David Agabi David Agabi - 4 months ago 9
Python Question

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

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

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.