Constructors in Python

Constructors are special methods used to initialize objects when they are created from a class. Object creation and initialization are handled through the __new__() and __init__() methods. Constructors help assign initial values to object attributes and prepare objects for use.

When an object is created:

• The __new__() method creates and returns a new instance of the class.
• The __init__() method initializes the newly created object.
• The object becomes ready for use.

__new__() Method

This method is responsible for creating a new instance of a class. It allocates memory and returns the new object. It is called before __init__.

Syntax:

class ClassName:
    def __new__(cls, parameters):
        instance = super(ClassName, cls).__new__(cls)
        return instance

To learn more, please refer to this article: __new__

__init__() Method

This method initializes the newly created instance and is commonly used as a constructor in Python. It is called immediately after the object is created by __new__ method and is responsible for initializing attributes of the instance.

Syntax:

class ClassName:
    def __init__(self, parameters):
        self.attribute = value

Note: It is called after __new__ and does not return anything (it returns None by default).

To learn more, please refer to this article: __init__

Differences Between __init__ and __new__

Types of Constructors

Constructors can be of two types.

1. Default Constructor

A default constructor does not take any parameters other than self. It initializes the object with default attribute values.

class Car:
    def __init__(self):

        #Initialize the Car with default attributes
        self.make = "Toyota"
        self.model = "Corolla"
        self.year = 2020

# Creating an instance using the default constructor
car = Car()
print(car.make)
print(car.model)
print(car.year)

Toyota
Corolla
2020

Note: If no constructor is defined in a class, Python automatically provides a default constructor that creates the object without initializing custom attributes.

Explanation:

• Define Constructor: __init__() is defined without additional parameters.
• Initialize Attributes: Default values are assigned to make, model, and year.
• Create Object: Car() automatically invokes the constructor.
• Access Attributes: Object attributes are printed using dot notation.

2. Parameterized Constructor

A parameterized constructor accepts arguments to initialize the object's attributes with specific values.

class Car:
    def __init__(self, make, model, year):
      
        #Initialize the Car with specific attributes.
        self.make = make
        self.model = model
        self.year = year

# Creating an instance using the parameterized constructor
car = Car("Honda", "Civic", 2022)
print(car.make)
print(car.model)
print(car.year)

Honda
Civic
2022

Explanation:

• Accept Parameters: The constructor receives make, model, and year as arguments.
• Assign Values: Constructor arguments are assigned to instance attributes.
• Create Object: Values are passed while creating the object.
• Display Attributes: The stored values are accessed through the object.