Fix Plotly Chart Width Warning In Streamlit

Understanding the kwargs Deprecation Warning in Streamlit

Have you ever encountered a mysterious deprecation warning when using Streamlit's st.plotly_chart function, even when you're sure you haven't passed any extraneous keyword arguments? It can be quite puzzling, especially when you're just trying to set the width or height of your Plotly charts. This is precisely the issue we're diving into today. Specifically, we're looking at a scenario where using width="content" (or its counterpart, height="content") triggers a kwargs deprecation warning, even though you're only utilizing documented parameters. This can lead to confusion and a less-than-ideal developer experience. The warning message itself hints at a broader change: "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." While this is a valid and important update for Streamlit's internal handling of arguments, its current implementation seems to be inadvertently flagging legitimate uses of the width and height parameters. This means that even when you're following the documentation and using parameters like width="content", Streamlit might still show this warning, making it seem like you're doing something wrong when, in fact, you're not. This isn't just a minor annoyance; it can distract developers from their actual task and cast doubt on the correctness of their code. The goal of a good API is to be clear and intuitive, and when documented features trigger warnings intended for undocumented or misused features, that clarity is compromised. We'll explore why this happens and how to navigate it effectively.

The Code Behind the Confusion: A Reproducible Example

To truly grasp the issue, let's look at a concrete example. Imagine you're building a Streamlit application and want to display an interactive Plotly chart. You've created a simple go.Figure object, perhaps a barpolar chart, and you want it to dynamically adjust its width based on its content. This is where st.plotly_chart(fig, width="content") comes into play. Here's the code snippet that triggers this warning:

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")

When you run this code, Streamlit version 1.50.0 (or similar versions affected by this change) with Python 3.14.2 on macOS 26.1 (or other operating systems) using Chrome (or other browsers) will present you with 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.

It's important to note that in this example, we are not explicitly passing any variable keyword arguments (kwargs) that aren't part of the documented API for st.plotly_chart. The width="content" argument is a documented way to control the chart's display. The warning arises because Streamlit's internal logic, introduced around the time of specific pull requests addressing kwargs handling, incorrectly identifies the width parameter (when set to "content") as an instance of variable keyword arguments that should be managed through the config dictionary. This creates a false positive, where a correct usage of the API leads to a warning that suggests a misuse or an upcoming breaking change for parameters that are still very much in use and supported according to the documentation. This discrepancy between expected behavior and actual output is what makes this a regression – it worked fine in previous versions and now it doesn't, causing unnecessary friction for developers trying to leverage Streamlit's features.

The Root Cause: Internal Argument Handling

The core of this issue lies in how Streamlit processes arguments passed to st.plotly_chart. As mentioned in the issue report, a change was introduced to manage variable keyword arguments (kwargs) more strictly. The intent behind this change was to guide users towards using the config parameter for Plotly-specific settings, thereby streamlining the argument handling and future-proofing the component. The code snippet responsible for this 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 problem arises because the width parameter, when set to a string value like "content", is being caught by this if kwargs: condition. This condition is intended to catch any remaining keyword arguments that are not explicitly handled by st.plotly_chart itself. However, it seems that width="content" is being interpreted as a generic kwargs entry rather than a recognized, albeit special, parameter for controlling the chart's dimensions. This suggests that the logic for differentiating between explicit, documented parameters and true, unhandled variable keyword arguments might need refinement. It's a classic case of an internal refactor, aimed at improving code quality and robustness, having an unintended side effect on user-facing functionality. The developers likely didn't intend for documented parameters like width to trigger this warning, but the way the argument parsing is set up, it treats it as an unmanaged keyword argument.

Why It's a Regression and What's Expected

This behavior is indeed a regression because, in previous versions of Streamlit, using st.plotly_chart with width="content" (or height="content") did not produce any deprecation warnings. Users could seamlessly control the responsive behavior of their Plotly charts without any console noise. The expectation is that Streamlit's st.plotly_chart function should gracefully handle its documented parameters. When a user provides width="content", they are utilizing a feature designed to make their charts adapt to the container's width. The expected behavior is that this parameter is accepted and processed correctly, and no warning related to deprecated kwargs should appear. The warning we are seeing implies that width="content" is being treated as an unknown or deprecated keyword argument, which contradicts its status as a documented and functional parameter. The config argument in Streamlit is primarily for passing Plotly's own layout.config options, not for controlling the overall dimensions of the chart within the Streamlit app itself. Therefore, redirecting users to config for this specific use case is not accurate and adds to the confusion. The ideal scenario is that Streamlit correctly distinguishes between its own component-level arguments (like width and height) and Plotly's internal configuration options, ensuring that documented features work as expected without generating misleading warnings. This regression impacts the user experience by introducing unnecessary alerts and potentially confusing developers about how to correctly size their charts in a responsive manner.

Navigating the Current Behavior and Potential Workarounds

Given the current behavior, you might be wondering what you can do. While the ideal solution is for Streamlit to address this regression, there are a couple of ways to navigate this situation. The most straightforward approach, if you can tolerate the warning, is to simply ignore it. Since you know that width="content" is a documented parameter and the warning is a false positive, you can proceed with your development. However, this isn't ideal for a clean console output. A more proactive workaround involves using the config argument, not for its intended purpose of Plotly's internal configuration, but to suppress the warning. This is a bit of a hack, but it can be effective. You could try passing an empty dictionary to the config argument, like so:

st.plotly_chart(fig, width="content", config={})

This might satisfy Streamlit's internal check for kwargs in a way that avoids the warning. However, it's crucial to understand that this is a workaround, not a fix. The config parameter is meant for Plotly's layout.config options (e.g., 'scrollZoom': True). Using it solely to suppress a warning might be confusing and could potentially interfere with actual Plotly configurations if you later decide to use config as intended. Another approach could be to avoid using width="content" altogether and instead specify a fixed pixel width for your chart, such as width=700. This bypasses the problematic parameter entirely but sacrifices the responsiveness that width="content" provides. The best long-term solution, of course, is for the Streamlit team to refine the argument parsing logic to correctly identify and handle documented parameters like width="content" without triggering the kwargs deprecation warning. Until then, carefully consider the trade-offs of each workaround.

The Path Forward: Addressing the Regression

This issue highlights the delicate balance between refactoring code for internal improvement and maintaining a seamless user experience. While the move to manage kwargs more explicitly in st.plotly_chart is a positive step towards cleaner code and better maintenance, its current implementation has created an unintended regression. The fix requires Streamlit developers to revisit the argument parsing logic for st.plotly_chart. Specifically, they need to ensure that documented parameters like width and height, especially when used with special string values like "content", are correctly recognized and handled. The if kwargs: check should ideally only flag truly unhandled or unexpected keyword arguments, not parameters that are explicitly part of the component's public API. This might involve creating a more robust whitelist or mechanism for identifying known parameters before invoking the deprecation warning. By refining this logic, Streamlit can ensure that developers can continue to use features like responsive chart sizing without encountering misleading warnings. This will restore the expected behavior, where documented parameters function as intended without generating unnecessary alerts, thereby improving the overall stability and user-friendliness of the Streamlit library. For users encountering this, reporting the issue and providing clear, reproducible examples, as was done here, is the most effective way to help the development team identify and address such regressions promptly. It's a collaborative effort to keep Streamlit robust and reliable.

For more information on Plotly and its configurations, you can refer to the official Plotly Documentation. For Streamlit-specific issues and discussions, the Streamlit GitHub Repository is an excellent resource.