Fix Plotly Chart Width Warning

Dec 27, 2025 by Alex Johnson 31 views

Plotly Chart Width Warning: Understanding the `st.plotly_chart` kwargs Issue

When developing interactive dashboards and data visualizations with Streamlit, you'll often encounter the need to precisely control the layout and appearance of your charts. The st.plotly_chart function is a powerful tool for integrating Plotly figures into your Streamlit applications. However, recent versions of Streamlit might present a confusing deprecation warning related to keyword arguments (kwargs), even when you're not explicitly passing any variable keyword arguments, but instead using documented parameters like width='content'. This article aims to demystify this warning, explain why it occurs, and guide you on how to resolve it, ensuring a smoother development experience.

The Nuance of `st.plotly_chart` and Deprecation Warnings

At its core, the st.plotly_chart function in Streamlit allows you to render Plotly figures within your web application. Plotly itself is a sophisticated charting library that supports a vast array of customization options. Streamlit aims to bridge the gap between these rich charting capabilities and the simplicity of app development. When you use st.plotly_chart(fig, width='content'), you are instructing Streamlit to automatically adjust the width of the chart to fit its container. This is a very common and useful feature, as it helps your visualizations adapt gracefully to different screen sizes and layouts.

The issue arises from a change in how Streamlit handles keyword arguments internally. To prepare for future updates and to encourage more structured configuration, Streamlit introduced a deprecation warning for variable keyword arguments being passed directly to st.plotly_chart. The intention behind this change was to steer developers towards using the config argument for passing Plotly-specific configurations, which is a more organized and future-proof approach. However, it appears that the implementation of this warning might be a bit too broad, triggering even when standard, documented arguments like width are used.

Specifically, the warning 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 being displayed. This is perplexing because width='content' is a direct argument of st.plotly_chart, not a variable keyword argument being passed through an arbitrary **kwargs.

This behavior suggests a potential oversight in the warning's logic. It might be incorrectly interpreting certain standard arguments as part of the kwargs that are intended to be deprecated. This can be a source of confusion and unnecessary noise in your application logs and developer console, potentially masking other genuine deprecation warnings or issues.

Understanding this warning is crucial for maintaining clean and efficient Streamlit code. While it might not break your application's functionality immediately, it's a sign that your code, while working, is not fully aligned with the library's future direction. Addressing it proactively will save you potential headaches down the line when those deprecated kwargs are eventually removed entirely.

Reproducing the Warning: A Clear Code Example

To illustrate the problem clearly, let's look at a simple yet effective code snippet that triggers this deprecation warning. This example uses the popular plotly.graph_objects to create a basic chart and then displays it using st.plotly_chart with the width='content' parameter.

import plotly.graph_objects as go
import streamlit as st

# Create a simple Plotly figure
fig = go.Figure()
fig.add_trace(go.Barpolar(r=[1], theta=[0], width=[120]))

# Update layout, setting specific width and height for the figure itself
# Note: These layout parameters are for the Plotly figure, not for st.plotly_chart directly
fig.update_layout(width=500, height=360)

# Display the Plotly chart using st.plotly_chart with width="content"
st.plotly_chart(fig, width="content")

When you run this code in a Streamlit application (specifically with versions where this warning is active, like Streamlit 1.50.0), you will observe the deprecation warning in your console or Streamlit's developer tools. The warning indicates that "Variable keyword arguments for st.plotly_chart have been deprecated..." This is despite width='content' being a documented and intended parameter for controlling the chart's display size within the Streamlit container.

Here's why this code triggers the warning:

Import necessary libraries: We import plotly.graph_objects for creating the chart and streamlit for the web application framework.
Create a Plotly figure: A basic go.Figure() is instantiated.
Add a trace: A go.Barpolar trace is added. The width=[120] here refers to the width of the bar in the polar chart, which is a Plotly-specific parameter for the trace itself.
Update layout: fig.update_layout(width=500, height=360) sets the dimensions of the Plotly figure. These dimensions are internal to the Plotly object and might not directly dictate the rendered size in Streamlit when other sizing parameters are used.
Display with st.plotly_chart: The crucial part is st.plotly_chart(fig, width='content'). Here, width='content' is a parameter passed to Streamlit's plotly_chart function, intended to make the chart responsive to its container's width. This is where the warning appears.

The Streamlit warning mechanism, in this specific case, seems to be catching the width='content' argument and misclassifying it as a general, variable keyword argument that is subject to deprecation. This happens because Streamlit's internal handling of arguments passed to st.plotly_chart might check for any extra keyword arguments beyond its core set, and width falls into this trap.

This reproducible example highlights a clear discrepancy between the expected behavior (no warning for documented parameters) and the current behavior (a warning is shown). It's a straightforward way to identify and confirm the issue when you encounter it in your own projects.

Steps to Reproduce (as per the original report):

While the code example above is sufficient, the original report indicated:

No response for specific steps, implying the code example itself is the primary method of reproduction.

This indicates that the issue is consistently reproducible with the provided Python script, emphasizing its nature as a software bug or an unintended consequence of a recent update.

Understanding the Expected vs. Current Behavior

Let's delve deeper into what you should see and what you are actually seeing when using st.plotly_chart with specific width parameters, and why this discrepancy matters.

The Expected Behavior: Seamless Integration

When Streamlit introduces new features or deprecates old ones, the documentation is usually updated to reflect these changes. In this scenario, the documentation for st.plotly_chart (or related components) would guide users on how to control chart dimensions. As mentioned in the original report, the expected behavior when migrating from older methods (like potentially using use_container_width or directly passing Plotly layout arguments for sizing) to the newer width argument is that using the documented width parameter should not result in a deprecation warning.

Specifically, passing width='content' is a well-defined parameter that tells Streamlit to make the Plotly chart fluidly adapt its width to the available space within its parent container. This is a common and desirable behavior for responsive web design. Therefore, the expectation is that Streamlit would recognize width='content' as a valid, intended parameter and handle it without issuing any deprecation notices related to general kwargs.

This expectation is based on the principle of least surprise: users should not be warned about using features as documented. If a parameter like width is exposed and documented, it should be treated as a first-class argument, not something that triggers a generic kwargs deprecation warning.

The Current Behavior: The Puzzling `kwargs` Warning

The problem, as described, is that the very act of using width='content' (or potentially height='content') with st.plotly_chart is triggering a deprecation warning. The warning message explicitly states: "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 is problematic for several reasons:

Misleading: It suggests that the user is employing arbitrary, undefined keyword arguments. However, width is a specific, documented parameter.
Unnecessary Noise: It clutters the console output, making it harder to spot other, potentially more critical warnings or errors.
Potential Future Breakage: While not a current functional bug, it indicates that the way width is handled might be subject to change or could be perceived as a misuse that will break in the future if the warning is a harbinger of deprecation for this specific argument's usage.

The underlying cause, as hinted at in the provided context, seems to stem from Streamlit's internal argument parsing. A piece of code designed to catch and warn about truly variable keyword arguments (**kwargs) might be incorrectly intercepting the width parameter. This could be due to how width is passed down the call stack or how Streamlit's argument processing is structured.

Is This a Regression?

Yes, according to the provided information, this is a regression. This means the behavior was different in a previous version of Streamlit, where using st.plotly_chart with a width parameter like 'content' did not produce this deprecation warning. This suggests that a recent update to Streamlit, likely related to how it handles kwargs or specific plotting parameters, has inadvertently introduced this issue.

Regressions are particularly frustrating for developers as they can disrupt existing, working codebases with unexpected warnings or behavior changes. Identifying it as a regression helps pinpoint the problematic update and emphasizes the need for a fix to restore previous, stable functionality.

Debugging Information and Potential Solutions

To effectively address the st.plotly_chart kwargs deprecation warning when using the width parameter, it's helpful to have the specific details of the environment where the issue is observed. This information aids in diagnosing the exact cause and testing potential fixes.

Provided Debug Information:

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

This information is valuable. For instance, knowing the Streamlit version is critical, as this warning is likely tied to changes introduced around that version. The Python version and OS can sometimes reveal environment-specific quirks, though for a library like Streamlit, issues are often more general.

Underlying Cause Revisited

As previously discussed, the warning likely stems from Streamlit's internal argument handling. The code block responsible for issuing the warning looks something like this:

if kwargs:
    show_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."
    )

The core of the problem is that the width='content' argument, which is a valid and documented parameter for st.plotly_chart, is being caught by this if kwargs: check. This suggests that width is being passed into the kwargs collection within Streamlit's function signature, even though it's a recognized, named parameter.

Potential Solutions and Workarounds

Given that this appears to be a regression and an unintended behavior, the most robust solution would be for the Streamlit maintainers to adjust the warning logic. However, while waiting for an official fix, here are a few strategies you can employ:

Ignore the Warning (Temporarily): If the warning doesn't affect the functionality of your application, you might choose to ignore it for the time being. However, this is not a long-term solution, as deprecated features can be removed in future updates, potentially breaking your app.
Use the config Argument (if applicable): The warning itself suggests using the config argument. While width is not typically configured via Plotly's config object directly (it's more for things like scrollZoom, displayModeBar, etc.), you might explore if there's an indirect way Plotly's config can influence layout. However, for controlling the Streamlit container's width, width='content' is the intended parameter.
Explicitly Remove width from kwargs (Advanced/Internal): If you have access to modify Streamlit's source code or are developing a custom component, you would adjust the function signature or the warning logic to exclude known, documented parameters like width from the kwargs check. For end-users, this isn't a viable solution.
Downgrade Streamlit (Temporary Workaround): As this is a regression, downgrading to a previous Streamlit version where this warning did not occur would resolve the issue. For example, a version prior to 1.50.0 might work. However, this means missing out on newer features and bug fixes.
Check for Updates: Keep an eye on the Streamlit GitHub repository for issues tagged with plotly-chart and deprecation-warning. A fix might be in progress. Updating to the latest patch version of Streamlit once available should resolve this.

Recommended Approach:

Report the issue: If you haven't already, reporting this specific behavior on the Streamlit GitHub issues page (as was done in the original context) is the best way to ensure it gets addressed by the developers.
Use documented parameters: Continue to use documented parameters like width='content'. Once the issue is fixed, it will work as expected without warnings.

External Resources for Further Information:

For more insights into Streamlit's capabilities and troubleshooting common issues, consider exploring the following resources:

Streamlit Documentation: For official guides and API references, visit the Streamlit Official Documentation. It's the definitive source for understanding Streamlit's features and best practices.
Plotly Documentation: To understand Plotly's extensive customization options, refer to the Plotly Python Documentation. This will help you better leverage Plotly figures within Streamlit.
Streamlit GitHub Repository: For tracking issues, contributing to discussions, and staying updated on the latest developments, the Streamlit GitHub is an invaluable resource. You can often find active discussions about bugs and feature requests here.

By understanding the root cause and following these recommendations, you can navigate this st.plotly_chart deprecation warning effectively and maintain a robust Streamlit application.