size}-kWh battery.")
class ElectricCar(Car):
"""Represent aspects of a car, specific to electric vehicles."""
def __init__(self, make, model, year):
"""
Initialize attributes of the parent class.
Then initialize attributes specific to an electric car.
"""
super().__init__(make, model, year)
self.battery_size = Battery()
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()