Python Object Creation: __new__ vs __init__

Python’s magic methods __new__ and __init__ play complementary roles in the lifecycle of an object:

πŸ‘‰ __new__ is a static method, primarily concerned with creating and returning a new instance of a class; it acts before the object is fully instantiated in memory.

πŸ‘‰ Following this, __init__ functions as an instance method, tasked with configuring the specific attributes of the newly minted object, thus defining its initial state.

This orchestrated sequence ensures that the structural foundation established by __new__ precedes the customization of the object’s properties through __init__.

This design provides a clear and methodical approach to object creation and initialization in Python.

Minimal Example

Here’s a simple example that demonstrates the difference between __new__ and __init__ in Python:

class MyClass:
    def __new__(cls):
        print("Creating instance")
        return super(MyClass, cls).__new__(cls)

    def __init__(self):
        print("Initializing instance")

# Creating an object of MyClass
obj = MyClass()

In this example:

  • When MyClass() is invoked, __new__ is called first. It is responsible for creating and returning a new instance of the class. Here, it prints “Creating instance” and uses super() to call the __new__ method of the superclass to allocate the memory for the new object.
  • Once the new instance is created and returned by __new__, __init__ is called to initialize the new object. In this case, it prints “Initializing instance”.

This output illustrates the order and roles of __new__ and __init__ in Python’s object creation process.

FAQ: Understanding __new__ and __init__ in Python

1. What is the purpose of __new__ in Python?

__new__ is a static method responsible for creating a new instance of a class. It is the first step in the instance creation process, handling memory allocation before any attributes are initialized.

2. How does __init__ differ from __new__?

While __new__ creates the instance, __init__ is tasked with initializing the newly created object’s attributes. It sets up the initial state of the object after __new__ has already created it.

3. When would you need to override __new__ instead of __init__?

Overriding __new__ is less common but is necessary when you need to control the creation of a new instance, such as enforcing certain patterns (like singletons), modifying immutable types, or extending immutable types like tuples and strings.

4. Can __init__ return a value?

No, __init__ should not return anything except None. It is designed purely for initialization and not for creating new instances, which is the role of __new__.

5. What happens if __new__ does not return an instance of the class?

If __new__ returns something that isn’t an instance of the class in which it’s defined, then __init__ will not be called. This can be used intentionally to control the type of objects your class creates or returns.

6. Is it mandatory to call the base class’s __new__ when overriding it?

Yes, generally you should call the base class’s __new__ using super() to ensure that the object gets properly created before you attempt to initialize it in __init__.

7. Can __init__ be called multiple times on the same instance?

Yes, __init__ can technically be called multiple times for the same instance, allowing reinitialization of the object. However, __new__ is typically called only once per object creation.

8. Are __new__ and __init__ only relevant to classes defined in Python code?

__new__ and __init__ are relevant for any class, including those from Python’s standard library or third-party libraries that follow the object-oriented paradigm.

πŸ‘‰ Understanding the Differences Between self and init Methods in Python Classes