Fixing Plotly Chart Deprecation Warnings In Streamlit

Ever been happily coding away, building a beautiful interactive chart with Streamlit and Plotly, only to be interrupted by a cryptic deprecation warning? You know the one: it mentions kwargs and suggests using config instead. It can be quite frustrating, especially when you feel like you're following the documentation correctly. Well, you're not alone! Many users have encountered this, and it stems from a specific behavior when using st.plotly_chart with arguments like width='content' or height='content'. Let's unpack this, understand why it's happening, and how to navigate it smoothly.

Understanding the kwargs Deprecation Warning

The core of the issue lies in how Streamlit handles arguments passed to st.plotly_chart. When you use parameters like width='content' or height='content', Streamlit's internal mechanisms might interpret these as variable keyword arguments (kwargs). This is particularly true if the underlying Plotly library or Streamlit's own argument parsing has evolved. The deprecation warning is designed to signal a shift in how configuration options should be passed, encouraging developers to use the dedicated config argument for Plotly-specific settings rather than relying on potentially ambiguous kwargs.

This warning, often seen as:

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 appear even when you're not explicitly passing any other keyword arguments beyond the documented ones. This is because Streamlit's internal processing, for reasons of backward compatibility or future-proofing, might bundle certain arguments, like width or height when set to 'content', into a kwargs structure before they are passed to the plotting function. The warning, therefore, acts as a heads-up that this internal handling might change, and it's best practice to use the config parameter moving forward for any Plotly-specific configurations.

Why does this happen? The st.plotly_chart function is a wrapper that takes a Plotly figure and displays it within your Streamlit app. It also accepts several Streamlit-specific arguments to control how the chart is rendered, such as width, height, use_container_width, and theme. Historically, these might have been passed more directly. However, as libraries evolve, there's a push towards more structured configuration. The config argument in st.plotly_chart is intended to be a dictionary where you can pass Plotly.js configuration options. When you use width='content', Streamlit interprets this as a request to dynamically size the chart to fit its container. Internally, to manage these display options alongside potential Plotly configurations, Streamlit might group them. If this grouping results in arguments being passed via a kwargs mechanism that the warning system flags, you'll see the message.

It's a bit like a chef having a specific drawer for spices (the config argument) but sometimes putting a few extra seasonings in a general 'extra ingredients' box (kwargs). The warning is telling you to put all your seasonings in the spice drawer from now on to avoid confusion.

Reproducible Code Example and Steps to Reproduce

Let's look at a practical example that triggers this warning. The following code snippet, which is quite straightforward, demonstrates the scenario:

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")

Steps to Reproduce:

1. Ensure you have Streamlit and Plotly installed:

   pip install streamlit plotly
   

2. Save the code: Save the Python code above into a file, for instance, app.py.
3. Run the Streamlit app: Open your terminal, navigate to the directory where you saved app.py, and run:

   streamlit run app.py
   

4. Observe the output: When the Streamlit app loads in your browser, you should see the Plotly chart displayed. Crucially, look at your terminal where you ran the Streamlit command. You will notice the deprecation warning regarding kwargs being printed there, even though you only explicitly used the width='content' argument.

This reproducible example clearly shows that the warning appears simply by using a documented parameter (width='content') with st.plotly_chart, without any other arbitrary keyword arguments being passed.

Expected vs. Current Behavior

The expected behavior, according to the Streamlit documentation and the general understanding of how such parameters should work, is that using documented arguments like width='content' should not trigger a deprecation warning related to kwargs. The documentation often guides users to width or height for controlling chart dimensions, and use_container_width=True (which is often implied or achieved by width='content') is a standard way to make charts responsive. Therefore, encountering a kwargs deprecation warning in this context is unexpected and indicates a potential mismatch between the library's internal implementation and its user-facing documentation or expected behavior.

Expected Behavior:

• When st.plotly_chart(fig, width='content') is used, the chart should render correctly, adjusting its width to fit the Streamlit container.
• No deprecation warnings related to kwargs should be displayed in the console or the Streamlit app's debug logs.
• The user experience should be seamless, with developers able to control chart dimensions using standard parameters without unexpected warnings.

Current Behavior:

• The chart renders as expected, adjusting its width to fit the container.
• However, a deprecation warning appears in the console:

  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 specifically when width='content' (or similarly height='content') is passed as an argument to st.plotly_chart, even when no other unintended kwargs are present.

This discrepancy suggests that Streamlit's internal handling of these specific width/height arguments might be inadvertently falling into a category that triggers the kwargs deprecation warning, which was intended for a different use case (i.e., passing arbitrary, undocumented keyword arguments directly to Plotly functions).

Is this a Regression?

Yes, this is indeed a regression. In previous versions of Streamlit, using parameters like width='content' or height='content' with st.plotly_chart did not result in a kwargs deprecation warning. Users could confidently set these parameters to control the layout of their charts without receiving this specific warning. The introduction of this warning in this context indicates a change in Streamlit's internal argument processing or warning logic that has unintended consequences for standard usage patterns.

This regression is problematic because:

1. It creates noise: Developers might see the warning and spend time investigating it, thinking they've made a mistake or are using an unsupported feature, when in reality, they are using the API as documented.
2. It can obscure real issues: If there are other, genuine kwargs deprecation warnings in a larger application, this spurious warning could make them harder to spot.
3. It reduces confidence: Users might become hesitant to use seemingly standard features if they trigger warnings, fearing that these features might be removed or changed unexpectedly.

Understanding that this is a regression helps in pinpointing the specific changes in Streamlit's codebase that led to this behavior. It implies that a recent update might have refactored how arguments are passed or checked, and this particular scenario wasn't accounted for in the testing or implementation of the warning system.

Debug Info

To help diagnose this issue further, here's the debug information from the environment where the warning was observed:

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

This information provides a snapshot of the environment, which is crucial for identifying potential version-specific bugs or compatibility issues. While Streamlit 1.50.0 is not the very latest, it's a recent enough version that such issues might have been introduced or persisted.

Conclusion and Moving Forward

The kwargs deprecation warning when using st.plotly_chart with width='content' or height='content' is a usability issue that stems from Streamlit's internal argument handling. While the warning's intention is to guide users towards the config parameter for Plotly-specific options, it's currently being triggered by standard Streamlit layout parameters, acting as a regression and causing unnecessary confusion.

What can you do?

• Report the issue: As has been done here, reporting such issues to the Streamlit development team is vital. Providing a clear, reproducible example like the one above allows maintainers to investigate and fix the behavior.
• Use use_container_width=True: As an alternative, you can often achieve the same responsive width behavior by using st.plotly_chart(fig, use_container_width=True). This parameter is specifically designed for controlling width relative to the container and might not trigger the same kwargs warning.
• Monitor Streamlit updates: Keep an eye on Streamlit release notes and issue trackers for updates related to st.plotly_chart and argument handling. A fix for this specific issue is likely to be included in a future release.

While waiting for an official fix, using use_container_width=True is a good workaround. It achieves the desired responsive chart behavior without generating the confusing deprecation warning. Remember, the goal is to build clear, functional, and maintainable Streamlit applications, and understanding these nuances helps us achieve that.

For more information on Streamlit and Plotly integration, you can refer to the official documentation:

• Streamlit Documentation: For general Streamlit usage and components, visit Streamlit Docs.
• Plotly Python Library: To understand Plotly figure creation and layout options, check out the Plotly Python Docs.

By staying informed and utilizing workarounds when necessary, we can continue to create dynamic and engaging data visualizations with Streamlit.