Скачать или смотреть Using a Class Variable Across Inheritance in Python

Learn how to effectively use class variables in a parent-child class structure in Python, allowing child classes to inherit and modify class-level variables seamlessly.
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This video is based on the question https://stackoverflow.com/q/75403349/ asked by the user 'Santiago Cuellar' ( https://stackoverflow.com/u/13382982/ ) and on the answer https://stackoverflow.com/a/75403499/ provided by the user 'Nick Goldstein' ( https://stackoverflow.com/u/17828745/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Using a Class Variable Across Inheritance in Python: A Simple Guide

Inheritance is a powerful feature of object-oriented programming that helps in sharing functionality. However, utilizing class variables across inherited classes can sometimes lead to confusion, particularly when you want to modify those variables at different levels. In this guide, we'll explore how to correctly implement class variables in a parent-child relationship in Python.

The Problem: Class Variables and Inheritance

You may find yourself in a situation where you'd like to define a variable at the class level in a parent class. Ideally, when you create child classes that inherit from this parent, they should be able to change this variable while still accessing the parent class's functionalities. However, this can be tricky when your child class attempts to redefine that variable.

Example Scenario

Consider the following simplified example where you have a Parent class and a Child class:

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

If you run this code, you'll get the following output:

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

You might expect the output for the child class to display "child", but instead, it still prints "parent". This is not what we want!

The Solution: Using self to Access Class Variables

The solution lies in changing how we access the class variable within the printmg method. Instead of referencing Parent.my_global, we can use self.my_global. This way, Python will look for my_global in the context of the current instance of the class (whether it’s from Parent or Child).

Here’s how you can modify your code:

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

Why This Works

Understanding self: The self keyword refers to the current instance of the class. By using self.my_global, you instruct Python to look for my_global in the class of the current object.

Accessing Class Variables: When my_parent.printmg() is called, self refers to the instance of Parent and uses Parent.my_global. Conversely, when my_child.printmg() is invoked, self refers to the Child instance, which recognizes my_global defined in Child.

Conclusion

By making a simple adjustment to how we access class variables, we can smoothly inherit and modify class-level variables in Python. This enables greater flexibility in our code structure and functionality, especially in classes that share similar characteristics.

With this understanding, you’re now equipped to utilize class variables effectively across inheritance in Python! Happy coding!