__new__ vs. __init__ Methods in Python

When learning about object-oriented programming (OOP) in Python, you’ll come across the __new__ and  __init__ magic methods. These two methods play a vital role in the creation and initialization of objects in Python.

What Is the __new__ Method in Python?

The __new__ method is a static method that belongs to a class itself. It’s responsible for creating and returning a new instance (object) of the class.

The method takes the class as its first argument, followed by any additional arguments that need to be passed to it.

class MyClass:
    def __new__(cls, *args, **kwargs):
        instance = super().__new__(cls)
        return instance

The __new__ method is called before __init__ and is used to control the object creation process. Inside this method, a call to super().__new__(cls) is typically made. This step delegates the actual creation of the object’s memory to the parent class, ensuring the new instance is properly built before it’s returned.

What Is the __init__ Method in Python?

The __init__ method is an instance method that automatically initializes a newly created object. While it operates on an instance, it’s not called directly by the programmer, and is invoked automatically by Python after the __new__ method creates the object.

The method takes the object as its first argument (self), followed by any additional arguments that need to be passed to it.

class MyClass:
    def __init__(self, *args, **kwargs):
        self.attribute = 'value'

The __init__ method is called after an object is created by the __new__ method, and it initializes the object attributes with the values passed as arguments.

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Differences Between __new__ and __init__ in Python

• __init__ is an instance method, while __new__ is a static method.
• __new__ is responsible for creating and returning a new instance (object), while __init__ is responsible for initializing the attributes of the newly created object.
• __new__ is called before __init__.
• __new__ happens first, then __init__.
• __new__ can return any object, while __init__ must return None.

When to Use __new__ in Python

You should use __new__ when you need to customize the object creation process itself, before __init__ is even called. For example, you can use __new__ to:

• Ensure that the object is of a certain type.
• Set the object’s initial state (especially when working with immutable classes).
• Prevent the object from being created.

When to Use __init__ in Python

You should use __init__ when you need to initialize the object. For example, you might want to use __init__ to:

• Set the object’s attributes.
• Call the object’s superclass’ __init__ method.
• Perform other initialization tasks.

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Python __new__ and __init__ Example

To better understand the differences between __new__ and __init__, let’s take a look at a simple example:

class Person:
    def __new__(cls, name, age):
        print("Creating a new Person object")
        instance = super().__new__(cls)
        return instance

    def __init__(self, name, age):
        print("Initializing the Person object")
        self.name = name
        self.age = age

person = Person("John Doe", 30)
print(f"Person's name: {person.name}, age: {person.age}")

# Creating a new Person object
# Initializing the Person object
# Person's name: John Doe, age: 30

In this example, we can see how the __new__ method is called before the __init__ method, and how they work together to create and initialize the Person object.

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