Inheritance in Python

Introduction to Inheritance

1. Inheritance describes is a kind of relationship between two or more classes, In general getting and storing specific details in the subclass from super class.

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

Example :
Class ChildClass(ParentClass):

pass

3. Every child class inherits all the behaviors exhibited by their parent class.

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

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

Definition 1

class MySubClass:

pass

Definition 2

class MySubClass(object):

pass

1. “object” is known as parent or super class.

2. “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”.

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

1. In the above example, Employee class utilizes __init __ method of the parent class Person to create its object.

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

3. 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 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']