Скачать или смотреть How to Fix AttributeError When Accessing Class Variables in Python

Discover how to resolve the `AttributeError` in Python when trying to access instance variables from a class. This guide will help you understand the object-oriented programming concept better.
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This video is based on the question https://stackoverflow.com/q/62234870/ asked by the user 'ertemo' ( https://stackoverflow.com/u/13082302/ ) and on the answer https://stackoverflow.com/a/62235050/ provided by the user 'James' ( https://stackoverflow.com/u/13155314/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

When working with classes in Python, one common issue developers encounter is the inability to access variables that are initialized within the class itself. In the case you’re facing, you’ve created a custom Window class that should allow you to access its instance variables, but you get an error stating that the object has no such attribute.

This type of error, known as AttributeError, indicates that the program is trying to access an attribute that doesn’t actually exist on the object. Let's take a look at the code snippet you provided and understand what’s going wrong.

The Code Snippet

Here’s the code snippet in question:

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

In this code, you’ve defined your custom Window class which inherits from pyglet.window.Window. Inside the _init_ method, you've defined two instance variables: self.renderer and self.test. However, when you create an instance of your Window class using pyglet.window.Window, you are not creating an instance of your custom class, but instead of the pyglet class itself.

The Root Cause of the Issue

The main reason you're encountering this issue is that when you run:

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

You are creating an instance of the Window class from the pyglet library, not your custom Window class. Hence, when you try to access window.test, Python throws an AttributeError because the pyglet Window object does not have the test attribute defined in your custom class.

The Solution

To fix the issue, you need to create an instance of your custom Window class instead of the pyglet one. Here’s how you can do it:

Change Instance Creation: Modify the instance creation line to refer to your custom Window class.

Replace:

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

With:

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

Verify the Changes: After making this change, you should be able to access window.renderer and window.test without any issues.

The complete corrected code will look like this:

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

Conclusion

By ensuring you instantiate your custom class instead of the library's class, you can access your defined attributes without encountering AttributeError. This small yet significant change makes all the difference in your object-oriented programming endeavors in Python. Happy coding!