Streamlit: Fix Plotly_chart Kwargs Deprecation Warning

If you've been working with Streamlit and Plotly, you might have encountered a rather persistent warning lately: the plotly_chart kwargs deprecation warning. This can be a bit confusing, especially when you're just trying to set the size of your charts using documented parameters like width="content". It seems like you're following all the rules, but still, this warning pops up, making you wonder if you're doing something wrong. Don't worry, you're not alone, and we're here to demystify this. This warning, while seemingly minor, points to an underlying change in how Streamlit handles arguments passed to st.plotly_chart, particularly concerning variable keyword arguments (kwargs). The intention behind this change is to streamline the process and make it more robust, but it can lead to unexpected warnings for users who aren't explicitly passing arbitrary keyword arguments. Let's dive into what's happening and how you can navigate it smoothly.

Understanding the plotly_chart Kwargs Deprecation Warning

The core of the issue lies in how the st.plotly_chart function now processes arguments. Previously, Streamlit was more lenient with accepting various keyword arguments, which could sometimes lead to unexpected behavior or ambiguity. To address this, the developers have introduced a stricter approach, aiming to guide users towards more explicit and supported ways of configuring their charts. The deprecation warning specifically targets the use of variable keyword arguments (often denoted as **kwargs in Python functions). This means that if you pass any argument to st.plotly_chart that isn't a specifically defined parameter in the function's signature, you'll likely see this warning. This is intended to prevent the accidental passing of arguments that might be ignored or misinterpreted, ensuring that your chart configurations are clear and intentional. The warning message itself suggests using the config argument for specifying Plotly configuration options, which is the recommended way forward. For instance, when you set width="content" or height="auto" (or similar directives), Streamlit interprets these as parameters for controlling the chart's dimensions. However, under the hood, the way these are handled might trigger the kwargs warning if the internal implementation relies on passing them through a kwargs mechanism that the new Streamlit version is scrutinizing more closely. It's not necessarily that you are incorrectly using kwargs, but rather that the function's internal workings might be contributing to this warning. The goal is to ensure that only explicitly documented parameters are used, making the code more predictable and maintainable. This deprecation is a signal that the API is evolving, and it's a good practice to adapt to these changes to avoid potential issues in future updates. By understanding that this warning is primarily about how arguments are passed internally and encouraging explicit usage, you can better manage your Streamlit applications and ensure they remain compatible with future versions.

Why the Warning Appears Even Without Explicit **kwargs

This is perhaps the most perplexing part for many users: you're not explicitly using **kwargs in your code, yet the warning persists. The reason behind this is that the st.plotly_chart function, like many Python functions, might use **kwargs internally to pass along arguments to the underlying Plotly library or to handle configuration options that aren't explicitly named in its own function signature. When you provide arguments like width="content" or height=360, these are valid ways to control your Plotly chart's appearance. However, the Streamlit framework might be passing these arguments through its own internal kwargs handling before they reach the Plotly chart object. The deprecation warning is triggered because the new Streamlit version is designed to flag any use of variable keyword arguments, whether they originate from the user's direct input or from the framework's internal processing. This is a proactive measure to ensure that developers are aware of how arguments are being managed and to encourage the use of specific, documented configuration methods. The warning message, "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 clear hint. While width and height are not variable keyword arguments in the sense of being arbitrary, their internal handling within Streamlit might be passing through a mechanism that the deprecation targets. It's a subtle distinction, but important to understand. The developers are essentially saying, "We want to make sure you're using the intended channels for configuration." In this case, for chart dimensions and other Plotly-specific settings, the config dictionary is the designated channel. So, even if you're using a seemingly innocent parameter like width="content", the warning arises because Streamlit's internal machinery might be employing kwargs to manage these parameters, and this is now being flagged for future removal. The expectation is that users will progressively shift towards using the config dictionary for all Plotly-related configurations, including dimensions, which offers a more unified and explicit control over the chart's behavior and appearance within the Streamlit environment.

Reproducible Code Example and Expected Behavior

Let's look at a practical example to illustrate the situation. Consider this Python code using Streamlit and Plotly:

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")

In this snippet, we create a simple Plotly figure and then display it using st.plotly_chart. We've explicitly set width="content" as an argument to st.plotly_chart. According to the Streamlit documentation, parameters like width and height are the correct way to influence the dimensions of the displayed chart. Therefore, the expected behavior is that this code should run without any deprecation warnings. The width="content" argument should correctly instruct Streamlit to size the chart based on its container, and no warning regarding kwargs should be issued because we are using documented parameters. The user is not passing arbitrary or undefined keyword arguments. However, as the issue report indicates, the current behavior is that running this code triggers the 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 is precisely the crux of the problem – a documented and seemingly correct usage is resulting in a warning that suggests a different approach. The warning implies that width="content" is being treated as a variable keyword argument, which is not the intended interpretation from the user's perspective. The underlying issue is that the internal implementation of st.plotly_chart might be passing these dimension arguments through a kwargs mechanism, which is now being flagged. The ideal scenario is that Streamlit distinguishes between its own documented arguments (like width, height, use_container_width) and arbitrary **kwargs, and that using documented arguments does not trigger warnings related to internal kwargs usage. This discrepancy highlights a need for refinement in how Streamlit handles and signals deprecations, ensuring that user-facing parameters are clearly demarcated from internal implementation details that might trigger warnings.

The Path Forward: Adapting to the Changes

This deprecation warning, while initially confusing, is a sign of Streamlit's continuous effort to improve its API and provide a more structured development experience. The key takeaway is to adapt to the recommended practices to ensure your applications are future-proof. The warning explicitly suggests using the config argument to specify Plotly configuration options. This is where you should direct your attention. Instead of relying on direct arguments like width and height for st.plotly_chart when they might be internally processed via kwargs, you can pass these settings within the config dictionary. For example, if you want to ensure your Plotly chart takes up the full width of its container, you would use st.plotly_chart(fig, config={'responsive': True, 'autosize': True}) or similar configurations that Plotly itself recognizes. While width='content' might not have a direct one-to-one mapping within the config dictionary in the same way, the principle remains: consolidate your Plotly-specific configurations within the config parameter. You might need to consult the Plotly documentation for the specific keys and values that correspond to the behavior you're aiming for. For instance, use_container_width=True was a previous Streamlit parameter, and its functionality is often achieved through Plotly's own responsive settings. The core idea is to move away from passing dimension or Plotly-specific settings directly as top-level arguments to st.plotly_chart when those arguments are not explicitly part of Streamlit's core st.plotly_chart API (like fig, key, height, width, use_container_width). Instead, they should be nested within the config dictionary. This approach offers a more unified way to manage Plotly's extensive customization options. By embracing the config argument, you not only avoid the deprecation warning but also gain finer control over your Plotly charts, ensuring consistency and compatibility with future Streamlit and Plotly updates. It's an investment in the stability and maintainability of your data visualization projects.

Conclusion: Embracing Clarity in Streamlit Visualizations

Encountering deprecation warnings can be a hiccup in the development process, but they often serve as valuable guides toward better coding practices. The plotly_chart kwargs deprecation warning in Streamlit, particularly when using arguments like width="content", highlights a shift towards more explicit and organized configuration. While it might seem counterintuitive to receive a warning when using documented parameters, understanding that this relates to the internal handling of arguments clarifies the situation. By migrating your Plotly-specific configurations, including sizing and other visual adjustments, into the config dictionary argument of st.plotly_chart, you align with Streamlit's evolving API. This not only silences the warning but also enhances the robustness and maintainability of your Streamlit applications. As you continue to build interactive dashboards and visualizations, remember that embracing these changes leads to more stable and future-ready projects. Keep exploring the capabilities of Streamlit and Plotly, and don't hesitate to consult their respective documentation for the most up-to-date guidance.

For further information on Streamlit's components and best practices, you can always refer to the official Streamlit Documentation. And for deep dives into Plotly's extensive charting capabilities, the Plotly Documentation is an invaluable resource.