__init__ vs __new__ in Python – The Real Constructor Debate!

Hi Pythonistas!,

If you think __init__ is Python’s constructor, think again!. Python’s real constructor is __new__, not __init__.Let’s clear up the confusion!

__new__ – The Actual Constructor
Creates the object (allocates memory).
Runs before __init__.
Returns the newly created instance.
Used for Singletons, Immutable objects, and Metaclasses.
Example of __new__ Alone

class Example:
    def __new__(cls):
        print("Inside __new__")
        instance = super().__new__(cls)  # Create the object
        return instance  

obj = Example()  

Output

Inside __new__

✅ No __init__, but object still gets created!

__init__ – Just an Initializer
Does NOT create the object.
Runs after __new__.
Only initializes attributes of an already existing object.
Example of __init__ Alone

class Example:
    def __init__(self):
        print("Inside __init__")
        self.value = 42  # Initialize attributes  

obj = Example()  

Output:

Inside __init__

✅ Object was already created before __init__ ran.

How __new__ and __init__ Work Together

class Example:
    def __new__(cls):
        print("Inside __new__")
        instance = super().__new__(cls)
        return instance  

    def __init__(self):
        print("Inside __init__")
        self.value = 42  

obj = Example()

Output:

Inside __new__

Inside __init__

✅ First, __new__ creates the object. Then, __init__ initializes it.

When Should You Use __new__?
Use __new__ when you need control over object creation, such as:

• Singleton Pattern (only one instance should exist)
• Immutable Objects (like tuple, str)
• Metaclasses (custom class creation behavior)

Key Differences at a Glance

Feature	__new__ (Constructor)	__init__ (Initializer)
Purpose	Creates the object	Initializes the object
When does it run?	Before object is created	After object is created
Return Type	Must return an instance of the class	Returns nothing (None)
Use case	Singleton, Metaclasses, Immutable Objects	Normal object initialization

__new__ is the real constructor in Python, while __init__ just sets up the object. Please share your valuable suggestions with afsal@parseltongue.co.in