Inheritance in Python

Rumman Ansari   Software Engineer   2022-10-10   356 Share
☰ Table of Contents

Table of Content:

What is Inheritance?

  • Inheritance describes is a kind of relationship between two or more classes, abstracting common details into super class and storing specific ones in the subclass.

  • To create a child class, specify the parent class name inside the pair of parenthesis, followed by it's name.

Example


 class Child(Parent):  
   pass
  • Every child class inherits all the behaviours exhibited by their parent class.

Inheritance

  • In Python, every class uses inheritance and is inherited from object by default.

  • Hence, the below two definitions of MySubClass are same.

Definition 1

class MySubClass:   
   pass

Definition 2

class MySubClass(object):   
    pass

  • object is known as parent or super class.

  • MySubClass is known as child or subclass or derived class.

Inheritance in Action
class Person:
    def __init__(self, fname, lname):
        self.fname = fname
        self.lname = lname
class Employee(Person):
    all_employees = []
    def __init__(self, fname, lname, empid):
        Person.__init__(self, fname, lname)
        self.empid = empid
        Employee.all_employees.append(self)
  • Employee class is derived from Person.
Inheritance in Action
p1 = Person('George', 'smith')
print(p1.fname, '-', p1.lname)
e1 = Employee('Jack', 'simmons', 456342)
e2 = Employee('John', 'williams', 123656)
print(e1.fname, '-', e1.empid)
print(e2.fname, '-', e2.empid)

Output

George - smith
Jack - 456342
John - 123656
  • In the above example, Employee class utilizes __init __ method of the parent class Person to create its object.
Extending Built-in Types

  • Inheritance feature can be also used to extend the built-in classes like list or dict.

  • The following example extends list and creates EmployeesList, which can identify employees, having a given search word in their first name.

Example 1


 class EmployeesList(list):
    def search(self, name):
        matching_employees = []
        for employee in Employee.all_employees:
            if name in employee.fname:
                matching_employees.append(employee.fname)
        return matching_employees
Extending Built-in Types

Extending Built-in Types EmployeesList object can be used to store all employee objects, just by replacing statement all_employees = [] with all_employees = EmployeesList().

Example 2


 class Employee(Person):
    all_employees = EmployeesList()
    def __init__(self, fname, lname, empid):
        Person.__init__(self, fname, lname)
        self.empid = empid
        Employee.all_employees.append(self)

e1 = Employee('Jack', 'simmons', 456342)
e2 = Employee('George', 'Brown', 656721)
print(Employee.all_employees.search('or'))

Output

 
['George']
‹ Previous not possible this is first one.
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