Add dragging behaviour properties to sliders

[ibdafna]

This PR adds functionality requested in #2832 . The drag behaviour API has been exposed on the python side and now allows four selections:

1. Tap (current default behaviour)
2. Snap (new option)
3. Drag-tap (new default behaviour for all sliders - no change in behaviour for non-range sliders)
4. Drag-snap

There are no breaking API changes, but a new behaviour attribute has been added to the python side.

[jasongrout]

This PR adds functionality requested in #2683 .

#2832, right?

I was thinking it might be better to start out with just changing the default behavior to 'drag-tap', which addresses the user request, and not expose changing it to the users just yet. The tradeoff here is that increasing API surface means we ought to support it in the future (even if we change slider), so it becomes a maintenance burden. On the other hand, it might be useful enough to users to have a tap/snap/drag-snap behavior available. Are there usecases people actually see that do not want drag-tap behavior?

Thoughts? I know I've become very conservative about extending the core ipywidgets api because it aims to be very stable over a long term, so I'm wary of adding maintenance burdens.

[jasongrout]

If exposing this behavior to the users is the way we want to go, then I think you've done a great job here (just reading the code, I haven't run it yet)

[ibdafna]

This PR adds functionality requested in #2683 .

#2832, right?

Indeed. Updated the PR note above with the correct one, thanks for spotting!

I was thinking it might be better to start out with just changing the default behavior to 'drag-tap', which addresses the user request, and not expose changing it to the users just yet. The tradeoff here is that increasing API surface means we ought to support it in the future (even if we change slider), so it becomes a maintenance burden. On the other hand, it might be useful enough to users to have a tap/snap/drag-snap behavior available. Are there usecases people actually see that do not want drag-tap behavior?

Potentially yes. Off the top of my head, let's say I'm using the range slider to control the spot range of a vanilla option payoff at expiry. I would probably not want to drag both handles of the slider at the same time given I am only looking to focus on the strike area. But then again, it might be convenient to drag the full range if I got the original parameters wrong and need to shift my window left or right.

Thoughts? I know I've become very conservative about extending the core ipywidgets api because it aims to be very stable over a long term, so I'm wary of adding maintenance burdens.

I'm definitely with you on robustness. I added the snap behaviour because I often expected the slider handles to behave that way and thought other users might also appreciate that option. If you think we are incurring potential technical debt down the line then I'm happy to remove the changes!

[vidartf]

If you think we are incurring potential technical debt down the line then I'm happy to remove the changes!

We could also consider to "expose" it as an underscore param _behavior ("use at own risk"). 🤷‍♂

[ibdafna]

@jasongrout How should we proceed?

[jtpio]

For folks wanting to try this PR on Binder:

https://mybinder.org/v2/gh/ibdafna/ipywidgets/drag_behaviour?urlpath=lab/tree/docs/source/examples/

[jtpio]

Commenting here as this came up during the weekly meeting today, with @ianhi spotting this attribute was not in American English:

Suggested change

	behaviour : str
	behavior : str

[jtpio]

Ah that was probably because of noUISlider using behaviour in the options:

https://refreshless.com/nouislider/slider-options/#section-limit

[jtpio]

FYI @ibdafna I rebased and added a commit to rename behaviour to behavior (American English)

[ibdafna]

@jtpio thank you 😄