Streamlit Plotly Chart Width Warning

by Alex Johnson 37 views

When you're building interactive dashboards and data visualizations with Streamlit, you want things to just work. You spend time crafting your plots using libraries like Plotly, and then you integrate them seamlessly into your Streamlit app. Recently, some users have encountered a puzzling situation: a deprecation warning related to kwargs when using st.plotly_chart with the width="content" parameter, even when they weren't explicitly passing any variable keyword arguments. This can be a bit frustrating, as it suggests an issue that might not actually exist in your code.

Let's break down why this warning appears, what it means, and what you can expect. We'll explore the current behavior, the expected behavior, and how this might be a regression for some users. Understanding this will help you navigate these warnings more effectively and ensure your Streamlit applications run smoothly.

Understanding the st.plotly_chart Deprecation Warning

The core of the issue lies in how Streamlit handles arguments passed to its components, particularly st.plotly_chart. This component is designed to render Plotly figures within your Streamlit app. Plotly itself is a powerful library that allows for a great deal of customization through various arguments and configurations.

Streamlit, in its continuous effort to improve and streamline its API, sometimes deprecates older ways of doing things in favor of newer, more robust methods. In this case, the warning specifically mentions kwargs (keyword arguments). The message, "Variable keyword arguments for st.plotly_chart have been deprecated and will be removed in a future release. Use the config argument instead to specify Plotly configuration options," is a clear signal that the way certain Plotly-specific settings were being passed might be changing.

However, the confusion arises because this warning is triggered even when you're not using arbitrary kwargs. You might be using documented parameters like width="content" or height which are intended to control the dimensions of your Plotly chart within the Streamlit layout. The warning suggests that even these standard parameters are being caught by the kwargs check, leading to an unnecessary alert.

The Role of width="content"

The width="content" parameter is particularly useful. It tells Streamlit to automatically adjust the width of the Plotly chart to fit the available space within its container. This is fantastic for responsive design, ensuring your charts look good on different screen sizes without manual adjustments. When you set width="content", you're not passing a generic keyword argument; you're using a specific, documented feature designed to enhance the user experience.

The problem is that the internal implementation of st.plotly_chart might be interpreting these dimension-related arguments in a way that triggers the kwargs deprecation warning. This could be due to how the arguments are processed internally before being passed to the underlying Plotly rendering engine. Even though you're using the API as intended, the warning appears, which can be misleading.

Why is this a Concern?

  • Misleading Information: Developers might spend time trying to hunt down non-existent kwargs in their code, believing they've used the API incorrectly. This wastes valuable debugging time.
  • API Clarity: Warnings should accurately reflect a problem with the user's code. When a warning appears for valid usage, it undermines confidence in the API's documentation and error reporting.
  • Potential for Future Breakage: While the warning is about deprecation, it hints that the current mechanism for handling arguments like width might be subject to change, which could impact applications in future updates.

Let's look at a practical example to illustrate this.

Reproducible Code Example and Observed Behavior

To pinpoint the issue, a clear, reproducible code example is crucial. Consider this simple Streamlit script:

import plotly.graph_objects as go
import streamlit as st

fig = go.Figure()
fig.add_trace(go.Barpolar(r=[1], theta=[0], width=[120]))
fig.update_layout(width=500, height=360)

st.plotly_chart(fig, width="content")

In this code, we create a basic Plotly figure and then display it using st.plotly_chart. The key part here is width="content". According to Streamlit's documentation, this should be a valid way to control the chart's width. However, when you run this code with certain versions of Streamlit (specifically mentioned as 1.50.0 in the report), you'll likely see the following deprecation warning:

Variable keyword arguments for st.plotly_chart have been deprecated and will be removed in a future release. Use the config argument instead to specify Plotly configuration options.

This warning appears despite the fact that we are only using documented parameters and not passing any arbitrary kwargs to the st.plotly_chart function.

Analyzing the Current Behavior

The warning message itself provides a clue: if kwargs:. This suggests that Streamlit's internal logic checks if there are any remaining keyword arguments after it has processed its own known parameters. If there are, it triggers the warning.

In the context of st.plotly_chart(fig, width="content"), it seems that the width argument, even though documented, might be processed in a way that leads to this kwargs check. It's possible that Streamlit is passing width="content" through a mechanism that makes it appear as an unrecognized keyword argument to the internal kwargs check.

This behavior is particularly problematic because it doesn't align with the expected functionality described in the Streamlit documentation. Users are led to believe that width="content" is a supported and recommended way to manage chart dimensions, but the warning suggests otherwise.

Expected Behavior

The expected behavior, based on Streamlit's documentation and the general intent of such parameters, is that using documented arguments like width="content" should not trigger a deprecation warning related to variable keyword arguments. If width is a valid parameter for st.plotly_chart, it should be handled gracefully without invoking the kwargs warning.

The ideal scenario is that the deprecation warning is reserved only for instances where users are truly passing unrecognized keyword arguments that are not part of the function's defined signature or special handling mechanisms like the config dictionary.

When the width parameter is used correctly, the chart should render with its width adjusted to the content, and no deprecation warnings should appear. This ensures a clean and informative developer experience, where warnings accurately guide users towards best practices or potential issues, rather than flagging correct usage.

Is This a Regression?

Yes, the issue described appears to be a regression. The report explicitly states, "This used to work in a previous version." This is a critical piece of information. Regressions occur when a feature that previously functioned correctly begins to behave unexpectedly or throws errors/warnings in a newer version of the software.

What Does a Regression Mean Here?

In this context, a regression means that in an earlier version of Streamlit, using st.plotly_chart with width="content" (or potentially other dimension-related arguments) did not trigger the kwargs deprecation warning. Developers could rely on this functionality without receiving confusing alerts.

The introduction of this warning in newer versions (like 1.50.0) indicates a change in Streamlit's internal argument handling or warning logic. While the intention behind the deprecation of arbitrary kwargs is likely to enforce better API usage and prepare for future changes, the side effect of this change is that it's now incorrectly flagging a valid and documented use case.

Impact of Regressions

Regressions can be disruptive to development workflows for several reasons:

  1. Undermining Confidence: When previously stable features start producing warnings, developers may become hesitant to update their Streamlit versions, fearing other unintended consequences.
  2. Increased Debugging Time: As mentioned earlier, developers might spend time debugging code that isn't actually broken, simply because of an inaccurate warning.
  3. Maintenance Challenges: If the issue isn't addressed, applications might be stuck on older Streamlit versions, missing out on new features, performance improvements, and security updates.

The fact that this is a regression highlights the importance of thorough testing during software updates. Changes intended to clean up API usage should be carefully implemented to avoid breaking existing, valid patterns.

Debugging Information and Next Steps

The provided debug information gives us specific details about the environment where this issue was observed:

  • Streamlit version: 1.50.0
  • Python version: 3.14.2
  • Operating System: MacOs 26.1
  • Browser: Chrome

This information is invaluable for Streamlit developers to reproduce and diagnose the problem. It pinpoints the exact software versions involved, which is crucial because API behavior can change significantly between versions.

What Can You Do?

  1. Verify the Warning: If you encounter this warning, double-check your st.plotly_chart calls. Ensure you are only using documented parameters like width, height, use_container_width, or the config dictionary for Plotly settings. Avoid passing other arbitrary keyword arguments.
  2. Check Streamlit Version: If you are on Streamlit version 1.50.0 or a similar version where this issue is known, consider if updating to the latest stable version of Streamlit might resolve the problem. Often, such regressions are identified and fixed in subsequent releases.
  3. Use the config Argument: As the warning suggests, for Plotly-specific configurations, the config argument is the recommended approach. While width="content" is a Streamlit parameter, other Plotly configurations should ideally be passed via config. If width itself is the issue, and updating doesn't help, you might need to explore alternative ways to control width if they exist or stick to older versions where it worked.
  4. Report the Issue: If you've confirmed this is a regression and occurs even with documented parameters on the latest Streamlit version, consider reporting it officially. Providing the reproducible code example and the debug information (as done in the original report) is the best way to help the Streamlit maintainers address the bug.

Looking Ahead

The Streamlit team is actively working on improving the library. Understanding these warnings and reporting issues like this helps them refine the API and ensure a better experience for everyone. The goal is to make Streamlit a powerful, intuitive, and reliable tool for building data applications.

For more insights into Streamlit's features and best practices, you can always refer to the official documentation. If you're interested in the intricacies of Plotly and how to best integrate it with web frameworks, exploring the Plotly documentation can provide valuable context and advanced configuration options.

By staying informed and contributing feedback, we can all help shape the future of Streamlit development.