Скачать или смотреть Creating an Immutable and Finite Data Type in Python: The Power of __new__

Learn how to implement an efficient Python class that represents different piano pitches while ensuring immutability and finite instances using the `__new__` method.
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This video is based on the question https://stackoverflow.com/q/64400596/ asked by the user 'Kenny' ( https://stackoverflow.com/u/14466892/ ) and on the answer https://stackoverflow.com/a/64401172/ provided by the user 'trincot' ( https://stackoverflow.com/u/5459839/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Creating an Immutable and Finite Data Type in Python: The Power of _new_

Have you ever faced challenges in ensuring the uniqueness and efficiency of objects in your Python code? This is a common issue, especially when dealing with a limited set of values such as musical pitches on a piano. In this guide, I’ll walk you through the process of creating a class that represents piano pitches and how to leverage the _new_ method to ensure immutability and finite instances of that class.

The Challenge: Representing Piano Pitches

Let’s set the scene. You are developing a music application where you need to work with different pitches that can be played on a piano. Since there are only 88 unique pitches, it’s essential to ensure:

Efficiency: Objects representing the same pitch should be the same instance.

Immutability: Once a pitch is created, it should not change.

You initially attempted to implement this with the _new_ method, but encountered an error related to the _init_ method not being correctly defined. Let’s address this error and discover a better way to structure your class.

Understanding the Solution

Using _new_ and _init_ Properly

The solution lies in understanding how the _new_ and _init_ methods work together. The _new_ method is responsible for creating a new instance of the class, while the _init_ method initializes the instance. Here’s how to correctly implement this:

Manage Instance Creation with __new__: Use this method to check if an instance of a specific pitch already exists. If it does, return that instance. If not, create a new one and store it.

Initialize Properties with _init__: After creating or retrieving the instance through __new__, use __init_ to set up the pitch value.

Code Implementation

Below is the correctly implemented Pitch class:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code

Class Variable: __pitches is a dictionary that stores existing instances of the class.

_new_ method:

Checks if the pitch value already exists in __pitches.

If it does not exist, it creates a new instance using super().__new__(cls) and stores it in the dictionary.

Always returns the instance from the dictionary.

_init_ method: Initializes the instance with the provided pitch value. This is where you use the value parameter effectively without producing warnings.

Example Usage

Now, let’s see how this class works in practice:

[[See Video to Reveal this Text or Code Snippet]]

In this example, we have two different pitch instances (A4 and A5), while dupe refers to the same instance as a4. This demonstrates both immutability and efficiency in action.

Conclusion

By utilizing the _new_ method to manage instances and the _init_ method to initialize them, you can create an elegant and efficient class in Python that represents an immutable and finite range of values. This approach not only optimizes your code but also enhances its readability and maintainability.

Feel free to adopt this pattern in your own projects, especially when dealing with similar finite value scenarios in Python!