Why is Python's `__init__()` method always called after `__new__()`?

Understanding the Sequence of __new__() and __init__() Methods

In Python, when creating an object, two essential methods come into play: __new__() and __init__(). While __init__() is commonly associated with object initialization, __new__() plays a fundamental role in creating a new instance of the class.

Why is __init__() Always Called After __new__()?

The reason __init__() is always invoked after __new__() stems from the class object instantiation process. When creating a new object of a class, Python first executes the __new__() method. This method is responsible for allocating memory, creating the new instance, and returning it.

Once the __new__() method successfully creates the new instance, Python proceeds to call the __init__() method. The __init__() method, as the name suggests, is used to initialize the new instance by setting its attributes and executing any necessary setup code.

An Example of __new__() and __init__() Interactions

Consider the following Python code:

class Singleton:
    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super(Singleton, cls).__new__(cls)
        return cls._instance

    def __init__(self):
        # Instance-specific initialization code

In this example, the Singleton class implements a singleton design pattern using __new__(). The __new__() method checks if an instance already exists and returns it if so. Otherwise, it creates a new instance using the super() method and assigns it to the _instance attribute.

The __init__() method is then called to initialize the newly created instance. In this case, it can be used to set additional attributes or perform any other necessary setup.

Alternatives to Using __new__()

While __new__() provides flexibility in controlling instance creation, it's generally not recommended for general-purpose code. One alternative is the Factory pattern, which allows you to create objects without exposing the underlying creation logic.

Conclusion

In summary, __new__() and __init__() play distinct roles in the object instantiation process in Python. __new__() handles the creation of the new instance, while __init__() initializes it. Understanding the interplay between these methods is essential for designing and implementing robust object-oriented code.

The above is the detailed content of Why is Python's `__init__()` method always called after `__new__()`?. For more information, please follow other related articles on the PHP Chinese website!