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name: plotly-figurewidget-interactive description: "Fix for Plotly FigureWidget KeyError: 'uid' when updating shapes with sliders. Trigger: interactive Plotly dashboard errors, FigureWidget batch_update issues" author: Claude Code date: 2026-01-06

Plotly FigureWidget Interactive Dashboard Fix

Experiment Overview

Item	Details
Date	2026-01-06
Goal	Create interactive QC dashboard with linked threshold sliders using Plotly FigureWidget
Environment	Python 3.12, Plotly 6.5.0, ipywidgets 8.1.8, VS Code Jupyter
Status	Success (after multiple fixes)

Context

Building an interactive single-cell QC dashboard with:

• Multiple linked plots (histograms, scatter plots, pie chart)
• Threshold sliders that update all plots simultaneously
• Threshold lines on plots that move with slider values

Encountered multiple issues with Plotly FigureWidget in VS Code environment.

Verified Workflow

Working Pattern: Recreate Figure on Update

The most reliable approach for VS Code is to recreate the entire figure on each slider change rather than trying to update an existing FigureWidget:

import plotly.graph_objects as go
from plotly.subplots import make_subplots
import plotly.io as pio
import ipywidgets as widgets
from IPython.display import display, clear_output

# Set renderer for VS Code compatibility
pio.renderers.default = "notebook"

# Pre-compute data (do this once outside the update function)
hist_data = np.histogram(values, bins=100)
scatter_x = data_x[subsample_mask]
scatter_y = data_y[subsample_mask]

def create_figure(threshold1, threshold2):
    """Create fresh figure with current threshold values."""
    fig = make_subplots(rows=1, cols=2)

    # Add traces
    fig.add_trace(go.Bar(x=hist_data[1][:-1], y=hist_data[0]), row=1, col=1)
    fig.add_trace(go.Scattergl(x=scatter_x, y=scatter_y, mode='markers'), row=1, col=2)

    # Add threshold lines as shapes
    shapes = [
        dict(type='line', x0=threshold1, x1=threshold1, y0=0, y1=1,
             yref='y domain', xref='x', line=dict(color='red', dash='dash'))
    ]
    fig.update_layout(shapes=shapes, height=600, width=1000)

    return fig

# Create sliders
slider1 = widgets.FloatSlider(value=50, min=0, max=100, description='Threshold:')

# Output widget for figure
fig_output = widgets.Output()

def update_dashboard(change=None):
    fig = create_figure(slider1.value, slider2.value)
    with fig_output:
        clear_output(wait=True)
        fig.show()

# Connect sliders
slider1.observe(update_dashboard, names='value')

# Display
display(slider1)
display(fig_output)
update_dashboard()  # Initial render

Failed Attempts (Critical)

Attempt	Why it Failed	Lesson Learned
FigureWidget + batch_update() for shapes	KeyError: 'uid' in _handler_js2py_traceDeltas	Plotly 6.x bug: don't modify shapes inside batch_update()
Modify shapes list in place	Same KeyError: 'uid'	The bug triggers when ANY shape modification happens during batch sync
Update shapes outside batch_update()	Shapes update but traces don't sync	Partial fix - shapes work but other updates may lag
Just display(FigureWidget) in VS Code	Figure doesn't render (blank output)	VS Code renderer issues with FigureWidget
fig.show() without Output widget	Multiple overlapping figures on each update	Need clear_output(wait=True) in Output widget

Root Cause Analysis

The KeyError: 'uid' error occurs in Plotly 6.x when:

1. FigureWidget is used with interactive updates
2. Shapes are modified (even outside batch_update())
3. The JavaScript-to-Python trace delta sync tries to access a uid field that doesn't exist

The bug is in plotly/basewidget.py:445:

def _handler_js2py_traceDeltas(self, change):
    for delta in trace_deltas:
        trace_uid = delta["uid"]  # KeyError here when delta lacks 'uid'

Final Parameters

# Plotly configuration for VS Code
import plotly.io as pio
pio.renderers.default = "notebook"  # or "vscode"

# Figure dimensions
fig.update_layout(
    height=700,
    width=1100
)

# Subsample for performance with large datasets
n_points = min(50000, len(data))

Key Insights

• FigureWidget is fragile: In Plotly 6.x with VS Code, FigureWidget has multiple rendering and sync issues
• Recreate > Update: For interactive dashboards, recreating the entire figure on each update is more reliable than trying to update in place
• Use Output widget: Wrap fig.show() in widgets.Output() with clear_output(wait=True) to prevent stacking
• Pre-compute expensive operations: Histograms and data subsampling should happen once, not on every update
• Subsample large datasets: Scatter plots with >50k points will lag; subsample for interactivity

Alternative Approaches

If you need true in-place updates (e.g., streaming data):

# Option 1: Use Dash instead of Jupyter widgets
# Option 2: Use Panel library which has better widget support
# Option 3: Downgrade to Plotly 5.x where FigureWidget is more stable

References

• Plotly FigureWidget documentation: https://plotly.com/python/figurewidget/
• Related issue: https://github.com/plotly/plotly.py/issues/3441
• ipywidgets Output widget: https://ipywidgets.readthedocs.io/en/stable/examples/Output%20Widget.html