Streamlit Plotly Chart Width Warning Fix

Have you ever been in the middle of building a fantastic interactive dashboard with Streamlit, only to be greeted by a cryptic deprecation warning from st.plotly_chart? You meticulously followed the documentation, used seemingly standard parameters like width="content", and yet, there it is – a warning about kwargs that makes you scratch your head. You might be thinking, "But I didn't pass any **kwargs! What's going on?" Well, you're not alone in this. This particular hiccup has been a point of confusion for many, and understanding why it happens is key to a smoother Streamlit experience. This article dives deep into this specific deprecation warning, explaining its origins, why it appears even when you're not explicitly using variable keyword arguments, and how to effectively navigate it to ensure your Streamlit apps run without unnecessary warnings.

The Curious Case of the kwargs Warning in st.plotly_chart

Let's start by unraveling the mystery behind the kwargs deprecation warning when using st.plotly_chart with the width="content" parameter. The core of the issue lies in how Streamlit handles arguments passed to its components, particularly when those arguments are intended for the underlying library – in this case, Plotly. When you use st.plotly_chart(fig, width="content"), Streamlit is designed to pass this width parameter, along with others, to the Plotly figure for rendering. 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 triggered because Streamlit's internal logic interprets certain parameters, even documented ones like width, as potentially falling into the category of kwargs that are being refactored.

Think of it like this: Streamlit has a main set of controls for its own functions, like width and height for the chart container itself. However, Plotly charts have their own extensive set of configuration options that you can pass through. Historically, there might have been a more lenient way to pass these Plotly-specific configurations directly as keyword arguments to st.plotly_chart. As Streamlit evolves, they are tightening up their API to be more explicit and less prone to unexpected behavior. The config parameter was introduced as the dedicated channel for passing Plotly-specific configurations, ensuring that Streamlit's own parameters and Plotly's internal parameters don't get mixed up.

The width="content" parameter, while a valid and useful way to make your Plotly charts responsive to their container, seems to be caught in this transition. Even though you're not intentionally passing arbitrary kwargs, Streamlit's warning system flags it because the underlying mechanism for handling these parameters is being updated. It's a protective measure, ensuring developers are nudged towards the newer, more robust config parameter for Plotly-specific settings. The good news is that this warning doesn't necessarily indicate a functional bug in your code; rather, it's a signal about an evolving API and a recommended best practice for future compatibility. We'll explore the exact code that triggers this and how to implement the recommended solution in the following sections.

Diving into the Code: Where Does the Warning Originate?

To truly understand the kwargs deprecation warning in st.plotly_chart, it's helpful to look at the code that's causing it. As reported, the warning is triggered by a specific conditional block within Streamlit's plotly_chart function. The relevant snippet 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."
 )

This if kwargs: condition checks if there are any keyword arguments passed to the st.plotly_chart function that are not explicitly handled by Streamlit itself. When you call st.plotly_chart(fig, width="content"), Streamlit processes its own known arguments (like use_container_width, height, width, sharing, etc.) and then passes any remaining keyword arguments to Plotly for rendering. The width="content" parameter, even though it's a documented parameter for controlling the chart's width, is being interpreted by this check as a variable keyword argument that falls outside of Streamlit's primary control.

The underlying issue is a semantic one. Streamlit has its own set of arguments that control how the chart is displayed within the Streamlit app (e.g., the container width, aspect ratio). Plotly, on the other hand, has its own extensive configuration options that control the chart's internal behavior and appearance (e.g., axis labels, hover information, trace properties). The config parameter was introduced as the standardized way to pass these Plotly-specific settings. When you pass width="content", Streamlit might be passing this down to Plotly's configuration, and the if kwargs: check, designed to catch any extra keyword arguments that should ideally go through config, is firing.

This is why the warning appears even when you're not passing arbitrary, undocumented parameters. It's a broad catch-all designed to encourage the use of the config dictionary for all Plotly-specific customizations. The intention is to make the API clearer: Streamlit arguments control the Streamlit container, and the config argument controls the Plotly chart itself. While width="content" is a valid Streamlit-level control for responsiveness, its internal handling might be crossing paths with the new kwargs deprecation logic.

The Expected vs. Current Behavior: A Closer Look

Let's clearly define what we expect and what is currently happening. When Streamlit introduced changes to how keyword arguments are handled in st.plotly_chart, the goal was to streamline the API and guide users towards more explicit configurations. Specifically, parameters that were previously accepted directly as keyword arguments and were meant for Plotly's internal configuration were to be moved to the config argument. The width and height parameters within st.plotly_chart have a dual role: they can control the dimensions of the container that holds the Plotly chart, and in some contexts, they might influence how Plotly itself renders.

Expected Behavior:

Following the documentation, when you use st.plotly_chart(fig, width="content"), it's expected that this would translate to the chart container adjusting its width to fit the content. This is a documented and intended use case for controlling chart responsiveness. Therefore, the expectation is that this usage should not trigger a deprecation warning. If the width argument is indeed meant to be a valid Streamlit-level control for responsiveness, it should be handled gracefully without implicating the kwargs deprecation.

Current Behavior:

As observed, the current behavior deviates from this expectation. When you use st.plotly_chart(fig, width="content"), the application still displays the 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." This occurs because, as discussed, the internal mechanism that checks for unhandled keyword arguments is being triggered by the width parameter. Even though width is a documented parameter for controlling the chart's display size within Streamlit, the deprecation warning suggests that such direct parameter passing might be phased out in favor of the config dictionary.

This discrepancy highlights a potential oversight or a transitional phase in Streamlit's API. While the intention of the deprecation is clear – to funnel Plotly customizations through the config argument – it appears that some of Streamlit's own responsive design parameters, like width="content", are inadvertently triggering this warning. This is particularly problematic because it can lead users to believe they are using the API incorrectly when, in fact, they are using a documented feature that is now being flagged. The