Fixing Plotly Chart Deprecation Warnings In Streamlit

Dec 20, 2025 by Alex Johnson 54 views

Streamlit's `plotly_chart` and the Intriguing Kwargs Deprecation Warning

Hey there, fellow Streamlit enthusiasts! Have you ever been happily building your dashboard, adding some snazzy interactive plots using st.plotly_chart, only to be greeted by a rather stern deprecation warning? You look at your code, thinking, "But I'm not using any weird, extra keyword arguments! I'm sticking to the docs!" Well, you're not alone, and today we're diving deep into this head-scratcher.

The Case of the Unwanted Kwargs Warning

One of the most common and frankly annoying issues we've encountered lately revolves around the plotly_chart function in Streamlit. Specifically, when you try to control the dimensions of your Plotly charts using parameters like width="content" or height="content", a deprecation warning pops up. This warning, related to variable keyword arguments (kwargs), appears even when you're diligently using only the documented parameters and haven't explicitly passed any **kwargs yourself. It's like getting a warning for jaywalking when you're safely on the sidewalk! This unexpected behavior can be quite confusing, especially for developers who are new to Streamlit or trying to ensure their code is future-proof by adhering to best practices. The core of the issue lies in how Streamlit handles arguments passed to st.plotly_chart. While width and height are indeed legitimate parameters for controlling the chart's display, the internal workings of the function seem to be misinterpreting their presence, triggering the deprecation warning meant for unrecognised, arbitrary keyword arguments.

This isn't just a minor inconvenience; it can lead to a cascade of concerns. Developers might start second-guessing their use of perfectly valid parameters, potentially spending valuable time debugging or trying to find alternative (and possibly less intuitive) solutions. Furthermore, a flood of deprecation warnings, even if benign, can obscure genuinely important warnings, making it harder to maintain code health. The Streamlit team has been working hard to streamline the API and provide clear guidance, and this particular warning seems to be a hiccup in that process. It highlights the delicate balance between providing a flexible API and ensuring clarity and stability. The intent behind the **kwargs warning is to guide users towards using the config argument for Plotly-specific settings, but when documented parameters like width trigger it, the message becomes muddled. It's crucial to address this so that users can confidently use all documented features without unnecessary alerts.

Why Does This Happen? Let's Unpack the Code

The root cause of this peculiar warning seems to stem from a specific check within Streamlit's plotly_chart function. As reported, the following snippet is likely responsible:

if kwargs:
 show_deprecation_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."
 )

This conditional statement checks if there are any remaining kwargs after all explicitly defined parameters have been processed. The issue arises because, in certain versions of Streamlit (like 1.50.0 mentioned in the report), parameters like width="content" are not being correctly identified as explicit parameters but are instead being caught by this if kwargs: check. This leads to the deprecation warning being displayed even when you're using documented functionality. The warning itself is designed to encourage users to move Plotly-specific configurations into the config dictionary, which is the recommended way to pass settings directly to the underlying Plotly.js library. However, when parameters that control the Streamlit rendering of the chart, such as width and height, are misinterpreted as generic kwargs, the warning becomes misleading. It suggests that the user is doing something unsupported when, in fact, they are using a documented feature. This creates a disconnect between the intended warning message and its actual trigger, causing confusion and potential frustration for developers.

It's important to understand that Streamlit often acts as a wrapper or an enhancer for other libraries. In this case, it's integrating Plotly charts into a web application. Parameters like width and height in st.plotly_chart are controlling how Streamlit displays the chart within the app's layout, rather than being direct Plotly figure attributes. The warning, however, seems to be conflating these layout parameters with general Plotly configuration options that should indeed be passed via the config dictionary. This suggests a potential misalignment in how Streamlit is parsing and handling arguments for st.plotly_chart, where layout-related arguments are being mistakenly flagged as general keyword arguments that should be moved to config.

The Expected vs. Current Behavior: A Tale of Two Outcomes

When you're developing with Streamlit, you expect things to work as documented. For st.plotly_chart, the documentation clearly indicates that you can control the display dimensions using width and height parameters. Setting width="content" (or height="content") is a perfectly valid and useful way to make your charts adapt to the available space in your Streamlit app. Therefore, the expected behavior is that using these documented parameters should not trigger any deprecation warnings. The chart should render, filling the content area as specified, and your console should remain clean.

However, the current behavior, as observed in certain Streamlit versions, is quite different. Despite using width="content" correctly, the application throws a deprecation warning: "Variable keyword arguments for st.plotly_chart have been deprecated... Use the config argument instead." This warning appears because the internal logic of st.plotly_chart is incorrectly identifying the width parameter as an unhandled keyword argument, even though it's a legitimate and documented parameter for controlling the chart's display within the Streamlit framework. This creates a discrepancy where the user is following the documentation, but the tool signals a potential error or outdated practice. This can be particularly disheartening as it undermines confidence in the library's stability and documentation accuracy. It's a regression because, in previous versions, this functionality worked without generating such warnings, indicating a change in Streamlit's internal argument parsing or handling that has inadvertently broken this specific use case.

This discrepancy is crucial to resolve because it impacts the developer experience. A clean console output is invaluable for spotting actual issues. When legitimate parameters trigger warnings, it leads to noise and can obscure real problems. It also forces developers to either ignore the warning (which is generally bad practice) or attempt workarounds that might be less efficient or harder to maintain. The goal of Streamlit is to make app development smooth and intuitive, and this warning acts as a roadblock to that experience. The expectation is that Streamlit's API will consistently respect its own documentation, and any deviation, like this kwargs warning for valid width/height arguments, needs to be addressed swiftly.

Is This a Regression? Yes, It Appears So!

The user's report explicitly states, "Yes, this used to work in a previous version." This is the hallmark of a regression. A regression occurs when a piece of software that previously functioned correctly begins to malfunction after a change, typically an update or a new release. In this context, the ability to use width="content" or height="content" with st.plotly_chart without triggering a kwargs deprecation warning was a feature that worked in older versions of Streamlit. With the introduction of changes related to keyword arguments and the config parameter in newer versions (specifically, the check if kwargs:), this functionality has been inadvertently broken.

This is a significant point because it means the issue isn't a fundamental misunderstanding of how plotly_chart should work, but rather a change in Streamlit's implementation that has caused a previously supported feature to behave unexpectedly. Regressions can be particularly frustrating because they can disrupt existing, working applications without any apparent user error. Developers might update Streamlit to take advantage of new features or security patches, only to find that their established workflows are now generating warnings or errors. Identifying this as a regression is key for the Streamlit development team to pinpoint the exact code changes that led to this behavior and implement a fix. It signals that the change was likely unintended and needs to be reverted or adjusted to restore the previous, correct functionality. The aim is always to move forward, adding new capabilities and improving the user experience, but regressions represent a step backward that requires immediate attention to maintain the library's reliability and the trust of its users.

Reproducible Code Example: Seeing is Believing

To truly understand and verify this issue, having a clear, runnable code snippet is essential. The provided example is concise and effectively demonstrates the problem:

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")

Let's break down why this example triggers the warning. We import the necessary libraries, plotly.graph_objects for creating the figure and streamlit for displaying it. A simple Barpolar chart is created. Crucially, fig.update_layout(width=500, height=360) sets some initial dimensions for the Plotly figure itself. However, the line st.plotly_chart(fig, width="content") is where the magic (or in this case, the warning) happens. Here, width="content" is passed as an argument to Streamlit's plotly_chart function. This argument tells Streamlit to adjust the chart's width to fill the available content area of the Streamlit app's layout. According to the Streamlit documentation, this is a valid and intended use. However, as we discussed, recent versions of Streamlit seem to misinterpret this argument, leading it to be treated as a general kwargs that should have been part of the config dictionary. Consequently, the if kwargs: check inside st.plotly_chart evaluates to true, firing off the deprecation warning about variable keyword arguments, even though width="content" is a documented parameter.

This example is powerful because it's minimal. It isolates the specific action that causes the warning, removing any potential complexities from the plot itself or other parts of the Streamlit app. By running this code in an environment with the affected Streamlit version (like 1.50.0), users can reliably reproduce the deprecation warning. This is invaluable for debugging and for Streamlit developers to confirm the bug. It's a clear demonstration that the issue isn't with how the Plotly chart is constructed, but rather how Streamlit's plotly_chart function processes its own arguments, particularly when width or height are set to special string values like 'content'.

What Should Happen: The Ideal Scenario

In an ideal world, using Streamlit's plotly_chart should be seamless, especially when adhering to the documented parameters. The expected behavior in this scenario is straightforward: the st.plotly_chart function should accept the width="content" argument without any fuss. This argument is designed to provide a responsive and user-friendly experience, allowing charts to dynamically adjust their size based on the container they are placed within. When this works correctly, the chart renders beautifully, fitting snugly within the app's layout, and your console remains free of unnecessary warnings. It's the kind of smooth interaction that makes Streamlit such a joy to use for building data applications.

This means that the internal checks within st.plotly_chart should correctly identify width and height (when used with specific string values like 'content') as recognized parameters for controlling the Streamlit rendering of the chart. They should not be mistakenly flagged as general kwargs that need to be moved to the config dictionary. The config parameter is intended for passing settings that are directly interpreted by the Plotly.js library itself (e.g., config={'displayModeBar': False}). Arguments like width and height are part of Streamlit's API for managing the embedding and display of the chart within the Streamlit application's structure. Therefore, the expectation is that Streamlit's argument parsing logic correctly distinguishes between these two types of parameters. A clean execution, without the kwargs deprecation warning, is the desired outcome, confirming that the documented parameters are working as intended and that the library is behaving predictably and reliably. This ensures developers can focus on their data and visualizations, rather than troubleshooting warnings generated by standard usage.

Debugging Information: A Snapshot of the Environment

Understanding the environment in which an issue occurs is crucial for effective debugging. The provided debugging information gives us a clear picture:

Streamlit version: 1.50.0 - This is a key piece of information, as it pinpoints the specific version where the behavior was observed. Knowing this allows developers to check release notes for changes introduced around this version and to test the issue against both earlier and later versions to confirm it's a regression introduced in 1.50.0.
Python version: 3.14.2 - While Python versions can sometimes influence library behavior, this particular issue seems more directly tied to Streamlit's internal logic. However, it's good practice to note it.
Operating System: MacOs 26.1 - Operating system details can be relevant for issues related to file paths, system calls, or frontend rendering, but are less likely to be the primary cause here.
Browser: Chrome - Similar to the OS, the browser can impact frontend rendering, but the warning itself is a backend/Python-level message originating from Streamlit.

This information collectively suggests that the problem is likely confined to the Streamlit library's codebase, specifically how it handles arguments in the st.plotly_chart function in version 1.50.0. The fact that it's a consistent combination of Streamlit and Python versions, on a common OS and browser, means it's a reproducible issue for many users. The absence of browser-specific or OS-specific anomalies strengthens the case for an internal Streamlit bug related to argument parsing. It guides the debugging effort directly towards the Python code of the Streamlit library, particularly the plotly_chart component and its handling of keyword arguments and dimension settings.

Moving Forward: Towards a Cleaner `plotly_chart` Experience

This issue, while seemingly small, highlights the importance of precise argument handling and clear communication within software libraries. The kwargs deprecation warning in st.plotly_chart when using width="content" is a prime example of how a well-intentioned feature can lead to user confusion if not implemented carefully. It's a regression that disrupts the expected behavior and adds unnecessary noise to the development process.

The fix for this issue would involve adjusting Streamlit's argument parsing logic within st.plotly_chart. The function needs to correctly identify and handle width and height parameters (especially when set to values like 'content') as explicit, documented arguments, rather than misclassifying them as general kwargs. This would prevent the misleading deprecation warning from being shown.

For users encountering this, the immediate workaround is often to ignore the warning if the functionality is otherwise working, or to check for updates to Streamlit, as bug fixes are typically released to address such regressions. Ultimately, the goal is to ensure that documented features work as expected and that deprecation warnings are reserved for genuinely outdated practices.

If you're looking to learn more about Streamlit and its capabilities, or about Plotly for creating stunning visualizations, here are some excellent resources:

Streamlit Documentation: Your go-to source for all things Streamlit, including detailed explanations of components and parameters.
Plotly Python Graphing Library: Explore the vast possibilities of interactive charting with Plotly's extensive documentation and examples.