Streamlit: Fix Plotly_chart Kwargs Deprecation Warning

by Alex Johnson 55 views

When you're building interactive dashboards and data visualizations with Streamlit, you often rely on tools like Plotly to create stunning charts. You might have encountered a peculiar warning message recently: "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 can be a bit confusing, especially when you're not explicitly passing any variable keyword arguments, and are instead using documented parameters like width='content'. Let's dive into why this happens and how to address it.

The Root of the Warning: How kwargs Work

In Python, **kwargs (keyword arguments) is a special syntax that allows a function to accept an arbitrary number of keyword arguments. These arguments are then collected into a dictionary. For instance, if you have a function defined as def my_function(**kwargs):, and you call it like my_function(name='Alice', age=30), kwargs inside the function will be {'name': 'Alice', 'age': 30}. This is incredibly useful for creating flexible functions that can handle various inputs without needing to define every single parameter explicitly.

Streamlit's st.plotly_chart function, like many others, has historically used **kwargs to pass along configuration options or arguments to the underlying Plotly library. This was a convenient way to allow users to pass almost any Plotly-specific setting directly to the Streamlit function. However, as libraries evolve and best practices change, relying on a catch-all **kwargs can sometimes lead to ambiguity or make it harder for developers to maintain and update the code. It can be unclear which arguments are expected and which are just being passed through.

The core of the issue is that Streamlit's st.plotly_chart function checks if there are any kwargs present after it has processed its own specific arguments. If there are, it triggers the deprecation warning. The intention behind this change is to encourage more explicit and organized configuration. Instead of passing a free-form set of keyword arguments, Streamlit wants you to use a dedicated config dictionary for Plotly-specific settings. This makes the code more readable and less prone to errors.

Why You See the Warning Even Without Explicit kwargs

This is where the confusion often arises. You might be using st.plotly_chart(fig, width='content'), and you're thinking, "I'm not using any **kwargs here!" That's technically true from your perspective. You're using a documented parameter, width. However, Streamlit's internal implementation might be processing these arguments in a way that still results in kwargs being populated. Specifically, when you pass width='content', this argument is not directly handled by st.plotly_chart's own defined parameters. Instead, it's likely being treated as a keyword argument that should be passed along to Plotly's rendering mechanism.

To illustrate this, consider the simplified internal logic of st.plotly_chart:

def plotly_chart(figure, **kwargs):
    # Streamlit processes its own arguments first, e.g., use_container_width
    # Let's say 'width' is NOT one of Streamlit's direct arguments here

    # If any arguments remain in kwargs after Streamlit's processing...
    if kwargs:
        # Trigger the deprecation warning
        show_deprecation_warning(
            "Variable keyword arguments for st.plotly_chart have been "
            "deprecated... Use the config argument instead..."
        )
        # ...and potentially pass remaining kwargs to Plotly

    # ... rest of the plotting logic

In this scenario, when you call st.plotly_chart(fig, width='content'), the width='content' part ends up in the kwargs dictionary. Since kwargs is not empty, the deprecation warning is triggered, even though width is a recognized parameter for controlling the chart's display. This is a common source of frustration because the warning seems to appear out of nowhere, implying that the user is doing something wrong when they are simply trying to use a documented feature.

The Expected Behavior vs. Current Behavior

The expected behavior when migrating from older versions or using the latest documentation is that parameters like width and height should be handled gracefully without raising deprecation warnings. The documentation for st.plotly_chart often suggests using width or height (or use_container_width in older versions) to control the display size of the Plotly figure within your Streamlit app. When you use these parameters as intended, you shouldn't be penalized with a warning that suggests you're misusing keyword arguments.

However, the current behavior, as observed in Streamlit version 1.50.0 and potentially others, is that passing width='content' (or potentially height='content') does indeed trigger the kwargs deprecation warning. This happens because, internally, the width parameter is being captured by the **kwargs mechanism before Streamlit can explicitly handle it as a display-sizing argument. The warning is designed to catch any unexpected keyword arguments, and unfortunately, it's catching documented ones in this specific context.

This indicates a slight mismatch between Streamlit's internal argument processing for st.plotly_chart and how it communicates deprecation. The warning's logic, which simply checks for the existence of kwargs, is too broad for this specific use case where width and height are intended to be passed through or handled directly.

Reproducible Code Example

To make this issue clear and reproducible, let's look at the provided 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")

When you run this code in a Streamlit environment with the affected version, you will see the Plotly chart rendered correctly, but accompanied by the deprecation warning. The chart itself functions as expected, but the warning message can be a source of concern for developers, making them believe they've made a mistake or that their code is less robust than it is.

Is This a Regression?

Yes, this is a regression. In previous versions of Streamlit, using parameters like width='content' with st.plotly_chart did not trigger this kwargs deprecation warning. The change in behavior suggests that an update to Streamlit's argument handling or Plotly integration has inadvertently caused this issue. Regressions are particularly problematic as they can break existing applications and introduce confusion for users who relied on previous, stable functionality.

Debug Information

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

This debug information is crucial for developers to pinpoint the exact environment and versions where the issue occurs, aiding in the process of identifying the cause and implementing a fix.

The Path Forward: Addressing the Warning

While the warning itself doesn't break the functionality of your chart, it's good practice to address it. Here are a few approaches:

  1. Use the config argument: The warning explicitly suggests this. Instead of passing width='content' directly, you can pass it within the config dictionary. This is the recommended way to handle Plotly-specific configurations going forward.

    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)

# Pass width via the config argument
st.plotly_chart(fig, config={'displayModeBar': False, 'width': 'content'})

    Note: The config dictionary can take various Plotly configuration options, not just width and height. You might need to consult the Plotly documentation for a full list.

  2. Avoid width='content' if possible: If width='content' is not strictly necessary for your layout, and a fixed width or the default behavior is acceptable, you can simply omit it. Streamlit's default behavior often tries to fit the chart within the available container, which might be sufficient.

  3. Pin Streamlit version (temporary): As a temporary workaround, if you cannot immediately refactor your code, you could pin your Streamlit version to one where this regression did not occur. However, this is not a long-term solution and should be avoided if possible.

  4. Contribute to the Streamlit project: If you're comfortable with it, you can report this issue on the Streamlit GitHub repository or even submit a pull request to fix it. Developers are actively working on improving Streamlit, and reporting such issues helps the community.

The most robust solution is to adapt to the recommended config argument. This not only resolves the warning but also aligns your code with the future direction of Streamlit and Plotly integration, ensuring better maintainability and compatibility.

For more in-depth information on Streamlit and Plotly, you can refer to the official documentation: