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Discover how to create a Python method that accepts variable names as arguments and modifies instance variables in place for dynamic class manipulation.
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This video is based on the question https://stackoverflow.com/q/62559684/ asked by the user 'VicN' ( https://stackoverflow.com/u/13640470/ ) and on the answer https://stackoverflow.com/a/62560141/ provided by the user 'Roy2012' ( https://stackoverflow.com/u/1105560/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Create a Method that Modifies Instance Variables in Python Classes

When working with classes in Python, you might encounter a situation where you want to create a method that can modify instance variables dynamically based on given input. This flexibility can be particularly useful in various programming scenarios, especially when you have multiple variables and want to work with them generically.

In this post, we will explore how to create such a method that can take the name of an instance variable and modify its value effectively.

Understanding the Problem

Let's start with the example provided. You have a class called classTest with two instance variables: a and b. You want to create a method called addN that takes an instance variable (like a or b) and adds a specified number to it. However, the initial attempt does not achieve the desired functionality.

Here’s the initial class structure:

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

When you try calling addN:

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

The output remains unchanged:

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

Creating the Solution

To effectively modify an instance variable using a method, we can use the getattr() and setattr() functions. These built-in functions allow us to access and modify attributes of an object dynamically using their names as strings.

Here’s how we can structure the updated method:

Step 1: Define the new method

Modify your addN method to accept the name of the instance variable as a string and the number to be added. The key changes are:

Use getattr(self, var_name) to retrieve the current value of the instance variable.

Use setattr(self, var_name, new_value) to update the instance variable with the new value.

Updated Code

Here’s the complete class with the required modifications:

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

Conclusion

With this approach, you can now easily modify any instance variable in your class without needing to write separate methods for each variable. The use of getattr() and setattr() functions gives your code a flexible design, allowing you to dynamically interact with your class attributes.

Feel free to adapt this strategy to suit your programming needs, and enjoy the power of dynamic variable handling in Python!