API change proposal for ipywidget's interact

[Sylvain Corlay]

Hello,

Brian and Fernando advised that I send a message to the mailing list regarding this change.

Both Jupyter and Sage's interactive widget libraries provide an `@interact` function decorator which introspects the arguments of the function to create a simple GUI for interacting with it. Sage and Jupyter APIs for `@interact` are very similar, but differ in how they use abbreviations.

Abbreviations are a way to map default values to a type of widget. For example in both cases the following case

    @interact
    def foo(x=(0, 100, 2)):
        print(x)

both Jupyter and Sage will create a slider with from 0 to 100 with a step of 2. 

In fact, Jupyter and Sage's uses of abbreviations differ in the following way:

• With Sage: When passing a list of items, the generated widget is always a selection widget.
  When passing a tuple of 2 or 3 numerical values, a slider is created and the values are interpreted as(min, max[, step])

• With Jupyter, a selection widget is only used when passing sequence (tuple or list) of strings. 
  A slider is used when passing a sequence of 2 or 3 numerical values, and these values are interpreted as (min, max[, step]).
  

I personally prefer the API of Sage over the one of Jupyter. In my opinion, the type mapping `tuple -> slider` and `list -> selection` is simpler to reason about than a behavior that depends on the type of the items in a sequence.

Obviously, since the two APIs are not compatible, we cannot support them both at the same time. If we decide that we eventually want to adopt the Sage approach, I proposed a way to achieve a smooth transition in the pull request https://github.com/ipython/ipywidgets/pull/288. The proposed change is backward compatible with the Jupyter approach and introduces deprecation warnings when using a list of 2/3 numerical values to create a slider or if the user creates a selection widget with a tuple of strings.

The question to the list is: what do you think of adopting the same type abbreviations as Sage in Jupyter's interact?

Thanks,

Sylvain 

[Matthias Bussonnier]

Hi all, 

This was sent on jupyter ML, but as it’s a Python-kernel only change, it might be good to CC IPython-dev, 

which I do there. 

Please keep a single thread, preferably on Jupyter groups as the thread was started there. 

Thanks

-- 

M

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