catalogue
9.1 creating and using classes
9.1.2 create instances based on classes
9.2.2 assigning default values to attributes
9.2.3 modifying attribute values
9.3.2 define attributes and methods for subclasses
9.3.3 method of overriding parent class
9.3.4 using instances as attributes
9.4.1 importing a single class
9.4.2 storing multiple classes in one module
9.4.3 importing multiple classes from a module
9.4.5 import all classes in the module
9.4.6 importing one module into another
Chapter 9 class
9.1 creating and using classes
9.1.1 create Dog class
class Dog:
"""A simple attempt to simulate a dog."""
def __init__(self, name, age):
"""Initialize properties name and age. """
self.name = name
self.age = age
def sit(self):
"""Simulate a dog squatting when ordered."""
print(f"{self.name} is now sitting.")
def roll_over(self):
"""Simulate a dog rolling when ordered."""
print(f"{self.name} rolled over!")9.1.2 create instances based on classes
class Dog:
"""A simple attempt to simulate a puppy."""
def __init__(self, name, age):
"""Initialize properties name and age. """
self.name = name
self.age = age
def sit(self):
"""Simulate a dog squatting when ordered."""
print(f"{self.name} is now sitting.")
def roll_over(self):
"""Simulate a dog rolling when ordered."""
print(f"{self.name} rolled over!")
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.
my_dog = Dog('Willie', 6)
my_dog.sit()
my_dog.roll_over()Willie is now sitting. Willie rolled over!
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.
9.2 use classes and instances
9.2.1 Car
class Car:
"""A simple attempt to simulate a car."""
def __init__(self, make, model, year):
"""Initialize the properties that describe the car."""
self.make = make
self.model = model
self.year = year
def get_descriptive_name(self):
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
9.2.2 assigning default values to attributes
class Car:
"""A simple attempt to simulate a car."""
def __init__(self, make, model, year):
"""Initialize the properties that describe the car."""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
"""Print a message indicating the mileage of the car."""
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()2019 Audi A4 This car has 0 miles on it.
9.2.3 modifying attribute values
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.
class Car:
"""A simple attempt to simulate a car."""
def __init__(self, make, model, year):
"""Initialize the properties that describe the car."""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
"""Print a message indicating the mileage of the car."""
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""Set the odometer reading to the specified 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()2019 Audi A4 This car has 23 miles on it.
def update_odometer(self, mileage):
"""
Set the odometer reading to the specified value.
It is forbidden to callback the odometer reading.
"""
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print('You can\'t roll back an odometer!')class Car:
"""A simple attempt to simulate a car."""
def __init__(self, make, model, year):
"""Initialize the properties that describe the car."""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
"""Print a message indicating the mileage of the car."""
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""
Set the odometer reading to the specified value.
It is forbidden to callback the odometer reading.
"""
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print('You can\'t roll back an odometer!')
def increment_odometer(self, miles):
"""Increase the odometer reading by the specified amount."""
self.odometer_reading += miles
my_new_car = Car('audi', 'a4', '2019')
print(my_new_car.get_descriptive_name())
my_new_car.update_odometer(23_500)
my_new_car.read_odometer()
my_new_car.increment_odometer(100)
my_new_car.read_odometer()2019 Audi A4 This car has 23500 miles on it. This car has 23600 miles on it.
9.3 succession
When a class inherits from another class, it will automatically get all the properties and methods of the other class. The original class is called the parent class, while the new class is called the child class. Subclasses inherit all the properties and methods of the parent class, and can also define their own properties and methods.
class ElectricCar(Car):
"""The uniqueness of electric vehicles."""
def __init__(self, make, model, year):
"""Initializes the properties 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
9.3.2 define attributes and methods for subclasses
class ElectricCar(Car):
"""The uniqueness of electric vehicles."""
def __init__(self, make, model, year):
"""Initializes the properties of the parent class."""
super().__init__(make, model, year)
self.battery_size = 75
def describe_battery(self):
"""Print a message describing the battery capacity."""
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.
9.3.3 method of overriding parent class
def fill_gas_tank(self):
"""Electric cars have no fuel tanks."""
print("This car doesn't need a gas tank!")9.3.4 using instances as attributes
class Car:
"""A simple attempt to simulate a car."""
def __init__(self, make, model, year):
"""Initialize the properties that describe the car."""
self.make = make
self.model = model
self.year = year
self.odometer_reading = 0
def get_descriptive_name(self):
long_name = f"{self.year} {self.make} {self.model}"
return long_name.title()
def read_odometer(self):
"""Print a message indicating the mileage of the car."""
print(f"This car has {self.odometer_reading} miles on it.")
def update_odometer(self, mileage):
"""
Set the odometer reading to the specified value.
It is forbidden to callback the odometer reading.
"""
if mileage >= self.odometer_reading:
self.odometer_reading = mileage
else:
print('You can\'t roll back an odometer!')
def increment_odometer(self, miles):
"""Increase the odometer reading by the specified amount."""
self.odometer_reading += miles
class Battery:
"""A simple attempt to simulate electric vehicle battery."""
def __init__(self, battery_size=75):
"""Initialize battery properties."""
self.battery_size = battery_size
def describe_battery(self):
"""Print a message describing the battery capacity."""
print(f"This car has a {self.battery_size}-kWh battery.")
class ElectricCar(Car):
"""The uniqueness of electric vehicles."""
def __init__(self, make, model, year):
"""Initializes the properties of the parent class."""
super().__init__(make, model, year)
self.battery = Battery()
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()2019 Tesla Model S This car has a 75-kWh battery.
class Battery:
"""A simple attempt to simulate electric vehicle battery."""
def __init__(self, battery_size=75):
"""Initialize battery properties."""
self.battery_size = battery_size
def describe_battery(self):
"""Print a message describing the battery capacity."""
print(f"This car has a {self.battery_size}-kWh battery.")
def get_range(self):
"""Print a message indicating the battery range."""
if self.battery_size == 75:
range = 260
elif self.battery_size == 100:
range = 315
print(f"This car can go about {range} miles on a full charge.")2019 Tesla Model S This car has a 75-kWh battery. This car can go about 260 miles on a full charge.
9.3.5 simulated object
There is no right or wrong in the modeling methods of the real world. Some methods are more efficient, but it needs some practice to find the most efficient representation.
9.4 import class
9.4.1 importing a single class
from car import Car
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.
9.4.2 storing multiple classes in one module
from car import ElectricCar
my_tesla = ElectricCar('tesla', 'model s', 2019)
print(my_tesla.get_descriptive_name())
my_tesla.battery.describe_battery()
my_tesla.battery.get_range()2019 Tesla Model S This car has a 75-kWh battery. This car can go about 260 miles on a full charge.
9.4.3 importing multiple classes from a module
from car import Car, ElectricCar
my_beetle = Car('volkswagen', 'beetle', '2019')
print(my_beetle.get_descriptive_name())
my_tesla = ElectricCar('tesla', 'roadster', '2019')
print(my_tesla.get_descriptive_name())2019 Volkswagen Beetle 2019 Tesla Roadster
9.4.4 import the whole module
import car
my_beetle = car.Car('volkswagen', 'beetle', '2019')
print(my_beetle.get_descriptive_name())
my_tesla = car.ElectricCar('tesla', 'roadster', '2019')
print(my_tesla.get_descriptive_name())2019 Volkswagen Beetle 2019 Tesla Roadster
9.4.5 import all classes in the module
from module_name import *
9.4.6 importing one module into another
from car import Car
from electric_car import ElectricCar
my_beetle = Car('volkswagen', 'beetle', 2019)
print(my_beetle.get_descriptive_name())
my_tesla = ElectricCar('tesla', 'roadster', 2019)
print(my_tesla.get_descriptive_name())2019 Volkswagen Beetle 2019 Tesla Roadster
9.4.7 using aliases
from car import Car
from electric_car import ElectricCar as EC
my_beetle = Car('volkswagen', 'beetle', 2019)
print(my_beetle.get_descriptive_name())
my_tesla = EC('tesla', 'roadster', 2019)
print(my_tesla.get_descriptive_name())2019 Volkswagen Beetle 2019 Tesla Roadster
9.4.8 custom workflow
Start by making the code structure as simple as possible. Make sure that all the work can be completed in a separate class as soon as possible.
9.5 Python standard library
The Python standard library is a set of modules, which are included in the Python we install.
from random import randint print(randint(1, 6))
4
from random import choice players = ['charles', 'martina', 'michael', 'florence', 'eli'] first_up = choice(players) print(first_up)
florence
Class 9.6 coding style
The class name shall adopt hump naming method, that is, the first letter of each word in the class name shall be capitalized without underline. The instance name and module name are in lowercase and underlined between words.