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Python Programming
CLASSES AND OBJECTS IN PYTHON

CLASSES AND OBJECTS IN PYTHON ❤️

Python is an object oriented programming (OOP) language and it provides all the features required to support object-oriented programming .

OOP mainly focuses on class and objects.

Class 🔊

Classes are defined by the user. The class provides the basic structure for an objec.Class is a collection of data(variables) and methods(functions).A class can be defined as a blue print or a previously defined structure from which objects are made.

NOTE : 💡

  • In python, a class is defined by using keyword "class".
  • As soon as we define a class, the interpreter instantly creates an object that has the same name as the class name.
  • Attributes are the variables that belong to class.
  • Attributes are always public and can be accessed using dot(.) operator.

Syntax 🔖

class class_name:

 statements

Example 1 💻

class age :
    x=10
print(age)
<class '__main__.age'>

Objects

  • An object is an instace of a class that has some attributes and behaviour.
  • The object behaves according to the class of which it is an object.
  • Objects can be used to access the attributes of the class.

An object consists of :

  1. State : It is representated by attributes of an object. It also reflects the properties of an object.
  2. Behavior : It is represented by methods of an object. It also reflects the response of an object with other objects.
  3. Identity : It gives a unique name to an object and enables one object to interact with other objects.

Syntax 🔖

obj_name = class_name()

Example 💻

class age :
    x=10
print(age)

age1 = age () #object instantiation
<class '__main__.age'>

Example 2 💻

#sample class
class student :
    id = 100     #attribute
    name = "Mike" #attribute
    
    def display(self):  #a sample method
        print("ID : %d \nName : %s" %(self.id, self.name))
    
stud = student()  # creating an object of student class
stud.display()
ID : 100 
Name : Mike

In the above example, an object is created which is basically student named stud. This class has two attributes that tells that stud has id 100 and name Mike.

NOTE : 💡

The self parameter is a refrence to the current instance of the class, and is used to access variables that belongs to the class.

Self Parameter

  • Is similar to this pointer in c++ and reference in java.
  • Self represents the instance of the class.

Example 💻

class Student:
    def say_marks(self):
        print("Argh! I scored 100!")
    def studies(self,hours):
        
        print("No_hrs:",hours,end="")

student1 = Student()

student1.say_marks()

hours = int(input())

student1.studies(hours)
Argh! I scored 100!
8
No_hrs: 8

init() function

  • init method is similar to constructors in c++ and java.
  • Use of init() function to assign values to object properties, or other operations that are necessary to do when the object is being created.

Example 1 💻

class student:
    def __init__(name,school) :
        name.school = school

s1 = student("Mike")
print(s1.school)
Mike

Example 2 💻

#this example shows to modify object proprties
class student:
    def __init__(name,school,city) :
        name.school = school
        name.city=city
    
    def func(name):
        print("Hello my name is " +name.school)

s1 = student("Mike", "Bangalore")
s1.func()
print(s1.school)
print("previous city of my school is ", s1.city)
s1.city= "Mysore"
print("new city of my school is", s1.city)
Hello my name is Mike
Mike
previous city of my school is  Bangalore
new city of my school is Mysore

Delete object properties

We can delete properties on objects by using del keyword

Example 💻

class student:
    def __init__(name,school,city) :
        name.school = school
        name.city=city
    
    def func(name):
        print("Hello my name is " +name.school)

s1 = student("Mike", "Bangalore")
del s1
print(s1.school)
#having an empty class definition like this, would raise an error without the pass statement.
---------------------------------------------------------------------------

NameError                                 Traceback (most recent call last)

<ipython-input-7-88ab8982e316> in <module>
      9 s1 = student("Mike", "Bangalore")
     10 del s1
---> 11 print(s1.school)
     12 #having an empty class definition like this, would raise an error without the pass statement.


NameError: name 's1' is not defined

Objects are mutable 💡

  • The state of an object can be changed at any point of time by making changes to its attributes.

Now let's look into calculator example using classes and objects. ➕

class Calculator:
    def sum(self,sum_list):
        sum=0
        for i in range(0,len(sum_list)):
            sum=sum+sum_list[i]
        return sum
    def minus(self,first,second):
       
        return first-second
    def multiply(self,sum_list):
        d=1
        for i in range(0,len(sum_list)):
            
            d=d*sum_list[i]
        return d
    def divide(self,fourth,fifth):
        if(fifth==0):
            return "Div by 0 not allowed!"
        else:
            b=fourth//fifth
            return b
        
calc = Calculator()
print("Enter your numbers for calculation")
first = int(input())
second = int(input())
third = int(input())
fourth = int(input())
fifth = int(input())

sum_list = [first,second,third,fourth,fifth]
answer_1 = calc.sum(sum_list)
print(f"Sum of {sum_list} is {answer_1}")

answer_2 = calc.minus(first,second)
print(f"{first} - {second} = {answer_2}")

answer_3 = calc.multiply(sum_list[:-1]) # selecting only first 4 values
print(f"Multiplying {sum_list[:-1]} = {answer_3}")

answer_4 = calc.divide(fourth,fifth)
print(f"Dividing {fourth}/{fifth} = {answer_4}")
Enter your numbers for calculation
89
56
54
123
69
Sum of [89, 56, 54, 123, 69] is 391
89 - 56 = 33
Multiplying [89, 56, 54, 123] = 33103728
Dividing 123/69 = 1