Fixing Streamlit's Plotly_chart Width Warning

Dec 20, 2025 by Alex Johnson 46 views

Streamlit's plotly_chart: Untangling the Width Argument and Deprecation Warnings

Hey there, data visualization enthusiasts! Have you ever been tinkering with Streamlit, crafting some beautiful Plotly charts, only to be met with a pesky deprecation warning? You're not alone! It seems that when you try to set the width of your st.plotly_chart to something like "content", you might get a warning about kwargs even if you're not doing anything out of the ordinary. Let's dive into what's happening and how we can navigate this.

The Unexpected Warning: When `width="content"` Causes a Stir

So, you're building a Streamlit app, and you want your Plotly charts to be nicely responsive, filling the available container width. A common way to achieve this is by setting the width parameter in st.plotly_chart to "content". It seems straightforward, right? You'd expect your chart to just work, adapting its size to the container. However, some users have reported encountering a deprecation warning related to variable keyword arguments (kwargs) even when they haven't explicitly passed any extra, undefined keyword arguments. This can be a bit confusing because you're only using documented parameters, like width and height, which are clearly part of the st.plotly_chart API.

This particular warning, often mentioning that "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," can pop up unexpectedly. It implies that there's some form of kwargs being passed that Streamlit's internal logic doesn't expect, or perhaps it's a byproduct of how Streamlit handles certain arguments. The core of the issue lies in the fact that using width="content" (or height="content") seems to trigger this warning, suggesting an internal mechanism that's interpreting these arguments in a way that leads to the deprecation notice, even though they are valid and intended uses.

This isn't just a minor annoyance; it can mask actual deprecation warnings or make your console output look messy, potentially hiding important information. For developers aiming for clean, professional-looking applications, these unexpected warnings can be a real head-scratcher. It's a situation where the expected behavior (a responsive chart without warnings) doesn't quite match the current behavior (a responsive chart with a kwargs deprecation warning).

The good news is that this seems to be a known issue, and developers are aware of it. Understanding why it happens is the first step to finding a workaround or eagerly awaiting a fix. The warning itself points towards using the config argument for Plotly-specific configurations. However, width and height in st.plotly_chart are Streamlit-specific arguments for controlling the display of the chart within the Streamlit app, not necessarily for deep Plotly configuration. This distinction is crucial – config is for Plotly's internal settings, while width and height are for Streamlit's layout.

It appears that the underlying implementation of st.plotly_chart might be processing the width and height arguments in a way that inadvertently flags them as generic keyword arguments, thus triggering the broader kwargs deprecation warning. This could be due to how these arguments are passed down to the Plotly rendering engine or how Streamlit's component system handles them. The goal is simple: to use width="content" and have the chart fit nicely without any warnings.

Reproducing the Issue: A Simple Code Snippet

To make sure we're all on the same page, let's look at a straightforward way to reproduce this behavior. The Streamlit team often emphasizes the importance of reproducible examples, and for this particular issue, it's quite simple:

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]))
fig.update_layout(width=500, height=360) # These are Plotly's layout settings

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

When you run this code in a Streamlit application (especially with versions like 1.50.0, as reported by users), you'll likely see your Barpolar chart rendered correctly. It should adapt its width to the container it's placed in. However, if you check your Streamlit console or the terminal where you're running the app, you'll probably find that deprecation warning mentioned earlier. It's quite peculiar because the width="content" argument is a documented feature of st.plotly_chart intended for responsive sizing. You're not passing any arbitrary **kwargs yourself; you're using a specific, documented parameter.

This highlights a potential disconnect between how Streamlit processes its own component arguments (width, height) and its internal warning system for Plotly's kwargs. The warning is designed to catch users passing non-standard Plotly arguments directly, but in this case, it seems to be misfiring for a Streamlit-specific directive. The expected behavior here is clear: the chart should render responsively, and importantly, without any deprecation warnings. The fact that it's a regression suggests that in a previous version, this setup worked without any such alerts.

It's this very reproducibility that helps developers pinpoint the exact cause. By isolating the issue to a specific parameter (width="content") and a specific function (st.plotly_chart), the Streamlit team can more effectively investigate the internal code paths that lead to this warning. The provided code example is concise and effectively demonstrates the problem, allowing for quick verification and debugging.

The Expected vs. Current Behavior: What Should Happen and What Is Happening

Let's break down the core of the problem by comparing what we expect to happen with st.plotly_chart versus what's actually occurring.

Expected Behavior:

When you use st.plotly_chart(fig, width="content"), the expectation is that the Plotly chart will intelligently adjust its width to fill the available space within its Streamlit container. This is a fundamental aspect of creating responsive web applications, ensuring that your visualizations look good on various screen sizes and within different app layouts. Furthermore, and crucially, this action should not trigger any deprecation warnings. The width parameter, especially when set to "content", is a documented and intended way to control the chart's display size within the Streamlit framework. You're not trying to pass arbitrary Plotly configurations here; you're using Streamlit's interface to manage the visual presentation.

Current Behavior:

As reported, the current behavior deviates from this expectation. When you use st.plotly_chart(fig, width="content"), the chart is indeed displayed, and it often resizes as intended. However, alongside the visible chart, a deprecation warning appears in the console. This warning typically reads something like: "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 triggered even though the user is not explicitly passing any non-standard keyword arguments. The width="content" is a standard, documented parameter for st.plotly_chart.

The underlying cause seems to be related to changes made in Streamlit's handling of kwargs. A recent update (or a series of updates) might have introduced stricter checks or a different internal routing for arguments passed to st.plotly_chart. It appears that when width or height are set to special values like "content", the way these arguments are processed internally might inadvertently trigger the kwargs warning mechanism. This mechanism is generally meant to warn users about passing unsupported or deprecated Plotly arguments directly, but in this specific scenario, it seems to be a false positive, flagging a valid Streamlit directive as an unexpected kwargs use.

This mismatch is particularly noticeable because the warning message itself suggests using the config argument for Plotly settings. However, width and height are Streamlit's own parameters for layout control, distinct from Plotly's internal configuration options. The desired outcome is a chart that fits the container and a console that remains free of misleading warnings. The fact that this is considered a regression indicates that this specific usage worked seamlessly in earlier versions of Streamlit, making the current behavior a step backward for developers relying on this functionality.

Is This a Regression? Understanding the Impact

Yes, based on the user reports and the nature of the problem, this situation is indeed a regression. This means that the functionality, which used to work as expected in a previous version of Streamlit, is now behaving incorrectly or causing unintended side effects. For developers who have built applications relying on the st.plotly_chart function's ability to handle responsive sizing via width="content" without raising spurious warnings, this change can be disruptive.

Why it Matters as a Regression:

Breaking Expectations: Users expect a stable API. If a documented feature that previously worked without issues suddenly starts producing warnings, it breaks that expectation of stability. This can lead to confusion and a loss of confidence in the library's robustness.
Code Clutter and Masking: Deprecation warnings, even if not critical errors, add noise to the console output. In a complex application, these warnings can obscure other, more important error messages or warnings, making debugging harder. If developers get used to ignoring this specific warning, they might miss genuine issues.
Impact on Workflow: For developers who value clean logs and a well-behaved application, encountering such warnings can disrupt their workflow. They might spend time investigating a non-issue or implementing workarounds that aren't strictly necessary.
Undermining Documentation: When documentation suggests a feature works in a certain way (e.g., using width="content" for responsiveness), and the implementation then warns against it, it can create a contradiction. Users rely on documentation to guide their implementation, and inconsistencies can be frustrating.

The fact that this is a regression underscores the importance of thorough testing, especially around API changes and argument handling. When Streamlit updated its handling of keyword arguments or Plotly integration, this specific edge case seems to have been overlooked or introduced unintentionally. Recognizing it as a regression allows the development team to prioritize its fix, as regressions often take precedence over new feature development due to their disruptive nature.

It’s a reminder that even seemingly minor changes in how arguments are processed can have ripple effects. The goal is to ensure that documented features work as advertised and that the user experience remains smooth and predictable. A regression like this, while often resolvable, is a clear indicator that something in the recent development cycle has gone awry.

Debugging the `kwargs` Warning: A Closer Look

To truly understand the kwargs deprecation warning issue with st.plotly_chart when using width="content", we need to peek under the hood a bit. The warning itself, often phrased as: "Variable keyword arguments for st.plotly_chart have been deprecated... Use the config argument instead," is a signal that Streamlit's internal argument parsing has identified something it considers an unexpected or deprecated keyword argument. Let's dissect this:

The Role of kwargs: In Python, **kwargs is a special syntax that allows a function to accept an arbitrary number of keyword arguments. These arguments are then collected into a dictionary. The warning suggests that passing arguments this way to st.plotly_chart (beyond the explicitly defined ones) is being discouraged in favor of using the config parameter for Plotly-specific settings.
The Misdirection: The core of the problem is that width="content" is not a Plotly configuration option that should be passed via config. Instead, it's a Streamlit-specific directive for controlling the layout and rendering size of the Plotly chart within the Streamlit app itself. Streamlit's st.plotly_chart function has its own set of parameters like height, width, use_container_width (which width="content" essentially replaces or augments), and config.
Internal Processing: It appears that Streamlit's internal machinery, when encountering width="content", might be passing this argument down in a way that triggers the kwargs detection. This could happen if st.plotly_chart internally uses **kwargs to pass arguments to a lower-level rendering component or directly to Plotly's JavaScript, and width="content" gets caught in that net. The warning is likely intended for users who might try to pass things like title='My Title' or xaxis={'title': 'X-axis'} directly to st.plotly_chart instead of using fig.update_layout() or the config parameter. However, it's misfiring for the width parameter.
Version Specificity: The fact that this is often reported with specific Streamlit versions (like 1.50.0) suggests that the way arguments are handled has changed. Perhaps a refactoring of the st.plotly_chart function or the underlying component system led to this unintended consequence. The goal of such refactoring is often to improve performance, add new features, or simplify the API, but sometimes, it can introduce regressions like this.
The config Argument: The warning correctly points to using the config argument for Plotly-specific settings that you might have previously passed as kwargs. For instance, if you were setting Plotly's responsive: true or displayModeBar: 'false', these should now go into config={'responsive': True, 'displayModeBar': False}. But width and height remain Streamlit's domain for controlling the component's size on the page.

In essence, Streamlit is warning about kwargs when it should be recognizing width="content" as a valid, Streamlit-level parameter. The debug information provided, such as the Streamlit version, Python version, OS, and browser, is crucial for pinpointing this behavior, as it might be specific to certain environments or versions.

Moving Forward: Solutions and Best Practices

While we await a definitive fix from the Streamlit team, there are a couple of ways to navigate this kwargs deprecation warning when using st.plotly_chart with responsive sizing:

Use use_container_width=True: This is the most direct and recommended alternative that often bypasses the warning. Streamlit's st.plotly_chart function has a parameter specifically designed for responsive behavior: use_container_width. Setting this to True achieves the same goal as width="content" – making your chart fill the available width – and it typically does not trigger the kwargs 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) # Layout width/height is for Plotly's canvas, not Streamlit's component size

st.plotly_chart(fig, use_container_width=True)
```
This approach aligns perfectly with Streamlit's intent for controlling component sizing and avoids the internal argument handling that seems to trigger the warning.
Explicitly Set Width/Height (If Possible): If use_container_width=True doesn't fit your specific layout needs, and you must specify a pixel width or height, you can do so. However, be mindful that setting a fixed width or height in st.plotly_chart (e.g., st.plotly_chart(fig, width=800, height=400)) might still sometimes interact unexpectedly with the kwargs system, though it's generally less problematic than "content". The primary issue seems to be with the string value "content" being interpreted in a particular way.
Ignore the Warning (with caution): If the warning is truly a false positive and doesn't affect your application's functionality, you could choose to ignore it. However, this is generally not recommended, as it can lead to clutter in your logs and might mask genuine issues. It's better to find a solution that eliminates the warning.
Update Streamlit: Keep your Streamlit installation updated. While this specific issue might be present in certain versions, future releases will likely address and resolve such regressions. Checking the release notes for st.plotly_chart updates can also provide insights.

Best Practices Recap:

Prioritize use_container_width=True: For responsive charts, this is your go-to parameter.
Use config for Plotly Settings: If you need to control Plotly's behavior (like interactivity, display modes, etc.), use the config dictionary.
Use fig.update_layout() for Figure Aesthetics: For titles, axes labels, colors, and other visual aspects of the plot itself, fig.update_layout() remains the standard method.
Stay Updated: Regularly update Streamlit to benefit from bug fixes and improvements.

By adopting these practices, you can ensure your Streamlit applications are both functional and free from unnecessary warnings, leading to a smoother development and user experience.

Conclusion: Towards a Smoother Visualization Experience

Navigating the nuances of libraries like Streamlit and Plotly can sometimes feel like a balancing act. The st.plotly_chart function is a powerful tool for bringing interactive visualizations into your web applications, but as we've seen, it can occasionally present unexpected challenges, such as the deprecation warning related to kwargs when using width="content". This particular issue highlights how internal argument handling and warning systems can sometimes create false positives, leading to developer confusion.

The good news is that recognizing this as a regression and understanding the difference between Streamlit's layout parameters (width, height, use_container_width) and Plotly's internal configuration (handled via config or fig.update_layout()) provides a clear path forward. The most effective workaround is to leverage use_container_width=True, which is specifically designed for the responsive behavior users often seek.

As the Streamlit community continues to grow and evolve, issues like these are invaluable feedback loops. They help developers refine the library, ensuring that it remains user-friendly, robust, and predictable. By staying informed, utilizing best practices, and communicating issues effectively (like the one discussed here), we collectively contribute to a better data science and app development ecosystem.

For further exploration into Streamlit's charting capabilities and best practices for integration with Plotly, I highly recommend checking out the official Streamlit documentation on displaying charts. Additionally, the Plotly documentation offers a deep dive into the vast customization options available for your plots.