Streamlit: Fixes Plotly Chart Deprecation Warnings

If you're a Streamlit user who loves to visualize data with Plotly, you might have encountered a rather annoying deprecation warning recently. It pops up even when you're not doing anything out of the ordinary, specifically when using st.plotly_chart with arguments like width="content" or height. This isn't just a minor glitch; it's a deprecation warning that appears even when you're not explicitly passing variable keyword arguments, which can be confusing and clutter your app's output. Let's dive into why this is happening and how to get around it.

Understanding the st.plotly_chart Deprecation Warning

The core of the issue lies in how Streamlit handles keyword arguments (kwargs) passed to st.plotly_chart. Recently, there was a change to deprecate the use of variable keyword arguments for passing Plotly configuration options. Instead, users are encouraged to use the config argument for such settings. This is a good practice for keeping the API clean and predictable. However, the implementation of this change inadvertently caused a deprecation warning to trigger even when users were simply specifying width="content" or height. These are documented parameters, not variable keyword arguments, so seeing a warning related to kwargs here feels like a bug. This warning is misleading because it suggests you're misusing keyword arguments when you're actually using standard, documented parameters. It's a classic case of a good intention leading to an unexpected side effect. The intention was to steer users towards the config parameter for advanced Plotly settings, preventing potential conflicts or ambiguity with other arguments st.plotly_chart might accept. But in doing so, the warning check became a bit too broad, catching legitimate uses of width and height parameters. This can be particularly frustrating during development when you're trying to ensure your app is clean and warning-free. Imagine you've carefully structured your code, used the documented parameters correctly, and then a spurious warning appears. It forces you to investigate, potentially wasting valuable development time. The problem description highlights that this is indeed a regression, meaning it worked as expected in a previous version. This further emphasizes that it's not a user error but rather an issue with the recent Streamlit update. The provided code example clearly demonstrates the scenario: a simple Plotly figure is created, and then st.plotly_chart is called with width="content". According to the documentation, this should be a valid way to control the chart's width, making the deprecation warning unwarranted. The summary of the issue succinctly states the problem: "When using st.plotly_chart with width='content' (or height), users receive a deprecation warning about kwargs even when they are not explicitly passing any variable keyword arguments and are only using documented parameters." This perfectly captures the essence of the bug and its impact on developers trying to build clear and functional Streamlit applications. The goal is to have Streamlit provide feedback on actual issues, not on correct usage that happens to trigger an overly sensitive warning.

Reproducing the Issue: A Simple Code Example

To truly understand the problem, let's look at the reproducible code example provided. It’s a straightforward demonstration that highlights how the deprecation warning emerges unexpectedly. We start by importing the necessary libraries: plotly.graph_objects for creating the figure and streamlit for the web app framework.

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, a go.Figure is initialized, and a simple Barpolar trace is added. The figure’s layout is then set with specific width and height values (500 and 360, respectively). The crucial part is the final line: st.plotly_chart(fig, width="content"). Here, we're telling Streamlit to render the Plotly chart, and we're attempting to control its width by setting it to "content". This value is intended to make the chart adapt to the available width of its container, a very common and useful behavior. However, when you run this code in a Streamlit application (specifically, versions where this bug exists, like 1.50.0), you will see a 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 warning is perplexing because we haven't passed any arbitrary kwargs. The width="content" parameter is a documented argument for st.plotly_chart. Streamlit's internal logic, intended to catch the misuse of generic keyword arguments for Plotly configuration, is incorrectly flagging this standard parameter. This means that even when adhering to the documentation and using the intended parameters, developers are presented with a warning that suggests they are doing something wrong. The regression aspect is key here; this behavior was not present before, implying a recent change in Streamlit's internals has introduced this unintended consequence. The steps to reproduce are simple: run the code. The error isn't hidden behind complex configurations or obscure features; it's right there, visible with minimal setup. This makes it easy for the Streamlit team to identify and fix the issue, ensuring a smoother experience for all users.

The Expected vs. Current Behavior: A Discrepancy

Let's break down the discrepancy between what we expect and what's currently happening with st.plotly_chart. The expected behavior is clear and aligns with the documentation: when you use st.plotly_chart and specify parameters like width or height, these should be accepted and acted upon without any deprecation warnings, especially if they are documented parameters. The move from use_container_width to the more explicit width and height arguments was intended to provide better control and clarity. Therefore, using width="content" should simply instruct the chart to fill its container, and that should be the end of it. No warnings, no fuss. It’s about using the API as intended and documented.

The current behavior, however, tells a different story. As observed in the issue description and the reproducible code, a deprecation warning is issued: Variable keyword arguments for st.plotly_chart have been deprecated and will be removed in a future version. Use the config argument instead to specify Plotly configuration options. This warning is triggered specifically when width="content" (or height) is used. The problem stems from a check within Streamlit's code that looks for any kwargs being passed. The logic, implemented to guide users towards the config parameter for advanced Plotly settings, is too aggressive. It doesn't differentiate between actual, arbitrary kwargs that might be intended for Plotly's internal configuration and the documented width and height parameters that Streamlit itself exposes and manages. This leads to a situation where using standard, documented arguments results in a warning about deprecated keyword arguments. This is not just a minor inconvenience; it can lead developers to second-guess their implementation or spend time debugging a non-existent problem. It's a regression because, in earlier versions of Streamlit, this functionality worked seamlessly without the warning. The fix should ideally involve refining the check for kwargs so that it only flags truly variable keyword arguments intended for Plotly configuration, and not the specific, documented parameters like width and height that Streamlit handles directly. The goal is to ensure that warnings are informative and accurate, guiding users correctly without causing confusion or alarm when they are following best practices and documentation.

Why This Matters: Maintaining a Clean Development Environment

Encountering and having to address deprecation warnings, especially when they arise from using the software as intended, can be a significant drain on developer productivity. A clean console output is crucial for debugging and understanding the true state of an application. When spurious warnings flood the logs, it becomes much harder to spot genuine issues or warnings that require immediate attention. This specific warning, related to kwargs in st.plotly_chart, is particularly problematic because it misdirects developers. Instead of indicating a real problem with how Plotly configurations are being passed, it suggests a misuse of keyword arguments when, in fact, documented parameters like width='content' are being employed correctly. This can lead to unnecessary investigation, confusion, and a loss of confidence in the framework's stability and documentation.

Furthermore, the fact that this is identified as a regression means that a previously working feature has been broken by a recent update. This can be disruptive for projects that rely on specific Streamlit behaviors. Users expect that updates will either introduce new features or fix bugs, not break existing, well-documented functionality. The current behavior forces developers to either ignore the warning (which is bad practice) or implement workarounds that might not be ideal. The ideal solution is for Streamlit to correctly differentiate between true kwargs intended for Plotly's internal configuration and the explicit parameters managed by Streamlit itself, such as width and height. This refinement ensures that deprecation warnings are accurate, actionable, and serve their intended purpose: to guide developers toward best practices without introducing false alarms. A well-maintained and predictable API is fundamental to building robust applications, and addressing such issues promptly is key to fostering a positive developer experience. It allows developers to focus on building great features rather than deciphering confusing warnings.

The Path Forward: Ensuring Accurate Warnings

The resolution for this st.plotly_chart deprecation warning hinges on a more nuanced implementation within Streamlit's codebase. The warning is triggered by a check for the presence of kwargs when st.plotly_chart is called. The intention behind this check is to guide users toward the config parameter for passing Plotly-specific configurations, which is a sensible approach for maintaining API clarity. However, the current implementation is overly broad, flagging the use of documented parameters like width='content' as if they were arbitrary kwargs. The fix requires Streamlit to intelligently distinguish between these two scenarios. It needs to recognize when width or height are being used as explicit parameters, rather than being bundled into a generic kwargs dictionary that might contain other Plotly configurations. This could involve modifying the st.plotly_chart function to explicitly check for and handle width and height before evaluating the general kwargs. By doing so, Streamlit can ensure that the deprecation warning is reserved for instances where users are indeed passing variable keyword arguments that should be managed through the config parameter. This targeted approach ensures that the warning remains a valuable tool for guiding users toward best practices without causing confusion or flagging correct usage. It’s about making the warning system smarter and more precise. As a regression, this issue should be prioritized to restore the expected behavior for users who relied on setting chart dimensions directly. Ultimately, the goal is to maintain a development environment where warnings are informative and accurate, allowing developers to focus on building their applications without unnecessary distractions. For users looking for more information on Streamlit components and best practices, the official Streamlit Documentation is an invaluable resource.