Streamlit Plotly Chart: Fix Kwargs Deprecation Warning

Have you ever been happily charting away in Streamlit, only to be met with a mysterious kwargs deprecation warning? It’s a common hiccup, especially when you’re trying to get your plotly_chart to play nice with different widths. You’re not alone, and thankfully, it’s usually a simple fix or a misunderstanding of how Streamlit handles chart arguments. Let's dive into what this warning means and how to resolve it so you can get back to creating awesome visualizations.

Understanding the "kwargs deprecation warning"

When you see a message 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.", it’s Streamlit telling you about a change in how it expects you to pass certain types of arguments to the plotly_chart function. kwargs, short for keyword arguments, are essentially **named parameters** you pass to a function. In the context of st.plotly_chart, Streamlit used to allow you to pass various arguments directly, like width, height, or other Plotly-specific configurations, as direct keyword arguments.

However, as libraries evolve, so do their APIs. Streamlit noticed that users were often passing arguments that were intended for the underlying Plotly figure itself, or for controlling the chart's display within Streamlit. To make things clearer and more robust, they decided to consolidate these configuration options into a single config parameter. This means that instead of passing width='content' directly to st.plotly_chart, you should now pass it within the config dictionary. This change aims to prevent potential conflicts and make the API more predictable.

Why the deprecation warning, then? It’s a way for Streamlit to gently nudge developers towards the new, preferred way of doing things without breaking existing applications immediately. They provide a grace period where the old method still works, but you get a warning. Eventually, in a future version, they might remove support for passing these arguments directly, and your app could break if you haven’t updated. So, while it might seem like a minor annoyance now, it’s a signal to adapt your code for future compatibility.

Why is width="content" Causing This Warning?

The core of the issue lies in how Streamlit interprets arguments passed to st.plotly_chart. When you use st.plotly_chart(fig, width="content"), you are passing width="content" as a keyword argument. Streamlit's internal logic checks for these keyword arguments. If it detects arguments that are now intended to be part of the config object (like width for controlling the chart's display dimensions), it triggers the deprecation warning because it's using the older method of argument handling.

It’s important to note that width="content" isn't directly a Plotly figure argument; it’s a Streamlit-specific instruction on how to render the chart. Plotly itself doesn’t inherently understand the concept of "content" width in the same way a web framework might. Streamlit intercepts this and applies it to the container holding the Plotly chart. Because this was previously handled as a direct keyword argument, and Streamlit is now guiding users to use the config parameter for such display-related settings, the warning appears.

This happens even if you aren't explicitly passing any other variable keyword arguments. The warning is triggered by the mere presence of arguments like width or height when passed directly to st.plotly_chart, signaling that these should be managed differently. The goal is to streamline the process and ensure that arguments meant for Plotly are passed to Plotly, and arguments for Streamlit's rendering are handled by Streamlit's configuration system.

Reproducible Code Example and Steps to Reproduce

Let's look at the code that triggers this warning and how to fix it. The provided example is a perfect illustration:

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. Install necessary libraries: Ensure you have streamlit and plotly installed (pip install streamlit plotly).
2. Create a Python file: Save the code above into a file (e.g., app.py).
3. Run the Streamlit app: Open your terminal, navigate to the directory where you saved the file, and run streamlit run app.py.

When you run this code, you will see the Plotly chart displayed, but in your Streamlit terminal output or logs, you'll encounter the deprecation warning related to kwargs. This confirms that even with a seemingly valid argument like width="content", Streamlit flags it as deprecated.

Expected vs. Current Behavior

Expected Behavior:

Ideally, when using st.plotly_chart with arguments like width="content" (which is documented and intended for controlling the chart's responsive behavior within Streamlit), it should not trigger a deprecation warning. The transition from use_container_width to the width argument within config is meant to be smooth. Therefore, passing documented parameters for chart display should work seamlessly without warnings about deprecated kwargs, especially when no other variable keyword arguments are being passed.

Current Behavior:

As demonstrated by the reproducible code, the current behavior is that providing width="content" directly to st.plotly_chart does trigger the kwargs deprecation warning. This is because Streamlit's internal check for kwargs is catching this argument and, under the new system, it's flagged as something that should ideally be handled within the config parameter. The warning message specifically points out that "Variable keyword arguments for st.plotly_chart have been deprecated," and width is being treated as one of those arguments.

This is indeed a regression because, in previous versions of Streamlit, this functionality likely worked without issuing such a warning. Users who are updating their Streamlit applications might be surprised to see these warnings pop up, even when their code is functionally correct according to the documentation for display-related parameters.

How to Fix the st.plotly_chart kwargs Warning

The solution is straightforward and involves adhering to Streamlit's recommended way of configuring chart display: using the config parameter. Instead of passing width="content" directly, you should encapsulate it within a dictionary passed to config.

Here's how to modify the reproducible code example:

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)

# The fix: Pass width within the config dictionary
st.plotly_chart(fig, config={"width": "content"})

Explanation of the Fix:

• config={"width": "content"}: We've replaced width="content" with config={"width": "content"}. The config parameter is a dictionary where you can pass various configuration options for the Plotly chart. In this case, we're telling Streamlit to use a width of "content" for the chart's display container.

This approach correctly directs the width setting to Streamlit's rendering mechanism via the designated config parameter, thereby avoiding the kwargs deprecation warning. It aligns with Streamlit's evolving API design, ensuring your applications are future-proof.

Why this works:

Streamlit's plotly_chart function is designed to accept a config argument. This argument is a dictionary that allows you to pass specific settings related to how the chart should be rendered or behave within the Streamlit app. Arguments like width, height, use_container_width (which was previously used), and other display-related configurations are now expected to be placed inside this config dictionary. By moving width="content" into config, you are telling Streamlit precisely where to look for this setting, and it no longer flags it as an unexpected or deprecated direct keyword argument.

This change is not just about avoiding a warning; it's about adopting the standardized way Streamlit wants you to handle chart configurations. As Streamlit continues to develop, relying on the config parameter for these types of settings will ensure better compatibility and access to future features.

Conclusion

The kwargs deprecation warning when using st.plotly_chart with parameters like width="content" might seem confusing at first, but it’s a sign of Streamlit maturing and refining its API. The solution is simple: encapsulate display-related arguments within the config dictionary. By updating your code to use config={"width": "content"} (or similar configurations), you can eliminate the warning, ensure your Streamlit applications are up-to-date, and maintain compatibility with future releases.

This adjustment is a small step that contributes to building more robust and maintainable data applications. As you continue to develop with Streamlit, always keep an eye on the official documentation for the latest best practices and API changes.

For more in-depth information on Plotly configurations within Streamlit, you can refer to the official Streamlit documentation on Streamlit components and Plotly integration. For Plotly specific configurations, the Plotly.js documentation is an invaluable resource.