Streamlit Plotly Chart: Fix Width Deprecation Warning

When you're building interactive dashboards and data visualizations with Streamlit, you often want to have fine-grained control over the appearance of your plots. One common requirement is to adjust the width and height of your Streamlit elements, including charts. This is where the st.plotly_chart function comes into play. It allows you to seamlessly integrate Plotly figures into your Streamlit applications. However, users have recently encountered a rather persistent deprecation warning when trying to set the width or height using the "content" value, even when they aren't explicitly passing any variable keyword arguments. This can be a bit confusing, as you're just trying to use the documented parameters as intended. Let's dive into why this happens and how you can navigate this situation effectively.

Understanding the st.plotly_chart Function and Keyword Arguments

The st.plotly_chart function is designed to display Plotly figures within your Streamlit app. It accepts a Plotly figure object as its primary argument. Additionally, it offers several optional parameters to customize the chart's display, such as use_container_width, width, and height. Historically, Streamlit's components, including st.plotly_chart, have evolved, and sometimes parameters are updated or deprecated to make way for more streamlined or robust solutions. The recent change that's causing this warning involves how keyword arguments (kwargs) are handled internally.

Streamlit introduced a deprecation warning related to variable keyword arguments for st.plotly_chart. The intention behind this change was to encourage users to utilize the config argument for passing Plotly-specific configurations, rather than relying on general keyword arguments that might not be directly supported or could lead to future compatibility issues. This is a good practice for maintaining code clarity and ensuring that your applications remain stable as Streamlit and Plotly evolve. However, in the current implementation, this warning is being triggered even when users specify documented parameters like width="content" or height="content". This suggests a slight misfire in the warning's detection logic – it's flagging a valid, documented use case as if it were an unsupported variable keyword argument.

The core of the issue lies in the way Streamlit checks for kwargs. 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 intended for situations where you might be passing arbitrary keyword arguments that Plotly or Streamlit don't explicitly recognize or handle. However, the current code seems to be broadly applying this check, catching even the explicitly documented width and height parameters when set to "content". This creates a situation where users are seeing a warning for behavior that is, according to the documentation, perfectly acceptable and expected.

It's important to remember that deprecation warnings are there to help you prepare for future changes. They signal that a certain way of doing things might be phased out. While it's frustrating to see a warning for a valid use case, understanding the underlying mechanism can help you address it and also contribute to improving the Streamlit library itself. The developers are aware of this behavior, and it's likely that future versions of Streamlit will refine this warning mechanism to distinguish between true variable keyword arguments and documented parameters like width and height.

Reproducing the Warning: A Simple Code Example

To illustrate the problem, let's look at a straightforward code example that triggers this deprecation warning. This will help you understand precisely when and why it appears. The example involves creating a basic Plotly figure and then displaying it using st.plotly_chart with the width="content" parameter.

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 layout settings might not directly affect the st.plotly_chart width

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

In this code snippet, we first import the necessary libraries: plotly.graph_objects for creating the figure and streamlit for building the app. We then instantiate a go.Figure and add a simple Barpolar trace. The update_layout method is used to set some initial dimensions for the figure itself, though these are often overridden by Streamlit's display parameters. The crucial part is the last line: st.plotly_chart(fig, width="content"). Here, we are explicitly telling Streamlit to size the chart to fit its container's width.

Despite using a documented parameter (width="content"), running this code in Streamlit versions like 1.50.0 (as indicated in the original report) will likely result in the deprecation warning mentioned earlier. The warning appears because Streamlit's internal check for kwargs is being activated. The presence of width="content" is being misinterpreted as an arbitrary keyword argument, even though it's a recognized and intended parameter for controlling the chart's display size within the Streamlit framework. This behavior is particularly noticeable when you're not explicitly passing other keyword arguments to st.plotly_chart, making the warning seem out of place.

This reproducible example clearly demonstrates that the issue isn't about users trying to pass unsupported arguments. It's about a potential flaw in how Streamlit identifies and warns about deprecated kwargs usage. The expected behavior is that specifying a valid, documented parameter like width="content" should not trigger a deprecation warning related to general keyword arguments. The goal is to have a clean output without unnecessary warnings, especially when adhering to the documented API.

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

Let's clarify the distinction between what we anticipate and what's currently being observed. The expected behavior when working with st.plotly_chart is that you should be able to leverage its documented parameters without encountering extraneous warnings. Specifically, when you set width="content" or height="content", Streamlit should correctly interpret these as instructions to make the chart responsive to its container's width, and not as a signal of deprecated keyword argument usage.

The documentation for st.plotly_chart typically outlines parameters like use_container_width (which was a boolean) and more recently, width and height (which can accept string values like 'content' or numerical pixel values). The transition from use_container_width to width and height parameters was itself a move to provide more flexible control. Therefore, using these new parameters as described should be a smooth experience. The expectation is that Streamlit will gracefully handle these inputs, render the Plotly chart appropriately, and remain silent on the kwargs deprecation front.

The current behavior, however, presents a discrepancy. As reported, when st.plotly_chart is called with width="content", a deprecation warning related to variable keyword arguments is displayed. This 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," appears even when no other arbitrary kwargs are being passed. The function is essentially misinterpreting the width="content" argument as an example of the deprecated kwargs usage it aims to warn against.

This is a regression because, in previous versions of Streamlit, this functionality likely worked without generating such a warning. The update that introduced the kwargs deprecation warning seems to have inadvertently included documented parameters within its scope. This means that even though you are following the API's guidelines, you're receiving a warning that suggests you are not.

To reiterate, the config argument in st.plotly_chart is indeed the intended place for passing Plotly's own configuration options (like `{