readout_format fails silently

[adwasser]

IPython version 6.1.0

Any improper string input for the readout_format keyword argument of FloatSlider is associated with the interactive failing to display, without any indication that the readout_format input is bad.

Is there a way to warn users about this?

[pbugnion]

Thanks for raising an issue. For reference, this is still broken on current master. The view throws when it renders.

For a minimal example:

import ipywidgets as widgets
widgets.FloatSlider(1.0, readout_format='broken')

This is the line that causes the exception.

@jasongrout Do you think the solution to this is to define a more specific traitlet for the readout format, or to somehow expose the exception thrown by the JS client in the Python layer?

[jasongrout]

define a more specific traitlet for the readout format

I like this more than trying to push errors back to python. Is there a nice regex for these formats? What if we had a string traitlet that validated based on a regex?

[jasongrout]

(Marking as Future, but if someone submits a PR in time for 7.0, that's great too)

[pbugnion]

What if we had a string traitlet that validated based on a regex?

This seems useful. The bulk of the parsing is done by a regex.

Marking as Future, but if someone submits a PR in time for 7.0, that's great too

Happy to take a look at this over the weekend, unless someone else gets there first.

[jasongrout]

Fixed in #1550.