Resolving Streamlit `plotly_chart` Kwargs Deprecation Warning

When developing interactive data applications with Streamlit, integrating powerful visualization libraries like Plotly is a common and effective strategy. The st.plotly_chart function acts as a bridge, allowing your beautifully crafted Plotly figures to shine within your Streamlit apps. However, it's not uncommon to encounter occasional hiccups or warnings as these libraries evolve. One particular warning that has caught the attention of many developers recently is the kwargs deprecation warning when using st.plotly_chart, especially when trying to control chart dimensions with seemingly standard arguments like width="content". This can be a bit confusing, as you might think you're using documented parameters, yet Streamlit is telling you that you're passing deprecated keyword arguments. This article aims to demystify this specific plotly_chart kwargs deprecation warning, explain its root cause, and guide you through the best practices to resolve it, ensuring your Streamlit applications remain robust and future-proof. We'll dive into why this warning appears, what Streamlit intends with its API changes, and how you can confidently adjust your code to maintain a smooth development experience.

Deciphering the st.plotly_chart kwargs Deprecation Warning

If you've been working with Streamlit and Plotly, you've likely appreciated the simplicity and power of st.plotly_chart. It's a fantastic tool for embedding dynamic, interactive Plotly figures directly into your web applications, bringing your data to life with rich visualizations. From intricate scientific plots to straightforward business dashboards, plotly_chart handles it all, allowing users to zoom, pan, and interact with your data effortlessly. However, a recent development in Streamlit's API has led to a particular deprecation warning that can be a source of confusion: the dreaded message about kwargs being deprecated in st.plotly_chart. This warning typically states something along the lines of "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." What makes this especially perplexing for developers is that this warning can appear even when you're not explicitly passing arbitrary keyword arguments, but rather using documented parameters such as width="content" or height. It feels like you're following the rules, yet still getting flagged. Understanding deprecation warnings is crucial in software development. They aren't just annoying pop-ups; they are vital signals from the library maintainers, indicating that certain functionalities or ways of doing things will be changed or removed in future versions. Ignoring these warnings can lead to broken code down the line, requiring more significant refactoring. In Streamlit's case, this specific plotly_chart warning points towards a refinement in how plotly.js configuration options and figure sizing are managed within the Streamlit ecosystem. Streamlit is continuously evolving its API to offer a more consistent, efficient, and maintainable way to build data apps. This particular deprecation is part of that journey, pushing developers towards clearer and more explicit methods for configuring their Plotly charts.

The Core Issue: width="content" and Unexpected kwargs

Let's get to the heart of the matter: why does a seemingly innocent parameter like width="content" trigger a kwargs deprecation warning in st.plotly_chart? The problem often lies in how Streamlit's internal logic interprets arguments and how it transitioned from older API patterns to newer ones. Consider the reproducible code example that often leads to this issue:

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") # This line triggers the warning

In older versions of Streamlit, there was a parameter use_container_width that allowed Plotly charts to automatically expand to the width of their container. This was a very convenient feature for creating responsive layouts. As Streamlit's API matured, this functionality was streamlined, and the width argument was introduced to replace use_container_width in certain contexts, with width="content" being its semantic equivalent. However, in specific Streamlit versions, particularly around 1.50.0 as noted in the issue, the internal mechanism for handling arguments to st.plotly_chart developed a regression. The core of the problem, as highlighted in the provided debug information, is a piece of code that looks something like this:

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 if kwargs: check is designed to catch any unexpected keyword arguments that are not explicitly recognized by st.plotly_chart's signature and are therefore considered