Object-oriented programming in Python

Python is a powerful object-oriented programming language. Therefore, creating and using objects is very easy. This article will introduce some basic concepts in object-oriented programming, as well as how to create and use them. Invites you to read the track.

Introducing OOP in Python

Object-oriented programming (English: Object-oriented programming) (OOP) is a support technique that allows programmers to directly work with objects they define. The effectiveness of this technique increases productivity, simplifies maintenance complexity as well as software expansion. Currently there are many object-oriented programming languages ​​such as C ++, Java, PHP, . and also Python.

Python's OOP concept focuses on creating reusable code. This concept is also called DRY (Don't Repeat Yourself).

Principles

In Python, the concept of OOP follows some basic principles: encapsulation, inheritance and polymorphism .

Inheritance : allows a class (class) to inherit properties and methods from other defined classes.

Encapsulation : is a rule that requires the internal state of an object to be protected and accessible from outside code (ie the external code cannot directly see and change the state of the object). that object).

Polymorphism: A concept in which two or more classes have similar methods but can be implemented in different ways.

Class (Class) and Object (Object)

Class and Object are two basic concepts in object-oriented programming.

Objects (Object) are existent entities with behaviors.

For example, the object is a car with its name, color, type of material, behavior going on, stopping, parking, exploding .

Class (Class) is a special type of data defined by the user, gathering many attributes specific to all objects created from that class.

Attributes are the values ​​of the class. Later when objects are created from the class, the class properties now become the features of that object.

Distinguish between Objects (Object) and Class (Class):

Object (Object): has state and behavior.

Class (Class): can be defined as a template that describes the state and behavior that the object type of the class supports. An object is an instance of a class

Object-oriented programming in Python Picture 1

Examples of Class and Object:

 class Car: 
 
  # thuộc tính lớp 
  loaixe = "Ô tô" 
 
  # thuộc tính đối tượng 
  def __init__(self, tenxe, mausac, nguyenlieu): 
  self.tenxe = tenxe 
  self.mausac = mausac 
  self.nguyenlieu = nguyenlieu 
 
 # instantiate the Car class 
 toyota = Car("Toyota", "Đỏ", "Điện") 
 lamborghini = Car("Lamborghini", "Vàng", "Deisel") 
 porsche = Car("Porsche", "Xanh", "Gas") 
 
 # access the class attributes 
 print("Porsche là {}.".format(porsche.__class__.loaixe)) 
 print("Toyota là {}.".format(toyota.__class__.loaixe)) 
 print("Lamborghini cũng là {}.".format(lamborghini.__class__.loaixe)) 
 
 # access the instance attributes 
 print("Xe {} có màu {}. {} là nguyên liệu vận hành.".format( toyota.tenxe, toyota.mausac, toyota.nguyenlieu)) 
 print("Xe {} có màu {}. {} là nguyên liệu vận hành.".format( lamborghini.tenxe, lamborghini.mausac,lamborghini.nguyenlieu)) 
 print("Xe {} có màu {}. {} là nguyên liệu vận hành.".format( porsche.tenxe, porsche.mausac, porsche.nguyenlieu)) 

The returned result will be:

 Porsche là Ô tô. 
 Toyota là Ô tô. 
 Lamborghini cũng là Ô tô. 
 Xe Toyota có màu Đỏ. Điện là nguyên liệu vận hành. 
 Xe Lamborghini có màu Vàng. Deisel là nguyên liệu vận hành. 
 Xe Porsche có màu Xanh. Gas là nguyên liệu vận hành. 

The above program creates a Car class , then determines the properties and characteristics of the object

We access class properties using __class __. Loaixe. Class properties are shared for all instances of the class.

Similarly, we access the instance properties using toyota.tenxe, toyota.mausac and toyota.nguyenlieu.

However, instance attributes are different for each instance of a class.

Method

Methods (Methods) are functions defined inside the body of a class. They are used to identify the behavior of an object.

Example of Class and Method

 class Car: 
 
  # thuộc tính đối tượng 
  def __init__(self, tenxe, mausac, nguyenlieu): 
  self.tenxe = tenxe 
  self.mausac = mausac 
  self.nguyenlieu = nguyenlieu 
 
  # phương thức 
  def dungxe(self, mucdich): 
  return "{} đang dừng xe để {}".format(self.tenxe,mucdich) 
 
 def chayxe(self): 
  return "{} đang chạy trên đường".format(self.tenxe) 
 
  def nomay(self): 
 return "{} đang nổ máy".format(self.tenxe) 
 
 # instantiate the Car class 
 toyota = Car("Toyota", "Đỏ", "Điện") 
 lamborghini = Car("Lamborghini", "Vàng", "Deisel") 
 porsche = Car("Porsche", "Xanh", "Gas") 
 
 # call our instance methods 
 print(toyota.dungxe("nạp điện")) 
 print(lamborghini.chayxe()) 
 print(porsche.nomay()) 

Run the program, the screen will return results:

 Toyota đang dừng xe để nạp điện 
 Lamborghini đang chạy trên đường 
 Porsche đang nổ máy 

In this example, there are three methods: dungxe (), chayxe () and nomay (). They are called instance methods because they are called on an instance object (toyota, lamborghini, porsche).

Inheritance

Inheritance allows a class (class) to inherit properties and methods from other defined classes. The existing class is called the parent class, the newly generated class is called the subclass. The subclass inherits all elements of the superclass, which can extend inheritance elements and add new components.

 # Lớp cha 
 class Car: 
 
  # Constructor 
  def __init__(self, hangxe, tenxe, mausac): 
  # Lớp Car có 3 thuộc tính: tenxe, mausac, hang xe 
  self.hangxe = hangxe 
  self.tenxe = tenxe 
  self.mausac = mausac 
 
  # phương thức 
  def chayxe(self): 
  print ("{} đang chạy trên đường".format(self.tenxe)) 
 
  def dungxe(self, mucdich): 
  print ("{} đang dừng xe để {}".format(self.tenxe, mucdich)) 
 
 # Lớp Toyota mở rộng từ lớp Car. 
 class Toyota(Car): 
 
 def __init__(self, hangxe, tenxe, mausac, nguyenlieu): 
  # Gọi tới constructor của lớp cha (Car) 
 # để gán giá trị vào thuộc tính của lớp cha. 
  super().__init__(hangxe, tenxe, mausac) 
 
  self.nguyenlieu = nguyenlieu 
 
  # Kế thừa phương thức cũ 
  def chayxe(self): 
  print ("{} đang chạy trên đường".format(self.tenxe)) 
 
  # Ghi đè (override) phương thức cùng tên của lớp cha. 
  def dungxe(self, mucdich): 
  print ("{} đang dừng xe để {}".format(self.tenxe, mucdich)) 
  print ("{} chạy bằng {}".format(self.tenxe, self.nguyenlieu)) 
 
  # Bổ sung thêm thành phần mới 
 def nomay(self): 
  print ("{} đang nổ máy".format(self.tenxe)) 
 
 toyota1 = Toyota("Toyota", "Toyota Hilux", "Đỏ", "Điện") 
 toyota2 = Toyota("Toyota", "Toyota Yaris", "Vàng", "Deisel") 
 toyota3 = Toyota("Toyota", "Toyota Vios", "Xanh", "Gas") 
 
 toyota1.dungxe("nạp điện") 
 toyota2.chayxe() 
 toyota3.nomay() 

Results returned:

 Toyota Hilux đang dừng xe để nạp điện 
 Toyota Hilux chạy bằng Điện 
 Toyota Yaris đang chạy trên đường 
 Toyota Vios đang nổ máy 

This program creates two inheritance classes: the Car parent class and the Toyota subclass .

Declare the new constructor to assign values ​​to the properties of the parent class. The super () function precedes __init __ to call __init __ content of Car.

Toyota Class inherits the function chayxe () and dungxe () of the Car class and modifies a behavior expressed in dungxe () method. Then the subclass adds new element nomay () to extend inheritance.

Encapsulation

Using OOP in Python, we can restrict access to the inner state of the object. This prevents data from being modified directly, called packaging . In Python, we denote this private property by using an underscore as a prefix: '_' or '__'.

 class Computer: 
 
  def __init__(self): 
 # Thuộc tính private ngăn chặn sửa đổi trực tiếp 
  self.__maxprice = 900 
 
 def sell(self): 
 print("Giá bán sản phẩm: {}".format(self.__maxprice)) 
 
  def setMaxPrice(self, price): 
  self.__maxprice = price 
 
 c = Computer()c.sell() 
 
 # thay đổi giá. 
 c.__maxprice = 1000 
 c.sell() 
 
 # sử dụng hàm setter để thay đổi giá. 
 c.setMaxPrice(1000) 
 c.sell() 

Screen showing results:

 Selling Price: 900 
 Selling Price: 900 
 Selling Price: 1000 

In this example, you initialize the Computer class, use __init __ () to store the maximum selling price of the computer. But after use, you need to modify the price, but you can't change it in the normal way because Python has considered __maxprice as a private property. So to change the value, we use the setter function setMaxPrice ().

Polymorphism

Polymorphism is a concept where two or more classes have the same methods but can be implemented in different ways.

Suppose, we need to color a shape, there are many options for your shapes like rectangles, squares, circles. However, you can use the same method to color any shape.

 class Toyota: 
 
  def dungxe(self): 
  print("Toyota dừng xe để nạp điện") 
 
  def nomay(self): 
  print("Toyota nổ máy bằng hộp số tự động") 
 
 class Porsche: 
 
  def dungxe(self): 
  print("Porsche dừng xe để bơm xăng") 
 
  def nomay(self): 
  print("Porsche nổ máy bằng hộp số cơ") 
 
 # common interface 
 def # common interface 
 def kiemtra_dungxe(car): car.dungxe() 

 # instantiate objects 
 toyota = Toyota() 
 porsche = Porsche() 
 
 # passing the object 
 kiemtra_dungxe(toyota) 
 kiemtra_dungxe(porsche) 

In this example, you have just created two layers of Toyota and Porsche, both of which have a dungeon () method. Of course their functions are different. We use polymorphism to create common functions for two classes, that is kiemtra_dungxe (). Next, you pass the toyota and porsche object to the newly created function, and we get this result:

 Toyota dừng xe để nạp điện 
 Porsche dừng xe để bơm xăng 

So Quantrimang has just introduced you to the highlights of OOP. Through the article, some comments like this can be drawn:

1. Programming becomes easier and more efficient.
2. Class can be shared so the code is easily reused.
3. Productivity of the program increased
4. Data is safe and secure with data abstraction.

See more:

1. Steve Jobs defines object-oriented programming to make the world admire
2. Object-oriented programming in PHP

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