Creating Instance Objects in Python

In Python, an instance object is an individual object created from a class, which serves as a blueprint defining the attributes (data) and methods (functions) for the object. When we create an object from a class, it is referred to as an instance. Each instance has its own unique data but shares the class's methods. Example:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

# instance of the class
a = Person("John Doe", 25)

# Accessing attributes
print(a.name)  
print(a.age)  

John Doe
25

Explanation:

• __init__ method takes two parameters, name and age and initializes them for each instance.
• We then create an instance called a and pass the values "John Doe" and 25 to the constructor.
• We can access the instance's attributes using dot notation, such as a.name and a.age.

Syntax of creating instance objects

class ClassName:

def __init__(self, parameters):

# constructor code here

# initialize instance variables

# Create an instance of the class

instance_object = ClassName(parameters)

• ClassName: The name of the class.
• __init__: The constructor method, responsible for initializing the instance.
• self: A reference to the instance itself.
• parameters: Any data that needs to initialize the instance.

When you instantiate a class, the __init__ method is called to initialize the object’s attributes.

Examples of creating instance object

Example 1: In this example, we define a simple Car class to represent a car with basic attributes like make, model and year. We also add a method to simulate driving the car, which increases its mileage.

class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year
        self.mileage = 0  # Mileage starts at 0

    def drive(self, distance):
        self.mileage += distance

a = Car("Toyota", "Camry", 2022) # Car object

print(f"{a.make} {a.model} ({a.year})")
a.drive(100)
print(f"Mileage: {a.mileage} miles")

Toyota Camry (2022)
Mileage: 100 miles

Explanation:

• Car class has attributes for make, model, year and mileage.
• drive() method increases the mileage by the given distance.
• We create an instance a of the Car class and drive it for 100 miles.

Example 2: In this example, we create a base class Animal and a derived class Dog. We use super() to call the parent class constructor and set the species to "Dog" by default.

class Animal:
    def __init__(self, species):
        self.species = species  # Base class attribute

class Dog(Animal):
    def __init__(self, name, age):
        super().__init__("Dog")  # Set species as 'Dog'
        self.name = name
        self.age = age

dog = Dog("Buddy", 3) # Dog instance

print(f"{dog.name} is a {dog.species} of age {dog.age} years")

Buddy is a Dog of age 3 years

Explanation:

• Animal is a base class with one attribute species.
• Dog inherits from Animal and uses super() to set species as "Dog".
• dog object has a name and age along with inherited species.

Example 3: This example demonstrates encapsulation by using double underscores (__) to make the balance attribute private. The class provides methods to deposit, withdraw and view the balance securely.

class Bank:
    def __init__(self, name, bal=0):
        self.name = name
        self.__bal = bal

    def deposit(self, amt):
        if amt > 0: self.__bal += amt

    def withdraw(self, amt):
        if 0 < amt <= self.__bal: self.__bal -= amt

    def get_bal(self):
        return self.__bal

acc = Bank("Alice", 500)
acc.deposit(200)
acc.withdraw(150)
print(acc.get_bal()) 

550

Explanation:

• __bal attribute is private, meaning it cannot be accessed directly from outside the class.
• methods deposit(), withdraw() and get_bal() provide safe access and modification to the balance.
• After depositing 200 and withdrawing 150, the final balance is 550.