Better Understanding Combobox in Tkinter - How to Get the Selected Value in Tkinter

Learn how to correctly handle the selected value from a combobox in Tkinter Python, understanding global variables and events in a clear, step-by-step guide.
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This video is based on the question https://stackoverflow.com/q/66474638/ asked by the user 'Kelevra' ( https://stackoverflow.com/u/13941797/ ) and on the answer https://stackoverflow.com/a/66476825/ provided by the user 'TheLizzard' ( https://stackoverflow.com/u/11106801/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Better Understanding Combobox in Tkinter - How to Get the Selected Value in Tkinter

If you're embarking on a journey to learn Python, you might find yourself grappling with various components of its GUI library, Tkinter. A common task you may encounter is retrieving user selections from a Combobox. This post aims to clarify how to effectively handle the selected value from a combobox and address some common pitfalls when working with global variables in Python.

The Challenge at Hand

You might be trying to create a simple interface withTkinter where a user selects an option from a Combobox. You will want to capture that selection and manipulate it in your Python code. The question arises: why does the following code snippet work:

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

but not this one?

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

Additionally, you might find yourself encountering an UnboundLocalError, indicating that the variable list_1 is being referenced before it's assigned. Let's dissect this problem step by step.

Understanding Variables and Scope

Global vs Local Variables

The main issue here pertains to variable scope in Python—how and where variables are accessible. In the context of your Tkinter application, consider the following:

Global Variables: These are declared outside any function and can be accessed throughout the entire script.

Local Variables: These are declared within a function and can only be accessed within that function.

When using list_1, if you want to modify it inside a class method (like selected), you need to inform Python of its global status:

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

This tells Python that you intend to work with the global list_1 variable rather than a local one that doesn't exist yet.

The Solutions

To resolve the issue in your Tkinter application, here’s how you can effectively get the value from the Combobox:

1. Setting Up the Combobox

You need to properly bind your Combobox to an event and set the variable correctly. Here’s a revised setup:

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

2. Handling the Selection

In the selected method, modify your code to acknowledge that list_1 is a global variable. Here’s the improved method:

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

With this setup, selecting an option from the Combobox will set the global list_1 variable to the selected value.

3. Printing the Selected Value

When you want to use or print the value that has been selected, you can simply reference list_1 in another method:

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

Putting It All Together

Here is the complete and revised version of the code:

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

Conclusion

Getting the selected value from a Combobox in Tkinter doesn't have to be a confusing endeavor. By understanding the role of global variables and effectively structuring your code, you can easily capture user selections and utilize them dynamically in your applications. Happy coding!