plotly / plotly/plotly.py

Multiple traces in a FigureWidget break callbacks

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bug P3
Dominant language
Python
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Description

Hello!
I am using

plotly 5.7.0
jupyterlab 3.3.2
ipywidgets 7.7.0
(these are the latest versions of each package)

I am not using Dash.
What I am trying to achieve is a simple FigureWidget with two scatter plots in it, each with a callback that prints the element the user has clicked on. However, the callbacks are fired incorrectly. The trace object given to the callback function is always the last added trace, not the one that the user clicked on.

Here is a minimal example which I adapted from the official documentation (https://plotly.com/python/click-events/#update-points-using-a-click-callback)

import plotly.graph_objects as go
from ipywidgets import Output
import numpy as np
import ipywidgets

np.random.seed(1)

scatter_1 = go.Scatter(x=np.random.rand(100), y=np.random.rand(100), mode='markers', hovertext="hello, I am scatter 1", marker={"symbol": "triangle-up", "size": 10, "color": "red"},)
scatter_2 = go.Scatter(x=np.random.rand(100), y=np.random.rand(100), mode='markers', hovertext="hello, I am scatter 2", marker={"symbol": "triangle-down", "size": 10, "color": "blue"},)

f = go.FigureWidget()
f.add_trace(scatter_1)
f.add_trace(scatter_2)
f.layout.hovermode = 'closest'

f

This correctly renders the figure:
Screen Shot 2022-04-12 at 16 32 48

Then, I add a callback, one to each trace, by manipulating f.data:

o = ipywidgets.Output()

@o.capture(clear_output=True)  
def callback(trace, points, selector):
    print(trace)
    print(points)
    print(selector)
        
f.data[0].on_click(callback)
f.data[1].on_click(callback)

o

Clicking a blue triangle works, it correctly shows the clicked trace and point:
Screen Shot 2022-04-12 at 16 35 08

Clicking a red triangle yields wrong output. The point object is somehow empty, and the trace object is wrong (trace 1 even though trace 0 was clicked):
Screen Shot 2022-04-12 at 16 35 16

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the two-trace FigureWidget example with plotly 5.7.0, JupyterLab 3.3.2, and ipywidgets 7.7.0. Start by tracing the f.data[i].on_click(callback) handling and compare callbacks for the first and last traces. Done means clicking either trace reports the clicked trace and point correctly.

Written by the indexing model from the issue text.

Assessment

Tech stack
jupyter-notebook, python
Domain
data-visualization
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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