Inheritance (Inheritance) in Python

Inheriting in object-oriented programming allows us to declare new classes to re-use the parent class's functions and attributes and extra functions. In this article, we will learn how to use legacy in Python.

What is inheritance?

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

Syntax of inheritance

 class BaseClass: 
  Body of base class 
 
 class DerivedClass(BaseClass): 
  Body of derived class 

For more clarity about using inheritance, let's take an example.

Polygon is a closed shape with 3 or more sides. We have a class called DaGiac defined as follows.

 class DaGiac: 
 
  def __init__(self, socanh): 
  self.n = socanh 
  self.canh = [0 for i in range(socanh)] 
 
  def nhapcanh(self): 
  self.canh = [float(input("Bạn hãy nhập giá trị cạnh "+str(i+1)+" : ")) for i in range(self.n)] 
 
  def hienthicanh(self): 
  for i in range(self.n): 
  print("Giá trị cạnh",i+1,"là",self.canh[i]) 

Class DaGiac has the n attribute to define the number of edges and edges to store each edge value. The nhapcanh () function takes the size of the edges and hienthicanh () will display the list of polygons.

The triangle is polygon with three sides, so we will create a class TamGiac inherited from DaGiac. This new class will inherit all the properties available in the superclass, so you won't need to re-declare (reuse code). This TamGiac is declared as follows:

 class TamGiac(DaGiac): 
 
  def __init__(self): 
  DaGiac.__init__(self,3) 
 
  def dientich(self): 
  a, b, c = self.canh 
  # Tính nửa chu vi 
  s = (a + b + c) / 2 
  area = (s*(sa)*(sb)*(sc)) ** 0.5 
  print('Diện tích của hình tam giác là %0.2f' %area) 

The TamGiac class not only inherits but also defines a new function as the dientich function .

 >>> t = TamGiac() 
 >>> t.nhapcanh() 
 Bạn hãy nhập giá trị cạnh 1 : 3 
 Bạn hãy nhập giá trị cạnh 2 : 5 
 Bạn hãy nhập giá trị cạnh 3 : 4 
 
 >>> t.hienthicanh() 
 Giá trị cạnh 1 là 3.0 
 Giá trị cạnh 2 là 5.0 
 Giá trị cạnh 3 là 4.0 
 
 >>> t.dientich() 
 Diện tích của hình tam giác là 6.00 

We can see that the functions nhapcanh (), hienthicanh () are not in TamGiac class, but we still use them

Overriding in Python

Python allows to override parent class methods. You can perform the override of the parent class method if you want to have special or special features in the subclass.

In the above example, we see that the TamGiac class uses the __init __ () function from the DaGiac class , if you want to override the definition of __init __ () function in the parent class, we use the super () function.

super () .__ init __ (3) is equivalent to DaGiac .__ init __ (self, 3)

Also Python has two isinstance () and issubclass () functions that are used to test the relationship of two classes and instances.

The issubclass function (classA, classB) returns True if class A is a subclass of class B.

 >>> issubclass(DaGiac,TamGiac) 
 False 
 
 >>> issubclass(TamGiac,DaGiac) 
 True 
 
 >>> issubclass(bool,int) 
 True 

The isinstance (obj, Class) function returns True if obj is an instance of Class or is an instance of Class's subclass.

 >>> isinstance(t,TamGiac) 
 True 
 
 >>> isinstance(t,DaGiac) 
 True 
 
 >>> isinstance(t,int) 
 False 
 
 >>> isinstance(t,object) 
 True 
 

See more:

1. Object-oriented programming in Python
2. Manage files and folders in Python
3. Learn about Error and Exception

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