Inheritance in Python: What's wrong with my code?

Question

Ok so I'm learning inheritance and making instances of another class and I'm having a problem with an error that tells me my ElectricCar class doesn't have a battery attribute. Can someone please point out what I'm missing here? I've been working on this problem for a few days now and I'm at my wit's end.

Here's the error:

Traceback (most recent call last): File "chapt 9 - Classes.py", line 367, in my_tesla.battery.describe_battery() AttributeError: 'ElectricCar' object has no attribute 'battery'

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 = str(self.year) + ' ' + self.make + ' ' + self.model
        return long_name.title()

    def read_odometer(self):
        """Print a statement showing the car's mileage."""    
        print ("This car has " + str(self.odometer_reading) + " miles on it.")

    def update_odometer(self, mileage): 
        """Set the odemeter 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 odemeter")

    def increment_odometer(self, miles):
        self.odometer_reading += miles

class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery_size = Battery()

    def describe_battery(self):
        print ("This car has a " + str(self.battery_size) + "-kWh battery.")

    def fill_gas_tank():
        print ("This car doesn't need a gas tank!")


class Battery():
    def __init__(self, battery_size=70):
        self.battery_size = battery_size

    def describe_battery(self):
        print ("This car has a " + str(self.battery_size) + "-kWh battery.")

    def get_range(self):
        """Print a statement about the range this battery provides."""
        if self.battery_size == 70:
            range = 240
        elif self.battery_size == 85:
            range = 270

    message = "This car can go approximately " + str(range)
    message += " miles on a full charge."
    print (message)


def upgrade_battery(self):
    if self.battery_size == 85:
        self.battery_size = 85
        print ("\nYour battery size is: " + self.battery_size + "  You don't need an upgrade.")
    else:
        self.battery_size = 85
        print ("\nYour battery size has been upgraded to: " + str(self.battery_size))

my_tesla = ElectricCar('tesla', 'model s', 2016)
print (my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()     
my_tesla.battery.get_range()    

Answer 1

The problem is that in your ElectricCar class, you're initializing the Battery class and setting it to the variable self.battery_size instead of self.battery .

Changing your code to:

class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery = Battery()  # NOT self.battery_size

should make it work.