Python Simple and Multiple Inheritance

What is inheritance in python?

• Inheritance is the process by which one object acquires the properties of another object.
• Inheritance is a mechanism in which one object acquires all the properties and functionalities of parent object.
• It allows to create the hierarchical classifications.
• Using inheritance, create a general class (is also called superclass or baseclass) that defines common set of related items. This class can then be inherited by other class(subclass).
• A subclass is a specialized version of base class.
• All methods in Python are effectively virtual in default. methods can be overridden in derived classes.

Inheritance syntax in python

class DerivedClass(BaseClass):
    statement1
    .
    .
    .
    statementN

Base class is defined in another module

class DerivedClass(module_name.BaseClassName):

super() method in python

super().method_name(arguments);

Example Python Inheritance Program

class Parent:                                                                   
    def __init__(self, a, b):                                                   
        self.a = a;                                                             
        self.b = b;                                                             
                                                                                
    def showab(self):                                                           
        print("a and b: %d %d" %  (self.a, self.b));                                                                                                                                                                
               
# Inheritance Child is the subclass and Parent is the base class                                                 
class Child(Parent):                                                            
    def __init__(self, a, b, c):                                                
        super().__init__(a, b);                                                 
        self.c = c;                                                             
                                                                                
    def showc(self):                                                            
        print("c: %d" % self.c);                                                
                                                                                
    def sum(self):                                                              
        print("sum(a+b+c): %d" % (self.a+self.b+self.c));                       
                                                                                
                                                                                
superObj = Parent(20, 30);                                                      
subObj = Child(11, 12, 13);                                                     
superObj.showab();                                                              
                                                                                
subObj.showab();                                                                
subObj.showc();                                                                 
subObj.sum();

$ python3 inheritance_test.py
a and b: 20 30
a and b: 11 12
c: 13
sum(a+b+c): 36

Multiple Inheritance in python

class DerivedClass(Base1, Base2, Base3):
    statement1
    .
    .
    .
    statementN

Example Multiple Inheritance Python Program

class Parent1:                                                                  
    def __init__(self, a, b):                                                   
        self.a = a;                                                             
        self.b = b;                                                             
                                                                                
    def showab(self):                                                           
        print("a and b: %d %d" %  (self.a, self.b));                                                                                                                                                                
class Parent2:                                                                  
    def __init__(self, c, d):                                                   
        self.c = c;                                                             
        self.d = d;                                                             
                                                                                
    def showcd(self):                                                           
        print("c and d: %d %d" %  (self.c, self.d));                            
     
# multiple inheritance                                                                           
class Child(Parent1, Parent2):                                                  
    def __init__(self, a, b, c, d, e):                                          
        Parent1.__init__(self, a, b);                                           
        Parent2.__init__(self, c, d);                                           
        self.e = e;                                                             
                                                                                
    def showc(self):                                                            
        print("e: %d" % self.e);                                                
                                                                                
    def sum(self):                                                              
        print("sum(a+b+c+d+e): %d" % (self.a+self.b+self.c+self.d+self.e));     
                                                                                
                                                                                
superObj1 = Parent1(20, 30);                                                    
superObj2 = Parent2(40, 50);                                                    
subObj = Child(11, 12, 13, 14, 15);                                             
superObj1.showab();                                                             
superObj2.showcd();                                                             
                                                                                
subObj.showab();                                                                
subObj.showcd();                                                                
subObj.showc();                                                                 
subObj.sum();   

$ python3 inheritance_test1.py 
a and b: 20 30
c and d: 40 50
a and b: 11 12
c and d: 13 14
e: 15
sum(a+b+c+d+e): 65

Two built-in functions for inheritance in python

• isinstance() method is used to check an instance’s type.

   isinstance(obj, class1) 
  

  True only if obj.__class__ is class1 or some class derived from class1.
• issubclass() method is used to check class inheritance.

  issubclass(class1, class2) 
  

  True since class1 is a subclass of class2.

  issubclass(class1, class2) 
  

  False since class1 is not a subclass of class2.

class Parent1:                                                                  
    def __init__(self, a, b):                                                   
        self.a = a;                                                             
        self.b = b;                                                             
                                                                                
    def showab(self):                                                           
        print("a and b: %d %d" %  (self.a, self.b));                                                                                                                                                                
class Parent2:                                                                  
    def __init__(self, c, d):                                                   
        self.c = c;                                                             
        self.d = d;                                                             
                                                                                
    def showcd(self):                                                           
        print("c and d: %d %d" %  (self.c, self.d));                            
                                                                                
class Child(Parent1, Parent2):                                                  
    def __init__(self, a, b, c, d, e):                                          
        Parent1.__init__(self, a, b);                                           
        Parent2.__init__(self, c, d);                                           
        self.e = e;                                                             
                                                                                
    def showc(self):                                                            
        print("e: %d" % self.e);                                                
                                                                                
    def sum(self):                                                              
        print("sum(a+b+c+d+e): %d" % (self.a+self.b+self.c+self.d+self.e));     
                                                                                
                                                                                
superObj1 = Parent1(20, 30);                                                    
superObj2 = Parent2(40, 50);                                                    
subObj = Child(11, 12, 13, 14, 15);                                             
                                                                                
if isinstance(superObj1, Parent1):                                              
    print("superObj1 is instance of Class Parent1");                           
                                                                                
if issubclass(Child, Parent1):                                                  
    print("Child class is sub class of Class Parent1");                        
                                                                                
if issubclass(Child, Parent2):                                                  
    print("Child class is sub class of Class Parent2");   

$ python3 inheritance_test1.py 
superObj1 is instance of Class Parent1
Child class is sub class of Class Parent1
Child class is sub class of Class Parent2