Solving a problem by creating objects is one of the most popular approaches in programming. This is called object-oriented programming.This concept focuses on using reusable code. (Implements DRY principle)
Class
A class is a blueprint for creating objects.
The syntax of a class looks like this:
Class Employee: [classname is written in PascalCase]
#methods & variables
Object
An object is an instantiation of a class. When class is defined, a template(info) is defined. Memory is allocated only after object instantiation.
Objects of a given class can invoke the methods available to it without revealing the implementation details to the user. #Abstraction & Encapsulation!
Modelling a problem in OOPs
We identify the following in our problem
Noun -> Class -> Employee
Adjective -> Attributes -> name,age,salary
Verbs -> Methods -> getSalary(), increment()
Class Attributes
An attribute that belongs to the class rather than a particular object.
Example:
Class Employee:
company = “Google” #Specific to each class
harry = Employee() #Object instantiation
harry.company
Employee.company = “YouTube” #changing class attribute
Instance Attributes
An attribute that belongs to the Instance (object)
Assuming the class from the previous example:
harry.name = “Harry”
harry.salary = “30K” #Adding instance attributes
Note: Instance attributes take preference over class attributes during assignment and retrieval.
‘self’ parameter:
self refers to the instance of the class.
It is automatically passed with a function call from an object.
harry.getSalary()
here, self is harry and above line of code is equivalent to Employee.getSalary(harry)
This function getsalary is defined as:
class Employee:
company = “Google”
def getSalary(self):
print(“Salary is not there”)
Static method:
Sometimes we need a function that doesn’t use the self-parameter. We can define a static method like this:
@staticmethod #decorator to mark greet as a static method
def greet():
print(“Hello user”)
__init__() constructor:
- __init__() is a special method which runs as soon as the object is created.
- __init__() method is also known as constructor.
- It takes self-argument and can also take further arguments.
For Example:
class Employee:
def __init__(self,name):
self.name = name
def getSalary(self):
#Some code…
harry = Employee(“Harry”) #Object can be instantiated using constructor like this!
Practice:
Create a class programmer for storing information of a few programmers working at Microsoft.
class Programmer:
company = "Microsoft"
def __init__(self,name,product):
self.name=name
self.product=product
def getInfo(self):
print(f"name of the companty {self.company} and name is {self.name} and product is {self.product}")
sri=Programmer("Sri","Skype")
nanda=Programmer("Nannda","Outlook")
print(sri.getInfo())
print(nanda.getInfo())
Write a class calculator capable of finding square, cube and the square root of a number.
class Calculator:
def __init__(self,num):
self.num=num
def getSquare(self):
return self.num * self.num
def getCube(self):
return self.num ** 3
def getSqrRoot(self):
return self.num * 0.5
c=Calculator(5)
print(c.getSquare())
print(c.getCube())
print(c.getSqrRoot())
Create a class with a class attribute a; create an object from it and set a directly using object.a=0 Does this change the class attribute?
class Sample:
a=23
s = Sample()
s.a=0
print(Sample.a)
print(s.a)
Answer: No, This will not change the class attribute.
Add a static method in problem 2 to greet the user with hello.
class Calculator:
def __init__(self,num):
self.num=num
def getSquare(self):
return self.num * self.num
def getCube(self):
return self.num ** 3
def getSqrRoot(self):
return self.num * 0.5
@staticmethod
def greetUser():
print("Hello user")
c=Calculator(5)
c.greetUser()
print(c.getSquare())
print(c.getCube())
print(c.getSqrRoot())
Write a class Train which has methods to book a ticket, get status(no of seats), and get fare information of trains running under Indian Railways.
class Train:
def __init__(self, name, fare, seats):
self.name = name
self.fare = fare
self.seats = seats
def getStatus(self):
print("************")
print(f"The name of the train is {self.name}")
print(f"The seats available in the train are {self.seats}")
print("************")
def fareInfo(self):
print(f"The price of the ticket is: Rs {self.fare}")
def bookTicket(self):
if(self.seats>0):
print(f"Your ticket has been booked! Your seat number is {self.seats}")
self.seats = self.seats - 1
else:
print("Sorry this train is full! Kindly try in tatkal")
def cancelTicket(self, seatNo):
pass
intercity = Train("Intercity Express: 14015", 90, 2)
intercity.getStatus()
intercity.bookTicket()
intercity.bookTicket()
intercity.bookTicket()
intercity.getStatus()
