Streamlit: Plotly Chart Width Deprecation Warning Fix

Hey there, data visualization enthusiasts! Have you ever been working on your Streamlit apps and noticed a pesky deprecation warning pop up when using st.plotly_chart, specifically when trying to set the width to "content"? You might be scratching your head, thinking, "But I'm not passing any extra keyword arguments!" Well, you're not alone, and we've got some insights into why this might be happening and what's expected.

The Sneaky Warning

It seems like there's a bit of a quirk in Streamlit's st.plotly_chart function. When you use the width="content" (or height="content") parameter, users are encountering a deprecation warning related to kwargs. This is happening even when they aren't explicitly passing any variable keyword arguments, and are only utilizing the documented parameters. This can be a bit confusing, as you're trying to follow the documentation, but still get a warning that suggests you're doing something wrong.

What's Happening Under the Hood?

The core of the issue seems to stem from how Streamlit handles internal arguments versus user-provided arguments. In recent updates, there was a change to how variable keyword arguments (kwargs) are managed within st.plotly_chart. The intention was to steer users towards using the config argument for Plotly-specific configurations, which is a cleaner approach. However, it appears that even when using a documented parameter like width="content", the underlying logic might be triggering this kwargs check, leading to the warning.

The problematic code snippet often cited is:

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."
 )

As you can see, this code is designed to warn if there are any kwargs present. The confusion arises because width="content" is a documented parameter for controlling the chart's size, but it might be getting caught in this broader kwargs check, leading to the deprecation warning.

This is particularly frustrating when you're trying to achieve a responsive layout, making your charts adapt to the available space. Using width="content" is a perfectly valid way to do this, and it's expected that such documented features wouldn't trigger warnings about deprecated practices.

It's a common scenario: you're building a dashboard, you want your plots to look good on different screen sizes, and you reach for the width="content" option. Then, bam, a deprecation warning appears. It makes you pause and reconsider, even though you haven't done anything that seems overtly wrong according to the official documentation. This suggests a small disconnect between the user-facing API and the internal implementation details.

The Expected Behavior

When you're updating your Streamlit applications, you'd naturally expect that using the width argument (as documented) would work seamlessly without raising deprecation warnings. The documentation clearly indicates that width="content" is a supported value for controlling the chart's display. Therefore, the expected behavior is that using this parameter should not result in a deprecation warning related to kwargs. The warning should only appear when users are passing truly variable or undocumented keyword arguments that are meant to be handled by the config parameter.

This means that Streamlit should intelligently distinguish between its own documented parameters (like width and height) and any other arbitrary kwargs that a user might pass. The deprecation warning is intended to guide developers towards the config argument for advanced Plotly settings, not to flag the use of standard Streamlit parameters that control chart dimensions.

In summary, the ideal scenario is:

• Use st.plotly_chart(fig, width="content").
• The chart displays correctly, adjusting its width to the content.
• No deprecation warnings appear related to kwargs.

This ensures a smooth developer experience and prevents unnecessary noise in the console logs, allowing developers to focus on building great applications rather than deciphering potentially misleading warnings.

Current Behavior: A Baffling Warning

Currently, however, developers are experiencing the opposite. When they implement the documented width="content" parameter, they are indeed seeing the kwargs deprecation warning. This implies that the logic checking for kwargs is perhaps too broad and is catching the width parameter as if it were an unhandled variable keyword argument. This is not just an inconvenience; it can be seen as a regression, especially if it worked without issue in previous versions of Streamlit.

Imagine you've just updated Streamlit to the latest version, excited about new features, only to find that a perfectly functional part of your code now throws a warning. It's the kind of thing that makes you wonder if you're missing something or if the update has introduced a bug. The warning message itself, suggesting the use of the config argument, further adds to the confusion because width is not a Plotly configuration option that belongs in config; it's a Streamlit-specific display parameter.

This situation can lead to a few undesirable outcomes:

1. Developer Confusion: Developers might spend time trying to understand why they're getting a warning, potentially trying to move width="content" into the config parameter (which won't work as intended) or trying to refactor their code unnecessarily.
2. Masking Real Issues: If the console is flooded with these false positive warnings, it becomes harder to spot actual deprecation warnings or other critical errors.
3. Perceived Instability: It can give the impression that the library is less stable or predictable than it is, even if the core functionality remains intact.

Is This a Regression?

Yes, this appears to be a regression. The fact that this functionality was working without warnings in a previous version of Streamlit and now triggers a deprecation warning strongly suggests that a recent change has introduced this behavior. Regressions are always a concern, as they can disrupt established workflows and introduce unexpected issues for users who have upgraded.

It highlights the importance of thorough testing, especially when refactoring internal argument handling. When changes are made to how arguments are processed, it's crucial to ensure that existing, documented functionalities continue to operate as expected and do not trigger unintended warnings. This specific issue seems to indicate that the internal check for kwargs might be too aggressive or not correctly excluding Streamlit's own display parameters.

Diving into the Code Example

Let's look at the reproducible code example provided:

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")

This code creates a simple Plotly figure and then displays it using st.plotly_chart. The key here is the width="content" argument passed to st.plotly_chart. According to the Streamlit documentation, this should instruct the chart to take up the available horizontal space within its container.

When this code is run with a recent version of Streamlit (like 1.50.0), the st.plotly_chart function executes. It prepares the Plotly figure and renders it. However, somewhere in its internal process, it encounters the width="content" argument. Instead of silently accepting it as a valid display parameter, the function's logic triggers the kwargs check. Since width is being passed and is not explicitly handled in a way that bypasses the kwargs warning mechanism, the deprecation warning is shown.

This is precisely why it's considered a regression: the behavior has changed. Previously, passing width="content" would simply work. Now, it brings along an unnecessary warning, suggesting that kwargs are being used improperly, when in fact, a documented parameter is being employed.

Debugging and Environment Details

To help pinpoint the issue, the following environment details were provided:

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

These details are crucial for developers to reproduce the bug and for the Streamlit team to investigate. A specific Streamlit version like 1.50.0 is particularly helpful, as it allows for targeted debugging of changes introduced around that release.

The fact that this issue is reproducible on a specific version and OS combination indicates a definite bug rather than an intermittent problem.

Conclusion and Looking Forward

The st.plotly_chart deprecation warning when using width="content" is a clear indicator of a small but noticeable bug or regression in Streamlit. While the underlying plotting functionality likely remains unaffected, the warning itself creates confusion and detracts from a clean developer experience. The expected behavior is that documented parameters for controlling chart dimensions should not trigger warnings about the misuse of variable keyword arguments.

This issue highlights the ongoing effort to refine Streamlit's API and ensure clear communication between the library and its users. As Streamlit evolves, such nuances in argument handling are important to address promptly.

For those encountering this, the workaround is to simply ignore the warning if the chart displays correctly, or to use fixed pixel values for width and height if the warning is too disruptive. However, the ideal solution is for the Streamlit team to adjust the internal logic to correctly differentiate between its own display parameters and arbitrary kwargs.

If you're interested in the broader context of Streamlit development and how such issues are managed, you can explore the official Streamlit GitHub repository. It's a great resource for understanding the library's development, contributing to discussions, and staying updated on bug fixes and new features.

Happy visualizing!