Streamlit Plotly_chart Width Argument Deprecation Warning

Hey there, data enthusiasts and Streamlit lovers! Have you ever been building a slick dashboard with Streamlit and encountered a rather annoying deprecation warning when using st.plotly_chart with the width="content" or height argument? You're not alone! It seems that even when you're diligently following the documentation and only using documented parameters, a warning about kwargs can pop up. This can be super confusing, making you wonder if you're doing something wrong. Let's dive deep into this and figure out what's going on.

The Mystery of the kwargs Warning in st.plotly_chart

So, you're creating a beautiful Plotly chart in your Streamlit app. You want it to perfectly fit the container, so you set width="content". Easy peasy, right? Well, according to the warning message that might greet you, not quite. The issue arises because of how Streamlit handles arguments passed to st.plotly_chart. When you pass arguments like width or height that aren't explicitly part of the core plotly_chart function's direct parameters, Streamlit's internal logic might interpret them as variable keyword arguments (kwargs). This leads to a deprecation warning being triggered, even if you're not intentionally using **kwargs in your own code.

This is a real head-scratcher, especially when the documentation clearly shows width and height as valid parameters for controlling the chart's dimensions. The warning essentially says, "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 suggests that perhaps the way width and height are being handled internally is being flagged as a deprecated practice. It's a bit like calling a trusted friend by an old nickname – they know who you mean, but it's not the name they prefer anymore. The core functionality might still work, but the underlying mechanism is a bit out of date. It's important to remember that deprecation warnings are there to guide developers towards more future-proof practices. While it might not break your app today, it's a signal that the way things are done might change. In this specific case, it seems the warning is a bit too eager, flagging even standard, documented usage. This can lead to unnecessary noise in your development console, making it harder to spot actual critical issues.

The code snippet that seems to be causing this fuss is within Streamlit's internal handling of st.plotly_chart. It looks something like this: if kwargs: show_deprecation_warning(...). This conditional statement checks if there are any kwargs passed to the function. If the width="content" or height arguments are being processed in a way that triggers this kwargs check, the warning will fire. The intention behind this warning is to steer users towards the config argument for Plotly-specific configurations, which is a good practice for managing complex Plotly settings. However, in this instance, it appears to be catching broader arguments related to the chart's display within Streamlit itself, leading to a false positive.

Why This Matters to You

This isn't just a minor annoyance; it's a usability issue. When you see a deprecation warning, especially one that seems to contradict the documentation, it can:

1. Cause confusion: You might spend time trying to figure out what kwargs you're supposedly passing.
2. Mask real issues: Genuine deprecation warnings or errors could get lost in the noise.
3. Create uncertainty: You might worry about future compatibility or whether your current code is robust.

It's a bit like getting a notification that your car is overheating when you're just driving slowly in cool weather – it's alarming, but ultimately harmless and just plain wrong. The goal is to have clear, actionable feedback, and this warning, in this context, isn't quite hitting the mark. It's a testament to the rapid development of libraries like Streamlit and Plotly, where features are constantly being refined. Sometimes, these refinements can lead to these little hiccups where warnings fire a bit too broadly. The Streamlit team is usually quick to address such issues, as they understand the importance of a clean and predictable developer experience. The core functionality of st.plotly_chart remains strong, but these warnings can be a distraction.

Reproducing the Warning: A Simple Code Example

To help understand and potentially fix this, the Streamlit community has provided a clear, reproducible example. It's quite straightforward and highlights the problem effectively:

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 simple script in Streamlit, you'll likely see the deprecation warning mentioned earlier, even though you're only using the documented width="content" parameter for st.plotly_chart. There are no explicit **kwargs being passed from your end. This code is clean, concise, and directly demonstrates the issue. It isolates the problem to the interaction between st.plotly_chart and how it handles the width argument, especially when that argument is set to a dynamic value like "content". The fact that it's reproducible with such minimal code makes it easier for the Streamlit developers to pinpoint the exact line of code or logic that needs adjustment. It's the kind of bug report that gets developers excited because it's clear-cut and actionable.

The Expected vs. Actual Behavior

• Expected Behavior: You'd anticipate that using st.plotly_chart(fig, width="content") would simply render the Plotly chart with its width adjusted to fit the content, without any deprecation warnings related to kwargs. The documentation for st.plotly_chart indicates that width is a valid parameter for controlling the plot's dimensions. When use_container_width was deprecated, width was presented as its replacement, and it's expected to work seamlessly. So, ideally, this call should be silent and effective.

• Current Behavior: As observed, the code triggers a deprecation warning: Variable keyword arguments for st.plotly_chart have been deprecated.... This warning appears even though the width parameter is a documented feature and not being passed as a generic **kwargs. This indicates a potential mismatch between Streamlit's internal argument parsing and its warning system.

This discrepancy is particularly noticeable because Streamlit versions prior to this behavior did not exhibit this warning. The prompt mentions this is a regression, meaning it worked correctly in a previous version, and this behavior was introduced in a later update. This suggests that a change in Streamlit's codebase, likely related to argument handling or the deprecation warning logic, inadvertently caused this issue. The team's commitment to iterating and improving means that sometimes, these types of bugs slip through. However, the community's vigilance in reporting them is key to ensuring a smooth experience for everyone.

Diving Deeper: The config Argument and Future-Proofing

Streamlit's warning suggests using the config argument for Plotly configuration options. This is a valid and important point. The config argument in st.plotly_chart is designed to accept a dictionary of Plotly.js configuration options. These are settings that control the behavior and appearance of the Plotly chart's interactive elements, such as tooltips, mode bar buttons, and responsiveness.

For example, if you wanted to customize the mode bar that appears when hovering over a Plotly chart, you would use the config argument:

config_options = {
    "scrollZoom": True,
    "displaylogo": False
}
st.plotly_chart(fig, config=config_options)

This approach is indeed the recommended way to pass Plotly-specific settings. However, the warning we're discussing seems to be conflating these Plotly-specific configurations with arguments that control the Streamlit component's behavior, like width and height. The width and height arguments in st.plotly_chart primarily control how the chart is displayed within the Streamlit layout, rather than how the Plotly chart itself functions internally. Therefore, using width="content" should ideally not trigger a warning about Plotly configuration options being passed via kwargs.

The core of the issue seems to be in Streamlit's internal processing of the st.plotly_chart function. When you pass arguments like width or height, Streamlit's underlying mechanism might be treating them as if they were part of a general keyword argument pool that is intended for Plotly's internal config settings. This is likely an unintended consequence of refactoring or updates to how Streamlit handles arguments passed to its components. The warning is intended to guide users away from passing Plotly configurations directly as keyword arguments to st.plotly_chart (e.g., st.plotly_chart(fig, showLink=True)), and instead direct them to the config dictionary. However, the current implementation seems to be too broad and is catching arguments like width that are meant to control the component's rendering within Streamlit itself.

It's crucial for developers to understand the distinction between Streamlit's layout control parameters and Plotly's internal configuration options. By addressing this warning, Streamlit can provide a cleaner and more intuitive experience, ensuring that developers can focus on building their applications without being sidetracked by potentially misleading warnings. The goal is to have a clear separation of concerns: Streamlit manages the layout and component rendering, while Plotly manages the chart's internal features and data visualization logic.

Is This a Regression? Yes!

As stated in the issue report, this is indeed a regression. This means that in a previous version of Streamlit, using st.plotly_chart(fig, width="content") worked perfectly fine without any accompanying deprecation warnings. This is a critical piece of information because it indicates that a recent change in Streamlit's codebase has introduced this behavior, rather than it being an intended long-standing feature. Regressions can be frustrating, but they also provide a clear target for developers to fix. The fact that it worked before means the fundamental capability is there; it's just a matter of restoring the correct behavior. Identifying it as a regression helps prioritize the fix, as it impacts existing, functional code. It suggests that during an update or refactor, the logic for handling width and height arguments, or the conditions under which the kwargs warning is triggered, was altered in a way that caused this unintended side effect. The Streamlit team values stability and backward compatibility, so addressing regressions is typically a high priority.

Debugging Information Provided

The issue report also includes valuable debugging information, which is essential for developers to diagnose and resolve the problem:

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

This information helps establish the environment in which the bug occurs. Having specific version numbers allows developers to test against the exact conditions reported and ensures that the fix is validated in the same setup. For instance, knowing the Streamlit version is crucial because the behavior might be specific to that release or a range of releases.

Conclusion and Next Steps

This kwargs deprecation warning when using st.plotly_chart with width="content" (or height) is a frustrating but likely fixable bug. It appears to be a case where Streamlit's argument handling or warning system is being overly sensitive, flagging documented and intended usage as a deprecated practice. The good news is that it's reproducible with simple code and has been identified as a regression, giving the Streamlit team a clear path to resolution.

For users experiencing this, while a fix is hopefully on its way, you might consider a temporary workaround if the warning is significantly disruptive. However, the best course of action is to keep an eye on the Streamlit GitHub repository for updates. The Streamlit community is incredibly active, and issues like this are usually addressed promptly. Understanding the difference between Streamlit's layout parameters and Plotly's configuration options, and using the config argument for the latter, remains a best practice for building robust and maintainable Streamlit applications.

We're confident that the Streamlit team will squash this bug, ensuring a smoother experience for everyone creating interactive dashboards. Happy coding!

For more in-depth information on Streamlit components and best practices, you can always refer to the official Streamlit Documentation. And for deep dives into Plotly configurations, the Plotly Python Graphing Library Documentation is an invaluable resource.