Streamlit Plotly Chart: Fixing Deprecation Warnings

Have you ever been happily coding away in Streamlit, building out some amazing data visualizations with Plotly, only to be greeted by a cryptic deprecation warning? It can be a bit jarring, especially when you're sure you're using the tool as intended. A common culprit for this is the st.plotly_chart function, specifically when you try to adjust the width or height of your charts using arguments like width="content". You might be thinking, "But I'm not passing any weird keyword arguments! I'm just using what the documentation says!" Well, you're not alone, and it turns out there's a subtle reason behind this warning that might not be immediately obvious. Let's dive into what's happening and how to get rid of that pesky warning so you can focus on what truly matters: your data.

Understanding the st.plotly_chart Deprecation Warning

The core of the issue lies in how Streamlit handles keyword arguments (kwargs) passed to st.plotly_chart. Recently, there have been some changes to how Streamlit manages these arguments, aiming for better clarity and to prevent potential conflicts or confusion. Specifically, the introduction of the config argument is meant to be the dedicated place for passing Plotly-specific configuration options. However, as observed, when you use arguments like width="content" or height="content", Streamlit might still trigger a deprecation warning related to kwargs, even if you're not explicitly passing any variable keyword arguments. This happens because the internal workings of st.plotly_chart might interpret these specific dimension arguments in a way that still flags them under the broader "kwargs" deprecation umbrella. The warning message itself, "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 bit of a catch-all. While it's designed to steer users towards the config argument for more complex Plotly settings, it inadvertently catches straightforward use cases like setting chart dimensions.

This situation can be particularly frustrating because it feels like a regression. If a feature worked perfectly fine in a previous version without any warnings, and now it generates a warning when used according to the documentation, it can create uncertainty. The goal of Streamlit is to make app development smooth and intuitive, and these kinds of warnings, even if they don't break functionality, can disrupt the developer experience. It's a reminder that sometimes, the underlying implementation of a library can evolve in ways that might not perfectly align with every single documented parameter's direct usage, especially when those parameters are integrated into the library's core rendering process. The developers are actively working to refine these messages and ensure they are as helpful as possible, guiding users towards best practices without causing unnecessary alarm.

Why This Happens: A Deeper Look

Let's unpack why this seemingly innocuous use of width="content" is triggering a warning. Streamlit's st.plotly_chart function is designed to be a versatile tool for embedding interactive Plotly charts within your Streamlit applications. To achieve this, it takes a Plotly figure object and several optional arguments to control its appearance and behavior. Among these arguments are width and height, which allow you to specify the dimensions of the chart. When you set width="content", you're essentially telling Streamlit to automatically adjust the chart's width to fit the available content area. This is a very convenient feature, as it helps ensure your charts look good regardless of the screen size or layout of your app.

However, the way Streamlit processes these arguments has undergone some refinement. Previously, the use_container_width parameter was the primary way to achieve this responsive sizing. As the library evolved, use_container_width was deprecated in favor of the more general width and height arguments, which offer greater flexibility. The warning you're encountering stems from the fact that even when you use the width or height arguments, Streamlit's internal logic might still be checking for or processing other potential keyword arguments. The deprecation warning is primarily aimed at discouraging the use of arbitrary, undocumented keyword arguments that could be passed directly to Plotly's underlying rendering functions. These could potentially override default Streamlit behaviors or lead to unexpected results.

In the specific case of width="content", while it's a documented and intended use, the implementation might still pass through a mechanism that the warning system flags as a potential "variable keyword argument." It's a bit like a security system that, while designed to catch burglars, occasionally flags a legitimate resident under certain circumstances. The intention behind the warning is good: to encourage users to keep Plotly-specific configurations within the dedicated config argument, ensuring that Streamlit's own rendering logic remains predictable and robust. By channeling these settings through config, you gain finer control over Plotly's behavior without interfering with Streamlit's app management.

This is why it might feel like a regression. If you were previously using use_container_width and then switched to width="content", expecting a seamless transition, the warning can be a confusing roadblock. It highlights a transitional phase in the library's development where newer, more flexible parameters are being introduced, and the old ways of handling certain configurations are being phased out. The developers are aware of this and are working on ensuring that documented parameters, especially those directly related to layout and sizing like width="content", do not trigger these broad deprecation warnings. The aim is to make the transition as smooth as possible for all users.

Reproducible Example and Expected Behavior

To make this issue crystal clear, let's look at a concrete example. Imagine you're creating a simple barpolar chart in Streamlit. You've imported the necessary libraries, created your Plotly figure, and now you want to display it. According to the Streamlit documentation, to make your chart dynamically resize with its container, you should use the width argument.

Here's the code that demonstrates the problem:

import plotly.graph_objects as go
import streamlit as st

# Create a simple Plotly figure
fig = go.Figure()
fig.add_trace(go.Barpolar(r=[1], theta=[0], width=[120]))
fig.update_layout(width=500, height=360) # These are Plotly layout parameters

# Display the chart using st.plotly_chart with width="content"
st.plotly_chart(fig, width="content")

When you run this code in a Streamlit application, you'll notice that even though you are using the documented parameter width="content" and not passing any other unspecified keyword arguments, Streamlit will still issue a deprecation warning. The warning typically states something 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."

Now, let's talk about the expected behavior. Based on the Streamlit documentation and the intent behind the width and height arguments, when you set width="content", the st.plotly_chart function should simply render the Plotly chart with its width adjusted to fit the surrounding container. It should not generate a deprecation warning. The warning is intended for situations where users might be passing arbitrary, undocumented keyword arguments that could interfere with Streamlit's rendering or Plotly's internal settings. Using width="content" is a standard, documented way to control the chart's responsiveness, and therefore, it should be treated as a valid parameter without triggering a warning.

The current behavior, where this documented parameter leads to a deprecation warning, suggests a slight misalignment between the warning system's trigger and the intended use of specific layout parameters. The goal is to ensure that developers can confidently use the provided arguments for layout control without receiving unnecessary warnings. This would mean that the if kwargs: check, or whatever mechanism triggers the warning, needs to be refined to differentiate between truly arbitrary keyword arguments and documented layout parameters like width="content".

Essentially, we expect st.plotly_chart(fig, width="content") to just work, displaying a responsive chart, and remaining silent on the deprecation front. This is crucial for maintaining a clean and predictable development environment in Streamlit. The transition from older methods like use_container_width to the newer width and height parameters should be as seamless as possible, and that includes the absence of spurious warnings.

The Current Behavior Explained

The current behavior, as you've likely experienced, is that the code snippet provided above, which uses st.plotly_chart(fig, width="content"), results in an unexpected deprecation warning. This warning message, often pointing to the deprecation of variable keyword arguments and suggesting the use of the config argument, appears even though width="content" is a documented and intended parameter for controlling chart responsiveness.

This behavior arises from how Streamlit's internal code is structured to handle arguments passed to st.plotly_chart. The warning mechanism is designed to catch situations where users might pass a variety of unspecified keyword arguments. These could be intended for Plotly's internal configuration, but if passed directly to st.plotly_chart without going through the config argument, they might cause issues or be interpreted as unsupported. The if kwargs: block within Streamlit's plotting functions is a safeguard.

In the case of width="content", Streamlit's internal logic might be processing this argument in a way that still triggers this if kwargs: condition. It's not that width="content" is a variable keyword argument in the problematic sense, but rather that its passage through the function's argument handling pipeline inadvertently triggers the warning flag. This is a common challenge when refactoring codebases; a general warning meant for a broad category of misuse can sometimes catch legitimate, albeit specific, use cases.

The developers have introduced the config argument as the preferred way to pass Plotly-specific settings. This allows Streamlit to maintain better control over how charts are rendered within the app environment. However, for basic layout adjustments like fitting the container width, developers traditionally relied on parameters that are now being more strictly managed. The warning aims to guide users towards the config dictionary for any settings that truly belong to Plotly's configuration object, distinguishing them from Streamlit's own layout controls.

Because this behavior was not present in previous versions, it is considered a regression. Developers expect that documented parameters will function as described without generating warnings. The current situation creates a less-than-ideal developer experience, as it introduces noise into the console output and can lead to confusion about whether the code is actually correct or if there's a more significant issue.

The debug information provided (Streamlit version 1.50.0, Python 3.14.2, macOS 26.1, Chrome browser) helps pinpoint the environment where this occurs, confirming it's not an isolated incident but rather a behavior present in a specific version of Streamlit.

The Path Forward: Addressing the Regression

It's clear that the current behavior, where using a documented parameter like width="content" with st.plotly_chart triggers a deprecation warning, is not ideal. This is especially true since it's considered a regression from previous versions where this functionality worked without any warnings. The good news is that the Streamlit team is actively working on refining these aspects of the library to improve the developer experience.

Solutions and Best Practices

While the Streamlit team addresses the root cause of this warning, there are a couple of ways you can navigate this. The most straightforward approach, if you find the warning particularly bothersome, is to suppress it. However, this should be done with caution, as you don't want to accidentally hide genuine issues. A more recommended approach is to ensure you are using the parameters as intended and to stay updated with Streamlit releases, as such issues are often resolved in subsequent updates.

For now, if you absolutely need to avoid the warning and are comfortable with the potential for future changes, you might consider how the config argument could be used, although this is generally more complex than needed for simple width adjustments. The primary goal is for the width and height arguments to work seamlessly. The development team is aware of this and will likely adjust the warning logic to exclude documented layout parameters like width="content".

Keeping Up-to-Date

Staying updated with the latest Streamlit releases is key. Deprecation warnings and regressions like this are often identified and fixed relatively quickly. By regularly updating your Streamlit installation (pip install --upgrade streamlit), you ensure that you're benefiting from the latest improvements and bug fixes. The Streamlit community and development team are responsive, and issues reported through channels like GitHub are taken seriously.

Ultimately, the fix will likely involve a minor adjustment within Streamlit's st.plotly_chart function to correctly differentiate between arbitrary keyword arguments and the explicitly documented width and height parameters when they are set to values like "content". This will restore the expected behavior: responsive charts without unnecessary warnings.

We encourage you to keep an eye on the official Streamlit documentation for any updates or changes regarding st.plotly_chart and its parameters. Understanding how these components evolve will help you build more robust and efficient Streamlit applications. For more in-depth discussions on Streamlit features and potential issues, the Streamlit Community Cloud forum is an excellent resource to connect with other developers and find solutions.