A class is an object that can be used to store data or do a thing.
class Dog:
"""A simple attempt to model a dog."""
def __init__(self, name, age):
"""Initialize name and age attributes."""
self.name = name
self.age = age
def sit(self):
"""Simulate a dog sitting in response to a command."""
print(f"{self.name} is now sitting.")
def roll_over(self):
"""Simulate rolling over in response to a command."""
print(f"{self.name} rolled over!")
Convention is to capitalize Names that refer to classes.
The init() Method #
A function that’s part of a class is a method. The init() method is a special method that Python runs automatically whenever a new instance is created based on the class.
Classes always pass the self parameter which is just a reference to the class itself with any attributes and methods in the class.
Making an Instance of a Class #
A class is just a set of instructions for how to make an instance.
my_dog = Dog('Willie', 6)
print(f"My dog's name is {my_dog.name}.")
print(f"My dog is {my_dog.age} years old.")
My dog's name is Willie.
My dog is 6 years old.
This creates an instance of Dog and using dot notation prints the values for self.name and self.age from that class.
Calling Methods #
class Dog:
--snip--
my_dog = Dog('Willie', 6)
my_dog.sit()
my_dog.roll_over()
Methods from a class are called with dot notation.
Willie is now sitting.
Willie rolled over!
Creating Multiple Instances #
You can create as many instances from a class as you need.
class Dog:
--snip--
my_dog = Dog('Willie', 6)
your_dog = Dog('Lucy', 3)
print(f"My dog's name is {my_dog.name}.")
print(f"My dog is {my_dog.age} years old.")
my_dog.sit()
print(f"\nYour dog's name is {your_dog.name}.")
print(f"Your dog is {your_dog.age} years old.")
your_dog.sit()
My dog's name is Willie.
My dog is 6 years old.
Willie is now sitting.
Your dog's name is Lucy.
Your dog is 3 years old.
Lucy is now sitting.
Working with Classes and Instances #
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
def get_descriptive_name(self):
"""Return a neatly formatted descriptive name."""
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
2019 Audi A4
Setting a Default Value for an Attribute #
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.")
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.read_odometer()
Note, this sets the odometer_reading attribute to a default value of 0.
2019 Audi A4
This car has 0 miles on it.
Modifying Attribute Values #
Three methods:
- Change value through an instance
- Set value through a method
- Increment value through a method
Modify attribute directly through an instance #
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.")
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.odometer_reading = 23
my_new_car.read_odometer()
2019 Audi A4
This car has 23 miles on it.
Define a method that updates attributes #
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."""
self.odometer_reading = mileage
my_new_car = Car('audi', 'a4', 2019)
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(23)
my_new_car.read_odometer()
Note, we added the update_odometer method to the class.
2019 Audi A4
This car has 23 miles on it.
Define a method that increments an attribute’s value #
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
my_used_car = Car('subaru', 'outback', 2015)
print(my_used_car.get_descriptive_name())
my_used_car.update_odometer(23_500)
my_used_car.read_odometer()
my_used_car.increment_odometer(100)
my_used_car.read_odometer()
Note, we’ve added the increment_odometer method.
2015 Subaru Outback
This car has 23500 miles on it.
This car has 23600 miles on it.