Basic widget button to display text on press does not work

[IanMatthewHuff]

btn = widgets.Button(description='Medium')
display(btn)
def btn_eventhandler(obj):
print('Hello from the {} button!'.format(obj.description))
btn.on_click(btn_eventhandler)

In VSCode pressing the button does nothing.

[greazer]

Another example

from ipywidgets import widgets
lbl1 = widgets.Label('')
display(lbl1)
txt1 = widgets.Text()
txt1

Note that the label will not display unless it's not empty.

[rchiodo]

Root cause is how output is wrapped in jupyter. We don't do this wrapping.

Essentially all io_pub messages are routed to an output wrapper during widget creation.

In this code here (inside the widget manager that jupyter has):

setViewOptions(options) {
        var options = options || {};
        if (!options.output && options.parent) {
            // use the parent output if we don't have one
            options.output = options.parent.options.output;
        }
        if (options.output) {
            options.iopub_callbacks = {
                output: options.output.handle_output.bind(options.output),
                clear_output: options.output.handle_clear_output.bind(options.output)
            }
        }
        return options;
    };

We might be able to do something similar were we remap all output etc to a custom output widget we stick below everything else?

[jasongrout]

Note that classic Notebook and JupyterLab handle this differently. When a widget view generates a comm message that causes output:

• classic Jupyter Notebook appends the output to the output of the cell which contained the view
• JupyterLab logs the output in its log console (new in JupyterLab 1.2)

There has been quite a bit of discussion about these behaviors: jupyter-widgets/ipywidgets#2380, sagemathinc/cocalc#3854

[rchiodo]

Thanks @jasongrout, I'm thinking we'll probably not fix this before we ship.

[jasongrout]

Until JupyterLab 1.2, we silently discarded such output messages, and we had lots of complaints. One particular problem is that it discards not only print messages, but also error messages, so debugging a callback that throws an error becomes hard.

A workaround for users is to use an Output widget to capture output.

[jasongrout]

I thought vscode had logging capabilities already built in? It may be useful to surface uncaptured output somewhere so the user at least sees error messages, etc. For example, here is where we send them to the jlab log console: https://github.com/jupyter-widgets/ipywidgets/blob/master/packages/jupyterlab-manager/src/plugin.ts#L181-L199

[rchiodo]

Thanks. That would likely be a good workaround for now. We do log a lot of stuff to our developer console though. We'd likely have to put this somewhere else.

I'm thinking the 'jupyter' output tab might be a good spot.

[IanMatthewHuff]

@rchiodo Should this be validated? I validated the workaround here. But that's just a workaround. Are we ever looking at supporting this? Or should I just close the item?

[rchiodo]

Yeah that was our decision. We can't fix this without doing the same thing jupyter notebooks do. Jupyter labs is not going to support this either.