Python’s __new__() Method Explained

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” every time you see it but secretly love it for its mysterious powers: __new__(). ️

So Let’s begin exploring with this magical land of object creation and unravel the secrets behind Python’s __new__() method. But first, a little background story…

In Python, when you create an instance of a class using `my_obj = MyClass()`, what actually happens is that Python calls two methods: `__new__(cls)` and `__init__(self)`.

The `__new__()` method is called first, and it’s responsible for creating a new object. It takes one argument the class itself (which we call “cls” in Python). The purpose of this method is to give you complete control over how objects are created from your classes.

But why would anyone want that kind of power? Well, let’s say you have a class for creating custom database connections, and you want to make sure that each connection object has unique properties based on the user who is using it. You can use `__new__()` to create an instance with those specific properties before calling `__init__(self)`.

Here’s how:

# Creating a class for custom database connections
class MyDatabaseConnection(object):
    # Using __new__() to create an instance with specific properties before calling __init__()
    def __new__(cls, user_id):
        # Check if the connection already exists for this user ID. If it does, return that object instead of creating a new one.
        # Using cls.connections to access the dictionary of existing connections
        existing = cls.connections.get(user_id)
        if existing:
            # If the connection already exists, return it
            return existing
        else:
            # Otherwise, create a new connection and add it to the dictionary for future use
            obj = super().__new__(cls)
            # Using connect() to establish a connection with the database using the user ID
            obj.connection = connect(f"dbname={user_id}")
            # Adding the new connection to the dictionary using the user ID as the key
            cls.connections[user_id] = obj
            # Returning the new connection object
            return obj
    
    # Initializing the connection object with additional properties
    def __init__(self, user_id):
        # Using the user ID as a property of the connection object
        self.user_id = user_id
    
    # Creating a dictionary to store all the connections
    connections = {}

In this example, we’re using `super()` to call the parent class’s implementation of `__new__(cls)`. This is important because it ensures that our custom implementation doesn’t break any existing functionality.

Now some best practices for using __new__. First, always remember that you should use this method sparingly and only when necessary. It can be tempting to overuse `__new__()` in order to add fancy features or optimize performance, but it’s not worth the headache if you don’t really need it.

Second, always document your use of __new__. This is especially important if you’re working on a team project and other developers might be confused by what you’ve done. Make sure to explain why you used `__new__()` instead of the more common `__init__(self)`, and how it affects the behavior of your class.

Finally, always test your use of __new__. This is especially important if you’re modifying existing functionality or adding new features that might break something else in your codebase. Make sure to run tests before and after making any changes, and make sure they pass!

And there you have it a brief introduction to Python’s __new__() method. Remember: use sparingly, document thoroughly, test rigorously!

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