Streamlit Plotly Chart: Width='content' Deprecation Warning Fix

In the dynamic world of web development and data visualization, staying updated with the latest features and best practices is key. When working with Streamlit, a popular Python library for creating interactive web applications, you might encounter a deprecation warning related to plotly_chart and its width argument, especially when setting it to "content". This warning can be a bit confusing, particularly if you're not explicitly passing variable keyword arguments (**kwargs). Let's dive into what this means and how to navigate it effectively.

The Nuance of st.plotly_chart and Keyword Arguments

Streamlit's st.plotly_chart function is a powerful tool for embedding interactive Plotly charts directly into your applications. It offers several customization options, including controlling the width and height of the displayed chart. Recently, there was a change in how Streamlit handles additional keyword arguments passed to this function. The core idea behind this change was to encourage more explicit control over Plotly configurations, steering users towards the config argument for Plotly-specific settings rather than relying on general keyword arguments that might be misinterpreted or cause conflicts. The deprecation warning aims to guide developers toward using the config parameter for Plotly configurations, which is a more robust and maintainable approach for managing the intricate settings of Plotly figures. This is particularly relevant when you want to control aspects like chart responsiveness, display modes, and other interactive features that are deeply tied to the Plotly.js library itself. By consolidating these settings within the config argument, Streamlit can ensure better compatibility and clarity in how these customizations are applied, preventing potential ambiguities that could arise from a more open-ended keyword argument system. It’s a move towards a more structured and predictable API, ensuring that as Streamlit and Plotly evolve, your applications remain stable and aligned with the latest best practices.

What Triggers the Warning?

The warning specifically pops up when you use st.plotly_chart with width="content" (or height="content"). This is interesting because, as noted in the issue report, the warning appears even when you're not explicitly passing any variable keyword arguments. It seems that the underlying mechanism that checks for kwargs might be triggered by the presence of the width or height arguments themselves, even though they are documented parameters. This can lead to a bit of confusion, as the warning suggests a deprecation of variable keyword arguments, which you might not be directly utilizing. The warning's text, "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," points to a broader change in how Streamlit handles Plotly-related arguments. While width and height are indeed parameters for st.plotly_chart, the internal implementation might be treating their dynamic setting (like "content") in a way that intersects with the kwargs handling. This is likely an unintended consequence of the refactoring, where a general check for kwargs is being performed, and arguments like width are being caught in that net. The goal is to ensure that users are aware of the preferred method for configuring Plotly charts, which is through the dedicated config parameter. This ensures that any Plotly-specific settings are correctly passed to the Plotly rendering engine without interfering with Streamlit's own argument processing. The behavior described is a classic example of how subtle implementation details can lead to unexpected user experiences, and it highlights the importance of thorough testing across various common use cases during library updates.

A Closer Look at the Code

The issue arises from a specific code snippet within Streamlit's plotly_chart function:

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 block of code is designed to issue a warning whenever kwargs is not empty. In the context of using st.plotly_chart(fig, width="content"), it appears that even though width="content" is a valid, documented parameter for controlling the chart's display, it's somehow contributing to the kwargs being non-empty from the perspective of this warning check. This is likely a side effect of how Streamlit processes arguments internally. It's important to distinguish between Streamlit's own arguments for st.plotly_chart (like fig, use_container_width, width, height) and Plotly's internal configuration options. The deprecation is aimed at the latter being passed through general kwargs. However, the current implementation seems to be misinterpreting the presence of a valid width or height argument as an instance of using undocumented kwargs. The intent behind the warning is to push users towards the config dictionary for Plotly-specific settings, such as `{