How to Dynamically Add Property Accessors in Python Using getattr

Описание: Discover how to create class properties in Python programmatically, without repeating code for new entries, using the power of `getattr`.
---
This video is based on the question https://stackoverflow.com/q/63947677/ asked by the user 'jlee' ( https://stackoverflow.com/u/8254487/ ) and on the answer https://stackoverflow.com/a/63948337/ provided by the user 'terehpp' ( https://stackoverflow.com/u/14154287/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Python - how to add property accessors programmatically

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mastering Dynamic Property Accessors in Python

Creating dynamic class properties can be a daunting task if you're doing it manually every single time you need a new entry. Fortunately, Python provides several powerful features that allow developers to handle this with ease. In this post, we’ll look at how to programmatically add property accessors using getattr and a creative implementation for your class.

The Challenge

Suppose you're designing a class, and you have a list of items for which you want to create properties dynamically. For example, you want to create properties itemA, itemB, and eventually add more items as your application grows. Instead of adding @ property decorators and methods for each new item — which can quickly become tedious — you want a more scalable solution.

Here’s what you might start with:

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

However, this code leads you to a rather frustrating outcome: when you try to access itemA, you get a property object instead of its actual value.

The Solution: Using getattr

Overview of getattr

Instead of manually defining each property, you can leverage the magic method __getattr__. This allows you to encapsulate the logic to retrieve attributes dynamically. Here’s how you can do this:

Step-by-Step Implementation

Define the class: Start by defining your class and initializing the items list.

Implement __getattr__: Override this method to handle access to properties that do not exist on the instance.

Fetch values: In __getattr__, call a method that will retrieve or compute the value you need.

Example Code

Here’s how this can be implemented in Python:

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

Explanation of the Code

_init_ method initializes items containing property names.

_getattr_ checks if the requested attribute name exists in the items list.

If it does, it calls the internal method __get_method(name) to fetch the value.

If not, it raises an AttributeError, which is a good practice to notify the user of an invalid attribute access.

__get_method is a placeholder for your logic to retrieve the actual value.

Benefits of Using getattr

Scalability: Easily add new items—just update the items list.

Clean Code: Avoid bloating your class with multiple property definitions.

Dynamic Control: Access to complex logic can be handled gracefully.

Conclusion

Using getattr to dynamically create property accessors in Python is not just efficient, but it also helps you write clearer, more Maintainable code. Whenever you find yourself repeating property definitions in a class, consider leveraging this technique for a more elegant solution.

With these strategies, you'll save time, enhance your code organization, and provide future-proofing as your application expands—allowing your code to adapt just as easily as the items you need to manage.