Chapter 9: Classes

Classes

In object-oriented programming you write classes that represent real-world things and situations, and you create objects based on these classes.

Making an object from a class is called instantiation, and you work with instances of a class.

Styling classes

Class names should be written in CamelCase, no underscores  
Every class should have a docstring immediately following the class definition  
Every module should have a docstring to describe the function

Creating and Using a Class

Example a Dog Class

class Dog:
    """ A model of a dog """
    def __init__(self, name, age):
        """ Inialize name and age attributes """
        self.name = name
        self.age = age

    def sit(self):
        """ Stimulate a dog sitting command """
        print(f"{self.name} is now sitting.")

    def roll_over(self):
        """ Stimulate a dog rolling over command """
        print(f"{self.name} rolled over!")

The init() method

A function that's part of a class is a method.
A special method that python runs automatically whenever we create a new instance based on the class.

The self parameter

The self parameter is required in the method definition, and it must come first before the other parameters. Self must be include, as Python passes the self argument.

How to use the instance

When we call the dog instance for example, we don't need to call self.
We call upon all the other arguments.

import dog

my_dog = dog.Dog('Willie', '6')

print(my_dog.name, my_dog.age)
my_dog.sit()

Inheritance

class Dog:
    """ A model of a dog """
    def __init__(self, name, age):
        """ Inialize name and age attributes """
        self.name = name
        self.age = age

    def sit(self):
        """ Stimulate a dog sitting command """
        print(f"{self.name} is now sitting.")

    def roll_over(self):
        """ Stimulate a dog rolling over command """
        print(f"{self.name} rolled over!")



class puppy(Dog):
    def __init__(self, name, age):
        super().__init__(name, age)

    def get_desc(self):
        return f"{self.name} is {self.age} years old!"
my_dog = puppy('Paw', '1')
print(my_dog.get_desc())

Overriding

class Dog:
    """ A model of a dog """
    def __init__(self, name, age):
        """ Inialize name and age attributes """
        self.name = name
        self.age = age

    def sit(self):
        """ Stimulate a dog sitting command """
        print(f"{self.name} is now sitting.")

    def roll_over(self):
        """ Stimulate a dog rolling over command """
        print(f"{self.name} rolled over!")



class puppy(Dog):
    def __init__(self, name, age):
        super().__init__(name, age)

    def get_desc(self):
        return f"{self.name} is {self.age} years old!"

    def sit(self):
        return f"{self.name} didn't sit"
my_dog = puppy('Paw', '1')
print(my_dog.sit())

Aliases

We can the change the names of modules to better organized and reduce the length of text.

from eletric_car import ElectricCar as EC
my_telsa = EC('telsa', 'roadstar', 2019)