Fix Plotly Chart 'width=content' Deprecation Warning

Navigating the nuances of web development can sometimes feel like a treasure hunt, and recently, Streamlit users have stumbled upon a peculiar warning message. When deploying interactive charts with Plotly using Streamlit's st.plotly_chart function, and specifically when trying to set the width or height attribute to "content", a deprecation warning pops up. This message suggests that variable keyword arguments (kwargs) are being deprecated. Oddly, this warning appears even when developers aren't explicitly using variable keyword arguments and are sticking to the documented parameters. This might leave you scratching your head, wondering why you're seeing a deprecation notice when your code seems perfectly fine. Let's dive into why this happens and how to address it, ensuring your Streamlit apps run smoothly and without those nagging warnings.

Understanding the st.plotly_chart Deprecation Warning

The core of the issue lies within how Streamlit handles arguments passed to st.plotly_chart. The warning specifically states: "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 when you use arguments like width="content" or height="content". While these arguments are intended to make your charts dynamically adjust to their container, Streamlit's internal logic interprets their usage in a way that flags them under the broader deprecation of arbitrary kwargs.

Historically, st.plotly_chart might have accepted a wider range of arguments directly, and as the library evolves, there's a push to consolidate configuration options. The config argument was introduced as the central place to manage all Plotly-specific settings, including layout adjustments. The deprecation warning is essentially Streamlit's way of nudging developers towards this more structured approach. Even though width="content" is a valid and useful parameter for responsive design, Streamlit's current implementation flags it as if it were an unstructured kwargs being passed.

This can be particularly confusing because width and height are documented parameters for controlling the chart's dimensions. The warning implies that you are passing something unexpected, when in reality, you are using a feature as intended. This scenario often arises when libraries update their internal argument parsing or when features are transitioned to new API endpoints. The goal is to maintain backward compatibility while guiding users toward the preferred, more robust methods. In this case, the width="content" functionality is still present and works, but it comes with an unnecessary warning.

It's important to remember that deprecation warnings are not bugs in the traditional sense; they are signals from the developers about future changes. However, an unwanted warning can clutter logs, obscure actual errors, and make the development process feel less polished. The good news is that this particular warning can be managed by understanding the underlying mechanism and applying the recommended solution.

The Root Cause: Argument Handling in Streamlit

The st.plotly_chart function in Streamlit is designed to be a versatile tool for embedding interactive Plotly charts within your web applications. When you pass arguments like width, height, or other Plotly-specific configurations directly to st.plotly_chart, Streamlit processes them. In recent versions, Streamlit has been refining its argument handling, aiming for greater clarity and consistency. A key part of this refinement has been the introduction of the config argument as the primary way to pass Plotly-related configurations.

The deprecation warning you're encountering stems from this architectural shift. The code snippet causing the warning checks if any kwargs are present. The intent behind this check is to catch any arguments passed that are not explicitly defined parameters of st.plotly_chart itself. However, it seems the width and height parameters, when set to values like "content", are being caught by this kwargs check, even though they are intended for direct use.

This might happen because the width and height parameters, in some contexts, might be treated more like Plotly layout attributes rather than direct Streamlit function arguments. Streamlit's internal mechanism for distinguishing between its own arguments and those meant for the underlying Plotly figure or its configuration can sometimes be a bit finicky. When width="content" is passed, Streamlit's argument parser might not correctly identify it as a supported direct argument and instead lumps it into the general kwargs category.

This is a common challenge in library development: ensuring that features intended for direct use are not mistakenly flagged as deprecated or unsupported. The developers are working to ensure that documented and functional parameters like width="content" are correctly handled and do not trigger the kwargs deprecation warning. The goal is to provide a seamless experience where users can leverage the full power of Plotly within Streamlit without encountering confusing or unnecessary alerts.

The Solution: Embracing the config Argument

Streamlit's recommended approach to resolve this kwargs deprecation warning when using st.plotly_chart is to leverage the config argument. This argument is specifically designed to accept a dictionary of Plotly configuration options. Instead of passing width and height directly as arguments to st.plotly_chart, you should pass them within the config dictionary.

Here's how you would modify the reproducible code example to adhere to this best practice:

import plotly.graph_objects as go
import streamlit as st

fig = go.Figure()
fig.add_trace(go.Barpolar(r=[1], theta=[0], width=[120]))
# Update layout for figure dimensions if needed, but width/height for chart
# should be handled by st.plotly_chart's config.
# fig.update_layout(width=500, height=360)

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

In this corrected code, width="content" is no longer passed as a direct keyword argument to st.plotly_chart. Instead, it's included in the config dictionary. This tells Streamlit that you are providing a Plotly-specific configuration option, and it bypasses the kwargs check that was causing the deprecation warning.

Why does this work? The config argument is explicitly designed to handle Plotly's configuration parameters. By routing these parameters through config, you are signaling to Streamlit that you are using the intended mechanism for Plotly customization. This aligns with Streamlit's development philosophy of centralizing configuration options and provides a cleaner, more maintainable way to manage your charts.

This approach not only silences the deprecation warning but also makes your code more readable and future-proof, as it follows the recommended API usage. When working with Streamlit and Plotly, always check the documentation for the most current and recommended ways to pass configurations, as the library is constantly being updated to improve user experience and functionality.

Why the Change? Enhancing Robustness and Clarity

The transition towards using the config argument for Plotly chart configurations in Streamlit is a deliberate step aimed at improving the overall robustness and clarity of the library. As Streamlit grows and integrates with more powerful visualization libraries like Plotly, maintaining a clean and consistent API becomes increasingly important. Passing configuration options directly as kwargs to st.plotly_chart could lead to ambiguity, especially as Plotly itself offers a vast array of configuration settings.

By introducing the config dictionary, Streamlit provides a dedicated namespace for all Plotly-related settings. This separation helps prevent potential conflicts between Streamlit's own arguments and Plotly's internal parameters. It also makes it easier for developers to understand where to look for specific chart configurations. If you need to adjust Plotly's behavior, appearance, or interactivity, the config dictionary is the go-to place.

This move towards a more structured configuration system also prepares Streamlit for future updates. As Plotly evolves and introduces new features or configuration options, having a centralized config argument makes it easier for Streamlit to adapt and expose these new capabilities without breaking existing code or introducing a messy API. It allows for a cleaner mapping between Streamlit's component and the underlying Plotly object.

Furthermore, the config argument can accept a wide range of Plotly settings, not just dimensions. This includes options for enabling or disabling responsiveness, setting tooltips, controlling interactivity modes, and much more. By consolidating these options, Streamlit encourages developers to explore the full potential of Plotly within a well-defined framework.

While the deprecation warning might seem like a minor annoyance, it's a signal that Streamlit is actively working to provide a more streamlined and powerful experience for its users. Embracing the config argument is not just about silencing a warning; it's about adopting the best practices that will lead to more maintainable, scalable, and robust Streamlit applications.

Conclusion: A Smoother Path for Interactive Visualizations

In conclusion, the deprecation warning encountered when using width="content" (or height="content") with st.plotly_chart in Streamlit is a consequence of the library's ongoing efforts to refine its argument handling and encourage best practices. While the functionality itself remains valuable for creating responsive charts, the way it was passed triggered an internal check designed to flag unstructured kwargs.

By migrating these specific width and height settings into the config dictionary, you effectively resolve the warning. This approach aligns with Streamlit's recommended pattern for managing Plotly configurations, ensuring that your code is not only free of deprecation notices but also more robust and easier to maintain in the long run. It’s a small change that makes a significant difference in the clarity and polish of your Streamlit applications.

Moving forward, always refer to the official Streamlit documentation for the latest guidance on using st.plotly_chart and its configuration options. This will help you stay ahead of potential changes and leverage the full power of interactive visualizations in your data science projects.

For further exploration into interactive charting and data visualization best practices, you might find these resources helpful:

• Check out the official Plotly.js Documentation for a deep dive into all available Plotly configurations.
• Explore the Streamlit Documentation for the latest updates and examples on integrating various components, including charts.