No error bubbling?

Hi, if an exception is thrown during an interactive action, such as a callback invoked by Canvas.on_mouse_down, there seems to be no way of knowing this.

e.g.:

from ipycanvas import Canvas

def callback(*args):
    raise ValueError("Invisible")

c = Canvas(size=(500, 500))
c.on_mouse_down(callback)
c

by contrast, errors in ipywidgets.Button calls are reported in the jupyter lab log:

from ipywidgets import Button
b = Button(description='Hi')

def callback(*args):
    raise ValueError("Invisible")

b.on_click(callback)
b

Is it possible to match this behaviour?

[kenseehart]

Here’s my workaround:

import traceback

class MyUI:
    def __init__(self, canvas, model):
        self.canvas = canvas
        self.model = model
        canvas.on_mouse_down(self.mouse_down)

    def mouse_down(self, x, y):
        try:
            do_some_stuff()
        except:
            self.print_traceback()
            
    def print_traceback(self):
        self.canvas.fill_style = '#ff8888'
        self.canvas.fill_rect(10, 10, 300, 300)
        self.canvas.fill_style = '#000000'
        s = traceback.format_exc()
        for i, si in enumerate(s.split('\n')):
            canvas.fill_text(si, 20, 30+15*i)    

Works great. Now my code is debugable.

[janfreyberg]

that’s a really neat workaround, thanks @kenseehart