Python Objects and Classes

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Index

1. Definition
2. Classes
3. Objects
4. Access class attributes using Objects
5. Python Methods
6. Python Constructors

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Definition

• An object is simply a collection of data (variables) and methods (functions).
• A class is a blueprint for that object.

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Classes

Syntax:

class ClassName:
    # class definition 

Example:

class Bike:
    name = ""
    gear = 0

• Bike - the name of the class
• name/gear - variables inside the class with default values "" and 0 respectively.

Note

The variables inside a class are called attributes.

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Objects

An object is called an instance of a class. For example, suppose Bike is a class then we can create objects like bike1, bike2, etc from the class.

Syntax:

objectName = ClassName()

Example:

# create class
class Bike:
    name = ""
    gear = 0
 
# create objects of class
bike1 = Bike()

Here, bike1 is the object of the class. Now, we can use this object to access the class attributes.

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Access class attributes using Objects

We use the . notation to access the attributes of a class.

# modify the name attribute
bike1.name = "Mountain Bike"
 
# access the gear attribute
bike1.gear

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Python Methods

We can also define a function inside a Python class. A Python Function defined inside a class is called a method.

Example:

# create a class
class Room:
    length = 0.0
    breadth = 0.0
    
    # method to calculate area
    def calculate_area(self):
        print("Area of Room =", self.length * self.breadth)
 
# create object of Room class
study_room = Room()
 
# assign values to all the attributes 
study_room.length = 42.5
study_room.breadth = 30.8
 
# access method inside class
study_room.calculate_area()

Output:

Area of Room = 1309.0

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Python Constructors

Earlier we assigned a default value to a class attribute,

class Bike:
    name = ""
...
# create object
bike1 = Bike()

However, we can also initialise values using the constructors. For example:

class Bike:
 
    # constructor function    
    def __init__(self, name = ""):
        self.name = name
 
bike1 = Bike()

Here, __init__() is the constructor function that is called whenever a new object of that class is instantiated.

The constructor above initializes the value of the name attribute. We have used the self.name to refer to the name attribute of the bike1 object.

If we use a constructor to initialize values inside a class, we need to pass the corresponding value during the object creation of the class.

bike1 = Bike("Mountain Bike")

Here, "Mountain Bike" is passed to the name parameter of __init__().

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