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Learn how to dynamically adjust the style of an `html.Img()` component in a Plotly Dash callback to display different images effectively.
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How to Change html.Img() Style in a Plotly Dash Callback

If you’re working with Dash—a productive framework for building web applications in Python—then you might have encountered situations where you need to dynamically change UI components based on user interaction or other events. A common challenge is modifying the properties of an image displayed using html.Img(), particularly adjusting its style within a callback function. In this post, we’ll explore how you can achieve this efficiently.

Understanding the Problem

Imagine you have an image component defined in your Dash app using the html.Img() function like so:

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

This component displays an image, but what if you want to change its size or other attributes dynamically based on user commands or inputs? You might think of altering the style of the image directly in a callback. This is a common request, and it can be done easily!

Solution Overview

Modifying the Callback

To adjust the style of your html.Img() component within a Dash callback, you need to specify style as an output in the callback’s decorator. Here’s how to do it step by step:

Use the Correct Output: In your callback definition, add an output for style. This will allow you to change the style property dynamically.

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

Return the New Style: After calculating the new source for the image, create a new style dictionary that reflects the desired properties for your image.

Implementing the Callback Function: In your callback function, return both the new image source and the new style.

Example of Implementation

Here’s an illustrative implementation based on your original question:

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

Alternative Approach: Wrapping in a Div

If you find that you need to change multiple attributes together or swap images frequently, consider wrapping your html.Img() component within a div. Update the children property of the div to switch images:

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

Conclusion

With these techniques, you can easily modify the html.Img() component's style attributes in response to various user inputs or interactions within your Dash applications. Whether you opt to change the style directly or wrap your image in a div, Dash provides a flexible way to create dynamic and responsive user interfaces.

Now you have all the tools you need to make your images adaptive to the context of your application—happy coding!