22 Feb Python Classes and Objects

Posted at 00:01h in Python3 by

Python is an interpreted high-level, structural, and object-oriented programming language. Since it is object-oriented, the concept of classes and objects is well-discussed and implemented. A class is the basis of object-oriented programming in Python. In this tutorial, we will learn about Classes and Objects in Python. A class is a template for an object, whereas an object is an instance of a class.

What is a class in Python

As discussed above, a class is a blueprint for objects in Python. We can easily create a class like this:

class name_of_class:
# Statement1
# Statement2
# Statement3
.
.
.
StatementN

Example 1 – Create a Class in Python

The class keyword is used to create a class in Python. The class is a reserved word in Python.

In the example below, we will see how to create a class in Python:

Demo85.py

# creating a class with a property val
# the class keyword is used to create a class
class Studyopedia:
  val = 100

print(Studyopedia)

Output

<class '__main__.Studyopedia'>

What is an object in Python?

An object is an instance of a class, i.e. object is created from a class. An object represents real-life entities, for example, a Bike is an object. The object has State, Behavior, and Identity:

  • Identity: Name of Bike
  • State (Attributes): The data of the object Bike i.e. Color, Model, Weight, etc.
  • Behavior (Methods): Behavior of object Bike like to Drive, Brake

Let us now see the representation, with Bike as an object:

Python Objects

Example 2 – How to Create a Class and an Object in Python

Considering the above example of classes in Python, we can easily create an object.

Demo86.py

# creating a class with a property val
# the class keyword is used to create a class
class Studyopedia:
  val = 100

print(Studyopedia)

# object ob
ob = Studyopedia()

# displaying the value using the object ob
print("Value = ",ob.val)

Output

<class '__main__.Studyopedia'>
Value =  100

Now, we can easily create a sample Python program on Classes and Objects. Let’s see.

Example 3 – Python Classes and Objects

Let us see an example to implement classes and objects in Python. In the class, we have used a function parameter self.

In Python, self is a special convention used inside class methods to refer to the current instance of the class.

Demo87.py

# class
class Bike:
     
    # attributes of Bike
    name = "Hayabusa"
    body = "GEN III"
    engine = 1340
 
    # Custom Python function
    def demoFunc(self):
        print("\nBike = ", self.name)
        print("Body = ", self.body)
        print("Engine (cc) = ", self.engine)
 
# Objects
b1 = Bike()
b2 = Bike()
 
# Accessing using the 1st object
print("Bike name = ",b1.name)
print("Bike Engine = ",b1.engine)

# calling using the 2nd object
b2.demoFunc()

Output

Bike name =  Hayabusa
Bike Engine =  1340

Bike =  Hayabusa
Body =  GEN III
Engine (cc) =  1340

Example 4 – Python Classes and Objects

# Classes and Objects in Python
# Example 3

class Car:
      # attributes of Car
      # class variables
      brand = "Tesla"
      model = "S"
      engine = 1020

      def show(self):
          print("Car Brand = ",self.brand)
          print("Model =",self.model)
          print("Engine =",self.engine)

# Class objects
c1 = Car()
c2 = Car()

# Access using the 1st object
print(c1.brand)
print(c1.model)

# call using the 2nd object
c2.show() # self refers to c2 because we are calling show() using c2

c1.brand = "Kia"
c1.model = "Sonet"
c1.engine = 1100
print(c1.brand)
print(c1.model)
print(c1.engine)

c2.brand = "Hyundai"
c2.model = "i20"
c2.engine = 1000
print(c1.brand)
print(c1.model)
print(c1.engine)

Output

Tesla
S
Car Brand =  Tesla
Model = S
Engine = 1020
Kia
Sonet
1100
Kia
Sonet
1100

What self Does

  • It represents the object that is calling the method.
  • It allows you to access attributes and methods of that particular object.
  • Without self, methods wouldn’t know which object’s data they should work with.

Key Points

  • self must be the first parameter in instance methods.
  • You can technically name it anything (like this or obj), but by convention, Python developers always use self.
  • When you call a method on an object, Python automatically passes the object itself as the first argument to the method.

Python _init_() Function

The classes in Python have __init__() function. Like constructors in Java, the __init__() function executes when the object gets created.

Why do we need __init__?

Using this method, easily assign values to object properties.

It’s a special method, often called a constructor, that gets executed automatically when you create an object from a class. Its purpose is to initialize the object’s attributes with default or user-provided values. The __init()__ is needed if you want to set up initial values for attributes when an object is created.

Use __init__() if you want to set up initial values for attributes when an object is created. The purpose of __init__() is to initialize the object’s attribute with default or user-provided values.

What if __init__ is not defined?

  • Python will still create the object even if you don’t define __init__().
  • If you don’t provide one, Python uses a default constructor that does nothing special.

So, __init__() is optional, but it’s extremely useful for making your classes flexible and meaningful.

Let us understand with an example, wherein we will create a class Students and values will be assigned using the __init__(). We have also created object functions.

Also, we created the objects explicitly in this example:

  • st1, st2, and st3 are variables that hold references to three different Students objects.
  • Each time we call Students(...), Python runs the __init__ method and assigns values to the object’s attributes.

Demo88.py

# Python __init__() Function
# init is short for initialization

class Students:
    # Use __init__(), if you want to setup initial values for attributes when an object is created.
    # the purpose of __init__ is to initialize the object's attribute with default or user-provided values.
    def __init__(self,sname, ssub, sgrade):
        self.sname = sname
        self.ssub = ssub
        self.sgrade = sgrade

    # custom function
    def demofunc(self):
        print("I am "+self.sname)
        print("I am interested in the Subject = "+self.ssub)

# creating 3 objects
st1 = Students("Amit", "Programming", "A")
st2 = Students("Rohit", "Science", "A+")
st3 = Students("Sam", "Maths", "B")

st1.demofunc()
st2.demofunc()
st3.demofunc()

Output

I am Amit
I am interested in the Subject = Programming
I am Rohit
I am interested in the Subject = Science
I am Sam
I am interested in the Subject = Maths

Above, we have also used the self parameter. The class methods in Python have the first parameter as self to access the class variable. A method with no argument should also have an argument self. However, we can give it any name. It is not mandatory to use the word self.

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