Streamlit: Fixes Plotly Chart Width Deprecation Warning
If you're a Streamlit user who loves to jazz up your web applications with interactive Plotly charts, you might have stumbled upon a rather pesky deprecation warning recently. Specifically, when using the st.plotly_chart function with width or height parameters set to something like "content", you're likely seeing a warning about variable keyword arguments (kwargs). This is happening even if you're not explicitly passing any extra keyword arguments beyond the documented ones. It’s a bit of a head-scratcher, right? You’re just trying to make your charts fit nicely, and suddenly you’re being told you’re doing something wrong with kwargs! This article is here to dive deep into this issue, explain why it's happening, and how you can navigate it, ensuring your Streamlit applications remain clean and warning-free.
Understanding the plotly_chart Function and kwargs
Let's first get on the same page about what st.plotly_chart does and what kwargs actually are in Python. The st.plotly_chart function is Streamlit's way of seamlessly embedding Plotly figures into your web applications. It's super convenient because it handles a lot of the underlying rendering and communication for you. Now, in Python, kwargs stands for keyword arguments. When you define a function, you can accept an arbitrary number of keyword arguments using **kwargs. This is a flexible way to pass arguments to a function without having to predefine every single parameter. For example, if a function is defined as def my_function(**kwargs):, you could call it like my_function(name='Alice', age=30, city='New York'), and inside the function, kwargs would be a dictionary: {'name': 'Alice', 'age': 30, 'city': 'New York'}. This is powerful for creating adaptable functions.
However, this flexibility comes with a caveat: if a function is designed to accept **kwargs but you're passing arguments that aren't specifically handled or intended by the function's developer, it can lead to confusion or unexpected behavior. This is where the deprecation warning comes into play. Streamlit, in its efforts to keep its API clean and forward-compatible, has been refining how arguments are passed. Previously, it might have been more lenient with accepting various keyword arguments, including those related to chart dimensions. But as the library evolves, they are encouraging developers to use specific, documented parameters instead of relying on the catch-all **kwargs for certain functionalities. This leads us to the specific issue at hand: using width="content" or height="content" in st.plotly_chart seems to be triggering a warning that suggests kwargs are being used improperly, even when you're just using a documented parameter.
It's important to distinguish between explicitly passing kwargs and using documented parameters that might internally be handled via kwargs by the underlying Plotly library or Streamlit's wrapper. The warning users are encountering suggests that Streamlit's internal logic for handling these dimensions is being flagged as a potential misuse of kwargs, leading to the deprecation warning. This is a common scenario in software development where features that were once accepted are being phased out in favor of a more structured approach to prevent future compatibility issues and to guide users towards best practices. The goal is to make the API more predictable and easier to maintain.
The Root of the Warning: How width="content" Triggers kwargs
The core of the problem lies in how Streamlit processes the arguments you pass to st.plotly_chart, particularly when you specify width="content" or height="content". While these are documented and valid ways to control the display size of your Plotly charts (making them adapt to the container's width), Streamlit's internal code might be interpreting these arguments in a way that inadvertently triggers a kwargs deprecation warning. This isn't necessarily a bug in your code, but rather an artifact of how Streamlit's plotly_chart function is implemented and how it interacts with the underlying Plotly library's argument handling. The warning message specifically points to if kwargs: show_deprecation_warning(...), indicating that any presence of kwargs—even if they are intended and documented parameters—is causing the warning to fire.
Think of it like this: Streamlit's st.plotly_chart function acts as an intermediary. It receives your figure and any arguments you pass. When you provide width="content", Streamlit needs to process this instruction and pass it along to the Plotly rendering engine. It's possible that in the process of translating width="content" into instructions that Plotly understands, Streamlit's code is inadvertently treating this or other non-standard arguments as general kwargs. If the internal logic checks for the existence of kwargs before processing other arguments, and if width="content" is somehow being bundled or processed as part of these general kwargs, the warning will appear. This can happen if the function is designed to catch any unexpected keyword arguments and flag them for deprecation, and the width or height parameters, when set to a string like "content", are falling into that category during a specific stage of processing.
Furthermore, Streamlit has been migrating away from certain older argument names and patterns. The warning you're seeing is likely a consequence of this transition. The use_container_width parameter, for instance, was a common way to achieve this responsive sizing, and it has been deprecated in favor of the more versatile width and height arguments. However, the deprecation warning system might be a bit overzealous, flagging any use of what it perceives as kwargs even when the arguments are correctly specified according to the latest documentation. This can be frustrating because it deviates from the expected behavior where documented parameters should not trigger deprecation warnings related to other argument handling mechanisms.
Essentially, the warning is a signal that Streamlit is refining its argument parsing. While width="content" is the correct way to achieve responsive sizing now, the underlying mechanism for detecting unused or potentially problematic kwargs is being tripped by this specific, valid usage. It highlights a subtle edge case in the library's argument handling that needs to be addressed by the Streamlit developers to ensure a smoother user experience.
Reproducing the Issue: A Simple Code Example
To truly understand and confirm this plotly_chart kwargs deprecation warning, it's helpful to see it in action with a straightforward code example. The Streamlit team themselves provided a minimal, reproducible snippet that clearly demonstrates the problem. Let's break down this code and see how it triggers the warning.
import plotly.graph_objects as go
import streamlit as st
# First, we create a basic Plotly figure.
# This is a simple barpolar chart, but the type of chart doesn't really matter for this issue.
fig = go.Figure()
fig.add_trace(go.Barpolar(r=[1], theta=[0], width=[120]))
# We then update the layout with specific dimensions. While these are set here,
# they might be overridden or influenced by the st.plotly_chart arguments.
fig.update_layout(width=500, height=360)
# This is the crucial line that causes the warning.
# We're calling st.plotly_chart and passing the figure.
# Importantly, we're using the 'width="content"' argument.
# This tells Streamlit to make the chart's width adapt to its container.
st.plotly_chart(fig, width="content")
In this script, we import the necessary libraries: plotly.graph_objects for creating the chart and streamlit for displaying it. We initialize a go.Figure and add a simple Barpolar trace to it. Then, we set explicit width and height in the update_layout method. This is standard Plotly practice. The key action happens in the last line: st.plotly_chart(fig, width="content"). Here, we are telling Streamlit to render the fig object, and critically, to set its width to `
