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09 Python OOP

Object Oriented programming (OOP) is a method of structuring a program by bundling related properties and behaviors into individual objects.

9.1 4 principles of OOP

There are 4 major principles that make an language Object Oriented. These are Encapsulation, Data Abstraction, Polymorphism and Inheritance. These are also called as four pillars of Object Oriented Programming.

4 principles

9.1.1 Encapsulation

Encapsulation is achieved when each object keeps its state private, inside a class. Other objects don’t have direct access to this state. Instead, they can only call a list of public functions — called methods.

9.1.2 Abstraction

Data Abstraction is a way of creating a simple model of a more complex real-world entities, which contains the only important properties from the perspective of the context of an application.

Data Abstraction

OOP Abstraction is using abstract class/Interface we express the intent of the class rather than the actual implementation.

Abstraction

https://learntocodetogether.com/what-the-heck-is-oop/

9.1.4 Inheritance

In OOP, the child class could reuse all method of parents class.(Except the private members in some advance language).

All child is a type of parents. for example, car is type of vehicle, bird is type of animal, chicken is type of bird, etc.

Inheritance

9.1.3 Polymorphism

Polymorphism is mean each child class could have different behaver through inheritance same method from parents.

Polymorphism

class Animal(object):
    def __init__(self, name):
        self.name = name

    def talk(self):
        raise NotImplementedError


class Dog(Animal):
    def talk(self):
        return "Bow...Bow..."


class Cat(Animal):
    def talk(self):
        return "Meow...Meow..."


class Human(Animal):
    def talk(self):
        return "I can talk more...."

9.2 Example of OOP in Python

9.2.1 Animal example 1

Below example show the Animal dog, and turtle class in OOP.

example1

class Animal:

    def __init__(self, name):
        self.name = name 
        print(self.name + " was adopted.")

    def run(self):
        print("running!")

class Dog(Animal):

    def __init__(self, name):
        self.name = name 
        print(self.name + " was adopted.")

    def bark(self):
        print("woof!")

class Turtle(Animal):

    def __init__(self):
        super().init 

    def run(self):
        print("running slowly!")

# we don't care how it works just bark
spot = Dog("spot") #=> spot was adopted. 
spot.bark() #=> woof! 

# Dog inheritance the run method from animal
spot.run() #=> running! 

# we get back an interesting response 
tim = Turtle("tim") #=> tim was adopted. 
tim.run() #=> running slowly!

9.2.2 Animal example 2

Below show more complex example of Inheritance and Polymorphism. understand inheritance

class Animal:
    def __init__(self,name,gender):
        self.name=name
        self.gender=gender
    def __str__(self) -> str:
        return "class={}: name:{} gender:{}".format(type(self).__name__,self.name,self.gender)

class Bird(Animal):
    def __init__(self,name,gender):
        Animal.__init__(self,name,gender)
    def flying(self):
        return "birds flying..."  

class Chicken(Bird):
    def __init__(self,name,gender):
        super().__init__(name,gender) #python 3 and upper you could use supper() to init parent without self
        self.gender=gender
    def flying(self):
        return "chicken {} can't fly..".format(self.name)

class CanadianGoose(Bird):
    def __init__(self,name,gender):
        Bird.__init__(self,name,gender)
    def swimming(self):
        return "Canadian Goose floating on the water.."

aHen = Chicken("egg hatcher","F")
aRooster = Chicken("big Foot","M")
aGoose = CanadianGoose("wild goose","unknown") 

print(aHen.flying())
print(aGoose.flying())
print(aGoose.swimming())
print(aRooster)

9.3 Home work

Please practice the OOP by write class vehicle, Car, truck.

9.4 Reference

Read more if you need understand more of the OOP for python