Fix Plotly Chart Width Warning In Streamlit

In the dynamic world of data visualization, developers often rely on powerful libraries to bring their insights to life. Streamlit has emerged as a favorite for its simplicity and speed in building interactive web applications. When it comes to integrating visualizations, the plotly_chart function in Streamlit is a go-to. However, users have recently encountered a rather perplexing deprecation warning when using the width="content" argument, even when they aren't explicitly passing any variable keyword arguments. This article aims to demystify this issue, explain why it's happening, and guide you toward a smooth resolution.

The Unexpected kwargs Warning: What's Going On?

When you're using st.plotly_chart and specify the width="content" (or height="content") parameter, you might notice a deprecation warning popping up. This warning 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 can be quite confusing because you're not trying to pass any extra, undefined keyword arguments (kwargs). You're simply using documented parameters like width to control the layout of your Plotly charts within your Streamlit app. This behavior suggests an internal handling of arguments within Streamlit that's triggering this warning, even when the user's intent is straightforward and aligned with the documented API.

Let's break down the scenario with a concrete example. Imagine you have a simple Streamlit app that displays a Plotly chart. You've created a plotly.graph_objects figure, perhaps a Barpolar chart, and you want it to dynamically adjust its width based on its content. The documentation suggests using width="content" for this purpose. So, your code might look something like this:

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")

When you run this code, Streamlit renders the chart as expected, but a warning message appears in your console or Streamlit's UI. This warning message, specifically about deprecated kwargs, is unexpected because you haven't used any **kwargs in your call to st.plotly_chart. You've only used fig (the Plotly figure object) and width="content", which are both explicitly defined parameters.

The core of the problem lies in how Streamlit's st.plotly_chart function handles arguments internally. It seems that when you pass width="content", Streamlit might be processing this argument in a way that its internal argument parsing interprets it as a variable keyword argument, thus triggering the deprecation warning related to kwargs. This is likely an unintended side effect of the internal implementation rather than a direct misuse of kwargs by the end-user. The warning's intent is to steer users away from passing arbitrary Plotly layout options directly as keyword arguments to st.plotly_chart, suggesting the config parameter as the correct place for such customizations. However, width and height are parameters of st.plotly_chart itself, not directly Plotly layout options passed through kwargs.

This issue can be particularly frustrating because it might lead developers to believe they are doing something wrong or that their code is about to break, even when they are following the documented usage. It's a signal that the library's internal mechanisms aren't perfectly aligned with the user-facing documentation for this specific scenario.

Why is this Happening? A Deeper Look

The plotly_chart deprecation warning, specifically concerning kwargs, arises from changes within Streamlit's argument handling for its plotting functions. Previously, users might have passed various Plotly-specific arguments directly as keyword arguments to st.plotly_chart. The Streamlit developers decided to consolidate these into a dedicated config argument to make the API cleaner and more predictable. This is a good practice for library maintenance, ensuring that future updates to Plotly don't break Streamlit's plotting interface unexpectedly.

The warning message is triggered by a check within the st.plotly_chart function: if kwargs:. This condition is designed to catch any keyword arguments that are not explicitly defined and handled by the function itself. The intention is to guide users to use the config dictionary for any Plotly-specific settings that should be passed to the underlying Plotly figure. For example, if you wanted to set Plotly's scrollZoom option, you would do it like this:

st.plotly_chart(fig, config={'scrollZoom': True})

However, the width and height parameters of st.plotly_chart are not Plotly layout options in the same way. They are Streamlit-specific arguments that control how the chart is rendered within the Streamlit app's layout. When you pass width="content", Streamlit's internal argument processing might be treating this value in a way that bypasses the explicit width parameter handling and inadvertently lands in the kwargs bucket before the check. This means the if kwargs: condition evaluates to true, even though kwargs might only contain width="content" which is a valid and intended argument for st.plotly_chart itself.

This suggests a slight mismatch between Streamlit's argument parsing logic and the intended use of parameters like width and height when set to special values like "content". The kwargs check is perhaps too broad or is being executed at a point where arguments like width haven't yet been fully processed as dedicated parameters.

Furthermore, the fact that this is reported as a regression indicates that in previous versions of Streamlit, this specific usage did not trigger the warning. This implies that the internal logic for handling width and height parameters, or the way kwargs are collected and checked, has changed in a way that inadvertently impacts this specific use case. The update might have been intended to improve argument handling generally, but it created an edge case.

Understanding this internal mechanism helps explain why the warning appears. It's not necessarily that you're passing arbitrary kwargs, but rather that the way you're passing a specific, documented parameter is being misinterpreted by Streamlit's internal checks.

Expected vs. Current Behavior: What Should Happen?

The expected behavior when using st.plotly_chart with specific arguments like width="content" is that the function should operate smoothly without issuing deprecation warnings, especially when those arguments are part of the documented API for controlling layout. The documentation clearly indicates that width and height are parameters that can be passed to st.plotly_chart to influence the displayed size of the chart. When you set width="content", the expectation is that Streamlit will attempt to size the chart based on its intrinsic content, providing a responsive layout. Similarly, height="content" would aim for content-based height.

This contrasts with the current behavior, where using width="content" (or height="content") triggers a deprecation warning about kwargs. The warning message itself guides users to use the config argument for Plotly configuration options. However, width and height are Streamlit-specific parameters for controlling the display of the chart within the app, not necessarily Plotly's internal layout configurations. Therefore, expecting a warning when using these parameters is counterintuitive.

To elaborate, the deprecation warning was introduced to discourage passing Plotly's layout attributes directly. For instance, passing xaxis_title='My Title' directly to st.plotly_chart would be incorrect and should ideally be handled via the config argument or by updating the Plotly figure directly (fig.update_layout(xaxis_title='My Title')). The warning is a mechanism to enforce this best practice. However, width="content" is a direct parameter of st.plotly_chart itself, meant to control the Streamlit component's rendering. It's not an arbitrary Plotly keyword.

The current behavior, therefore, is that the warning appears erroneously. This happens because Streamlit's internal code, when processing width="content", might be passing it through a pipeline that flags it as an unhandled kwargs, leading to the warning. The code snippet provided in the issue (if kwargs: show_deprecation_warning(...)) highlights this exact mechanism.

Essentially, the expected behavior is a seamless integration where documented parameters function as intended without generating false alarms. The current behavior introduces noise into the development process, potentially confusing developers about the correct way to use the API or leading them to ignore genuine warnings due to the presence of this false positive.

Resolving the plotly_chart Deprecation Warning

Dealing with the plotly_chart kwargs deprecation warning when using width="content" requires understanding the root cause and applying the correct Streamlit practices. Since this warning is a result of how Streamlit internally processes arguments, and specifically how it flags potential kwargs, the most effective solution is often to ensure that arguments intended for the st.plotly_chart function itself are handled appropriately, and any Plotly-specific configurations are passed via the config parameter.

In the case where width="content" or height="content" is causing the warning, and given that this is documented behavior for st.plotly_chart, the ideal resolution would be for the Streamlit library itself to adjust its internal argument parsing. This would mean that width and height parameters, when explicitly recognized by st.plotly_chart, would not be caught by the general kwargs deprecation check. However, as a user, you might need a workaround if an immediate fix from the library developers isn't available or if you need to deploy your application now.

One approach is to explicitly pass width and height as numerical values or None, and let Streamlit manage the layout. For instance, instead of width="content", you might try setting it to None or a specific pixel value if "content" isn't strictly necessary for your use case. However, this defeats the purpose of responsive sizing.

A more direct workaround, and one that aligns with the spirit of the deprecation warning (which advises using config for Plotly options), is to avoid passing width and height directly as arguments to st.plotly_chart if they trigger the warning. Instead, you can configure the figure's layout before passing it to st.plotly_chart. Plotly figures have a layout attribute that can be updated.

Here's how you could potentially adapt your code:

import plotly.graph_objects as go
import streamlit as st

fig = go.Figure()
fig.add_trace(go.Barpolar(r=[1], theta=[0], width=[120]))

# Instead of fig.update_layout(width=500, height=360) and st.plotly_chart(fig, width="content")
# Update the figure's layout directly for sizing hints, though this may not perfectly mimic 'content' width
# For true 'content' width behavior, relying on Streamlit's direct parameter is intended.

# If 'width="content"' is the trigger, and you don't want the warning, consider alternatives:
# 1. Remove width="content" and let Streamlit's default sizing handle it.
# 2. Set a fixed width if possible: st.plotly_chart(fig, width=600) 
# 3. If 'content' is critical and the warning persists, it's best to report this as a bug to Streamlit,
#    as it seems like an edge case in their argument handling.

# Let's demonstrate by *not* using width="content" and see if the warning disappears.
# If the warning is specifically tied to 'width="content"', and you NEED that behavior,
# the best immediate action is to acknowledge it as a known issue and await a library fix.

# For demonstration, we'll omit the problematic argument:
# st.plotly_chart(fig)

# If you *must* control size and avoid the warning, you might have to use fixed sizes
# or accept the warning as a known, non-breaking issue for now.

# The core issue is that st.plotly_chart(fig, width="content") itself is triggering the warning,
# suggesting an internal parsing issue.

# A workaround could be to use the config parameter for *other* Plotly settings,
# and hope that the width handling is somehow improved or isolated.

# Example without the problematic argument:
st.plotly_chart(fig) # This should not produce the kwargs warning.

# If you need to control the width and avoid the warning, you might need to look into
# Streamlit's layout options or use fixed pixel values.

# Let's assume the warning is indeed tied to `width="content"` specifically.
# The official recommendation in such cases is often to:
# 1. Check Streamlit's GitHub issues for similar reports.
# 2. If not found, file a new issue with a reproducible example.
# 3. In the meantime, accept the warning if it doesn't break functionality, or use workarounds
#    like fixed sizing if feasible.

The most robust solution is to report this as a bug to the Streamlit maintainers. Providing a clear, reproducible code example, as done in the original issue, is crucial. This allows the Streamlit team to investigate the internal argument handling and release a fix in a future version. Until then, if the warning is non-critical to your application's functionality, you might choose to ignore it. If it's disruptive, consider using fixed pixel dimensions for width and height if that meets your design requirements.

Conclusion: Navigating Streamlit's Plotting Features

While Streamlit's plotly_chart function offers a fantastic way to embed interactive Plotly visualizations into your applications, encountering unexpected deprecation warnings can be a hiccup in the development process. The specific warning related to kwargs when using width="content" is a prime example of how internal library changes can sometimes lead to user-facing confusion. It's important to remember that the warning's intent is generally to guide users towards a cleaner API, encouraging the use of the config parameter for Plotly-specific settings rather than passing them directly as keyword arguments.

However, when documented parameters like width and height themselves trigger this warning, it indicates a potential edge case in Streamlit's argument parsing. The good news is that this is often a non-breaking issue, meaning your chart will likely still render correctly. The primary impact is the appearance of the warning, which can be distracting and might lead to concerns about future compatibility.

The best course of action when encountering such issues is twofold: first, try to understand if there's a misunderstanding of the API or a simple workaround; second, if the behavior seems unintended or incorrect based on the documentation, contribute to the library's improvement by reporting it.

For this specific plotly_chart width="content" warning, the developers of Streamlit are the best equipped to address it by refining their internal argument handling. In the meantime, developers might need to accept the warning, use fixed dimensions if appropriate, or stay updated with Streamlit's release notes for potential fixes. This proactive engagement with library issues ensures that tools like Streamlit continue to evolve and become more robust for everyone.

For more in-depth information on Streamlit's features and best practices, you can refer to the official Streamlit Documentation. Additionally, for deeper insights into Plotly's capabilities and customization options, the Plotly Documentation is an invaluable resource.