Streamlit Plotly Chart Width Argument Warning

by Alex Johnson 46 views

Hey there, fellow Streamlit enthusiasts! Today, we're diving into a rather peculiar issue that some of you might have encountered when working with st.plotly_chart and its width parameter. Specifically, we're talking about a deprecation warning that pops up even when you're not explicitly using variable keyword arguments, but rather sticking to the documented parameters like width='content'. This can be a bit confusing, right? Let's unravel this together and figure out what's going on and how to navigate it.

Understanding the plotly_chart Deprecation Warning

So, you're building a beautiful interactive dashboard with Streamlit, and you're using st.plotly_chart to display your amazing Plotly visualizations. You decide to dynamically adjust the width of your chart to fill its container, which is a pretty common and useful feature. You set width='content', as the documentation suggests. Then, bam! a deprecation warning appears: "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, as many have noticed, can be quite jarring, especially when you feel like you haven't done anything wrong. You're not passing any extra, uncalled-for keyword arguments; you're just using the width parameter as intended. This leads to a bit of a head-scratcher, and it's precisely the kind of puzzle we're here to solve. We want to ensure that when you use Streamlit, your development experience is as smooth and intuitive as possible, free from unexpected warnings that might lead you down the wrong path. This warning, while intended to guide users towards better practices for future compatibility, seems to be a bit too eager in this particular scenario, flagging a correct usage as if it were an oversight. It's a subtle but important distinction that can impact the perceived stability and polish of your applications. We'll explore the exact mechanism behind this warning and discuss why it's appearing in this context, even when your code seems perfectly fine. Understanding the root cause is the first step towards a robust solution and a more predictable Streamlit experience.

Why is This Warning Appearing?

The core of the issue seems to stem from how Streamlit handles keyword arguments (kwargs) internally. In a recent update, Streamlit introduced changes to deprecate the direct use of variable keyword arguments for st.plotly_chart. The intention behind this change is to streamline the way Plotly configurations are passed, encouraging the use of the config argument for more explicit control. However, it appears that the warning mechanism might be a bit too sensitive. When you pass width='content' (or height='content'), this parameter is processed by Streamlit's internal logic. It seems that even though width is a documented and supported parameter for controlling the chart's display, the underlying code that checks for kwargs is being triggered. This is because, from the perspective of the warning's trigger, any argument passed to st.plotly_chart that isn't explicitly handled before the kwargs check might be flagged. The width parameter, in this specific implementation, is likely being interpreted as part of these kwargs by the warning logic, leading to the deprecation message. It's like a security system that's a little too sensitive, setting off the alarm even for authorized visitors. The developers' goal was to ensure that users don't pass arbitrary Plotly-specific kwargs directly, which could become outdated or conflict with future Streamlit updates. Instead, they want these Plotly configurations to be nested within the config dictionary. However, the current implementation of the warning check seems to be catching legitimate, Streamlit-defined parameters like width and height as if they were those arbitrary kwargs. This is a classic case of an overzealous automation that needs a bit of fine-tuning. We'll delve into the code snippet that generates this warning to illustrate this point more clearly. It's a detail that, while seemingly minor, is crucial for developers who strive for clean, warning-free codebases. This behavior might also be considered a regression, as it worked as expected in previous versions without triggering this warning, adding to the confusion and frustration.

Reproducible Code Example and Expected Behavior

Let's walk through a simple example to make this crystal clear. Imagine you have the following Python 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]))
fig.update_layout(width=500, height=360)

st.plotly_chart(fig, width="content")

Here, we create a basic Plotly figure and then display it using st.plotly_chart. We've explicitly set the width parameter to 'content', intending for the chart to take up the available horizontal space within its container. Now, what should happen? According to the Streamlit documentation and general expectations for stable libraries, this should just work. The st.plotly_chart function should render the Plotly figure, and the width='content' should be correctly interpreted and applied. No warnings should be issued because width is a recognized and documented parameter for controlling the chart's dimensions. The expected behavior is a clean execution, displaying your chart beautifully without any unnecessary alerts. You should see your Plotly chart rendered within the Streamlit app, adapting its width as intended.

The Current Behavior: An Unwanted Warning

However, as many of you have experienced, the current behavior deviates from this expectation. When you run the code snippet above, instead of a silent execution, you'll likely see a deprecation warning printed in your Streamlit app's console or output. This warning typically looks something like this:

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 appears even though width='content' is a documented parameter and not a stray, undefined keyword argument. The issue arises because of the internal logic within Streamlit's st.plotly_chart function. A specific block of code is designed to detect if any kwargs are being passed. This check is likely implemented as:

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."
    )
# ... rest of the function that might process other arguments like 'width'

Because width='content' is passed as a keyword argument (even though it's a documented one), it gets caught by this if kwargs: check before Streamlit's internal processing potentially separates it into its own handling logic. This leads to the warning being displayed erroneously. The developers' intention was to warn against passing arbitrary Plotly kwargs that should instead be in the config dictionary. But in this case, a valid Streamlit-specific argument is being flagged. This is a significant point because it can deter users from using perfectly valid features due to the fear of accumulating warnings or due to the perceived instability it suggests. It's a bug that needs to be addressed to ensure a clear and accurate user experience.

Is This a Regression?

Yes, this behavior is indeed a regression. This means that in previous versions of Streamlit, using st.plotly_chart with parameters like width='content' or height='content' did not trigger this deprecation warning. Users could leverage these display-controlling arguments without any issue. The fact that it worked correctly before but now raises a warning indicates a change in the library's internal handling or warning mechanisms. This regression is particularly frustrating because it affects a common use case and can make developers question whether they are using the library correctly. When a feature that was once stable and predictable starts behaving differently, it often signals a need to re-evaluate the code, only to find that the code itself hasn't changed, but the library's behavior has. This regression highlights the importance of thorough testing for updates, especially when changes involve internal argument handling and warning systems. It's a clear indicator that the recent modifications, while perhaps aimed at improving future compatibility, have inadvertently broken a functional aspect of the current API. Addressing this regression is crucial for maintaining developer trust and ensuring a seamless experience when upgrading Streamlit versions.

Debugging Information and Potential Solutions

To further pinpoint the issue, let's consider the provided debugging information:

  • Streamlit version: 1.50.0
  • Python version: 3.14.2
  • Operating System: MacOs 26.1
  • Browser: Chrome

This information confirms that the issue is present on a specific version of Streamlit (1.50.0) and is reproducible across different environments. The fact that it's marked as a regression further solidifies that this is an unintended change in behavior.

What's Happening Under the Hood?

As mentioned, the warning is triggered by this conditional check:

if kwargs:
    show_deprecation_warning(...)

The kwargs variable in Python collects any keyword arguments passed to a function that are not explicitly defined as parameters. In the context of st.plotly_chart(fig, width='content'), the width='content' is indeed being passed as a keyword argument. The issue is that the warning logic is too broad; it doesn't differentiate between valid, documented Streamlit parameters (like width, height, use_container_width) and arbitrary, unhandled Plotly kwargs. Ideally, Streamlit's st.plotly_chart function should first process its own specific arguments (width, height, use_container_width, config, etc.) and only then check if any remaining kwargs exist before issuing the deprecation warning.

Potential Fixes and Workarounds

For users encountering this warning, here are a few approaches:

  1. Use use_container_width=True (if applicable): If your goal is simply to make the chart fill the container width, st.plotly_chart(fig, use_container_width=True) is the more idiomatic and potentially less problematic way to achieve this. This parameter is specifically designed for this purpose and might bypass the kwargs warning trigger.
  2. Pass width within config: While the documentation mentions width as a direct parameter, Plotly itself often uses a config dictionary for display options. You might be able to achieve a similar effect by passing config={'width': 'content'} or by using Plotly's layout.width if st.plotly_chart forwards such arguments correctly. However, this might not directly correspond to Streamlit's container-aware width.
  3. Ignore the warning (with caution): If you are confident that your code is correct and the warning is purely cosmetic due to this specific regression, you could choose to ignore it. However, this is generally not recommended as it might mask other potential issues or lead to unexpected behavior in future updates.
  4. Report the bug: The most constructive approach is to report this issue to the Streamlit developers. By providing a clear, reproducible example, you help them identify and fix the bug in a future release. This issue has already been reported, which is a good step.

Conclusion: Moving Forward

While the plotly_chart kwargs deprecation warning can be a bit of a red herring when using documented parameters like width='content', it's important to understand its origin. It stems from an overly broad check for keyword arguments in Streamlit's internal handling. The good news is that this is recognized as a regression, and the Streamlit team is likely working on a fix. In the meantime, using use_container_width=True is often the best alternative if your goal is to make the chart responsive to its container. Always refer to the official Streamlit documentation for the most up-to-date information on parameters and best practices.

For further insights into Streamlit and Plotly integration, you might find these resources helpful: