Streamlit Plotly Chart Width Error: Deprecation Warning

If you've been working with Streamlit and noticed a perplexing deprecation warning when trying to set the width or height of your plotly_chart elements, you're not alone. Many users have encountered this, especially when using values like "content" for these parameters. This article aims to shed light on why this happens and what the expected behavior should be, ensuring you can continue to create stunning interactive plots without unnecessary alerts. We'll dive into the specifics of this warning, providing a clear explanation and a reproducible code example to help you understand the issue.

The plotly_chart Keyword Argument Conundrum

The core of the issue lies in how Streamlit handles keyword arguments (kwargs) passed to its st.plotly_chart function. Recently, there have been changes and updates to how these arguments are managed, particularly concerning the deprecation of certain parameters. The intention behind these changes is to streamline the API and guide users towards more robust and future-proof ways of configuring their plots. However, in the process, a warning message has started appearing that might be a bit misleading for some users. The warning states that "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 even when you're not explicitly passing any arbitrary keyword arguments. Instead, you might be using well-documented parameters like width="content" or height="content" which are intended for controlling the plot's dimensions. It appears that the warning mechanism is catching these valid arguments as if they were undefined kwargs, leading to confusion and an unnecessary alert in your Streamlit application. This can be particularly frustrating when you're simply trying to make your charts responsive or fit them nicely within your app's layout. The goal of this article is to clarify that using parameters like width and height with specific values should not trigger this kwargs deprecation warning, as they are indeed documented and intended for use.

Reproducible Code Example: Triggering the Warning

To help you understand and replicate the behavior, here's a straightforward Python code snippet using Streamlit and Plotly. This example creates a simple Plotly figure and then displays it using st.plotly_chart, explicitly setting the width parameter to "content". When you run this code in a Streamlit environment with a version that exhibits this behavior, you should observe the deprecation warning in your application's output. Pay close attention to the warning message and its context. It's crucial to have a reproducible example to pinpoint the exact cause and to confirm that the issue isn't specific to your local setup or a more complex application. The code provided is designed to be minimal and focused, isolating the st.plotly_chart function and its parameters. By running this, you can directly see the warning emerge, allowing for a more concrete understanding of the problem. We've included a basic Plotly figure with a Barpolar trace, which is often used for circular data visualization. The update_layout method is used to set some basic dimensions, though these are often overridden by the Streamlit parameters. The key part is the st.plotly_chart(fig, width="content") line, which is where the unexpected warning originates. This example serves as a baseline for discussion and potential debugging, ensuring that everyone is on the same page regarding the observed behavior and its implications for Streamlit application development.

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. You can do this via pip:

   pip install streamlit plotly
   

2. Save the code: Save the Python code example above into a file named app.py (or any other .py file).
3. Run the Streamlit app: Open your terminal or command prompt, navigate to the directory where you saved the file, and run the command:

   streamlit run app.py
   

4. Observe the output: When the Streamlit application loads in your browser, look for a deprecation warning message in the console output or directly within the Streamlit app interface, related to kwargs in st.plotly_chart.

This sequence of steps should reliably reproduce the warning, even if you're not explicitly passing any extraneous keyword arguments beyond the documented width parameter.

Expected vs. Current Behavior: What Should Happen?

The expected behavior when using st.plotly_chart with the width argument set to "content" is that it should function as intended without raising any deprecation warnings. The Streamlit documentation clearly indicates that parameters like width and height are supported for controlling the size of the displayed chart. These parameters are designed to allow developers to make their plots adapt to the available space in the Streamlit app, either by filling the container or by taking on the intrinsic width of the plot itself. Therefore, providing width="content" should be a valid and documented way to set the chart's width, and it should not be flagged as an unrecognized or deprecated keyword argument. The current behavior, however, is that this valid usage does trigger a deprecation warning related to kwargs. This suggests a potential issue in Streamlit's internal handling of arguments passed to st.plotly_chart. The warning message implies that all additional keyword arguments are being treated as generic kwargs that are subject to deprecation, rather than being recognized as specific, documented parameters like width and height. This discrepancy between the intended functionality and the observed warning is the crux of the problem.

Understanding the Deprecation Warning

The deprecation warning, specifically: "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 a crucial piece of information, but its application in this context seems to be a misfire. Historically, Streamlit might have allowed a broader range of direct keyword arguments for Plotly charts. As Plotly's own configuration options grew, and to provide a more structured approach, Streamlit introduced the config argument. This config argument is a dictionary designed to pass Plotly-specific configurations, including aspects like layout, interactivity, and other display settings that are native to Plotly. The deprecation warning is intended to guide users away from passing these Plotly-specific settings directly as keyword arguments to st.plotly_chart and instead funnel them through the config dictionary. This promotes clarity and ensures that Streamlit doesn't have to constantly adapt its API to every single new configuration option that Plotly might introduce. However, the issue arises because parameters like width and height (especially with values like "content") are Streamlit-specific arguments for controlling the display of the chart within the Streamlit app, rather than Plotly's internal configuration. It seems that the warning's trigger condition is too broad and incorrectly identifies these valid Streamlit-level display arguments as deprecated kwargs. This is a common challenge in software development where a mechanism designed for one purpose can inadvertently affect other, valid functionalities. The fix likely involves refining the logic that checks for kwargs to differentiate between true, undocumented keyword arguments and documented Streamlit parameters like width and height.

Is This a Regression?

Yes, this behavior is considered a regression. Users previously reported that setting the width parameter of st.plotly_chart to "content" worked without any deprecation warnings. The fact that it now triggers a warning, even when using documented parameters, indicates a change in the expected functionality or the warning system itself. Regressions occur when a feature that previously worked correctly stops working or behaves unexpectedly in a newer version of the software. In this case, the introduction or modification of the kwargs handling in st.plotly_chart has inadvertently broken the expected behavior for controlling chart dimensions using the width parameter. This is why the issue has been flagged as a regression, highlighting the need for a fix to restore the previous, correct functionality. Understanding that it's a regression helps prioritize the issue, as it impacts existing applications that might have relied on this feature working without warnings.

Debug Information Summary

To aid in diagnosing and resolving this issue, here's a summary of the relevant debug information provided:

• 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 where the issue is being observed. Version 1.50.0 of Streamlit is notable, as specific changes to argument handling might have been introduced around this period. The Python version and OS are standard for many development environments, and Chrome is a widely used browser, suggesting the issue is not likely tied to obscure environment configurations. The key takeaway from this debug info is the specific Streamlit version, which is essential for developers looking into the codebase to pinpoint the exact commit or change that introduced this behavior. If you are experiencing this issue, ensuring you are using a compatible version of Python and Streamlit, and testing across different browsers, can help narrow down potential causes.

Conclusion: Towards a Smoother Plotting Experience

This detailed look into the st.plotly_chart kwargs deprecation warning reveals a common scenario in software development: a change intended to improve one aspect of the API inadvertently causes issues with existing, valid functionality. The warning about deprecated kwargs is a good initiative to guide users towards using the config argument for Plotly-specific settings. However, its current implementation seems to be overly broad, flagging documented Streamlit-level display parameters like width="content" as problematic. This behavior is a regression, as it disrupts the expected workflow for controlling chart dimensions. By understanding the root cause and having a reproducible example, the Streamlit development team can more effectively address this issue. The expectation is that using documented parameters for controlling chart size should not trigger these warnings, leading to a cleaner and more intuitive user experience when integrating interactive Plotly charts into Streamlit applications.

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

• Streamlit Documentation: Explore the official Streamlit documentation for detailed information on using st.plotly_chart and its various parameters.
• Plotly Documentation: For in-depth details about Plotly's configuration options, visit the Plotly documentation.