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

__new__() controls the actual creation of an object before __init__() initializes it. It is rarely needed in everyday Python programming, but it is useful when creating immutable objects, implementing singleton patterns, or controlling which instance gets created.

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__

__init__ vs __new__

Types of Constructors

1. Default Constructor: does not take any parameters other than self. It initializes the object with default attribute values.

class Car:
    def __init__(self):

        self.make = "Toyota"
        self.model = "Corolla"
        self.year = 2020

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: accepts arguments to initialize the object's attributes with specific values.

class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year

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.