Add compositional reprs

[philippjfr]

An initial implementation of compositional reprs, which can be improved later.

Some sample outputs for moderately complex dashboards include:

Row(
    HTML(str, width=200),
    Spacer(width=30),
    ParamMethod(method),
    Spacer(width=50),
    Column(
        Param(ParameterSets, name='Attractors', width=220),
        Param(Attractors, expand=True, name='Options', width=220)
    )
)

Column(
    Row(
        Markdown(str, width=170),
        Spacer(width=50),
        Column(
            Markdown(str, height=25, width=400),
            Spacer(height=-15),
            Markdown(str, width=500)
        ),
        Spacer(width=180),
        Column(
            HoloViews(DynamicMap),
            Button(name='Clear selection'),
            Spacer(height=-15)
        ),
        Markdown(str, width=80)
    ),
    Spacer(height=-50),
    Row(
        HoloViews(DynamicMap),
        HoloViews(DynamicMap)
    ),
    Row(
        HoloViews(DynamicMap),
        HoloViews(DynamicMap)
    )
)

• Implements Supply compositional reprs #125

[codecov-io]

Codecov Report

Merging #129 into master will increase coverage by 0.3%.
The diff coverage is 94.62%.

@@            Coverage Diff            @@
##           master     #129     +/-   ##
=========================================
+ Coverage   89.63%   89.94%   +0.3%     
=========================================
  Files          27       27             
  Lines        4034     4196    +162     
=========================================
+ Hits         3616     3774    +158     
- Misses        418      422      +4

Impacted Files	Coverage Δ
panel/tests/test_widgets.py	100% <100%> (ø)	⬆️
panel/tests/test_util.py	100% <100%> (ø)	⬆️
panel/tests/test_panes.py	94.93% <100%> (+0.09%)	⬆️
panel/util.py	74.4% <100%> (+3.45%)	⬆️
panel/param.py	90.54% <100%> (+0.26%)	⬆️
panel/pane.py	81.84% <100%> (+0.3%)	⬆️
panel/tests/test_param.py	99.62% <100%> (ø)	⬆️
panel/tests/test_layout.py	100% <100%> (ø)	⬆️
panel/viewable.py	69.41% <77.77%> (+0.22%)	⬆️
panel/layout.py	97.28% <82.35%> (+0.21%)	⬆️
... and 1 more

---

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[jbednar]

That's a good start, thanks! I'd rather avoid the parentheses after Column and Row; this is not an eval-able expression, and I think it's better to make that clear (and avoid the extra whitespace).

The representation also doesn't yet achieve indicating how to index into this object, which is a feature of HoloViews reprs that I really find helpful. For that it would need to have numbers on the Row and Column entries to indicate which how to index the whole structure to reach that part. But of course implementing that can be postponed...

[philippjfr]

How's this:

Column
    [0] Row
        [0] Markdown(str, width=170)
        [1] Spacer(width=50)
        [2] Column
            [0] Markdown(str, height=25, width=400)
            [1] Spacer(height=-15)
            [2] Markdown(str, width=500)
        [3] Spacer(width=180)
        [4] Column
            [0] HoloViews(DynamicMap)
            [1] Button(name='Clear selection')
            [2] Spacer(height=-15)
        [5] Markdown(str, width=80)
    [1] Spacer(height=-50)
    [2] Row
        [0] HoloViews(DynamicMap)
        [1] HoloViews(DynamicMap)
    [3] Row
        [0] HoloViews(DynamicMap)
        [1] HoloViews(DynamicMap)

[jbednar]

Looks fabulous to me! I can super easily now pull out [0][5] and work with it!

[jbednar]

I can't wait to update my interact() example to demonstrate how and why interact() is now a clear starting point, not a dead end!

[jbednar]

I think we need to limit the reprs:

Column
    [0] WidgetBox
        [0] FloatSlider(end=2, name='a', start=-2, value=1.7)
        [1] FloatSlider(end=2, name='b', start=-2, value=1.7)
        [2] FloatSlider(end=2, name='c', start=-2, value=0.6)
        [3] FloatSlider(end=2, name='d', start=-2, value=1.2)
        [4] IntSlider(end=20000000, name='n', start=1, value=2000000)
        [5] Select(name='colormap', options={'bgy': ['#fff123', '#fff122', '#fff122', '#fff022',
'#fff021', '#fcf021', '#f9f021', '#f5f021', '#f2f020', '#eef020', '#eaef20', '#e7ef20', '#e3ef1f',
'#dfef1f', '#dcee1f', '#d8ee1f', '#d4ee1e', '#d1ee1e', '#cded1e', '#c9ed1e', '#c6ed1e', '#c2ec1d',
'#beec1d', '#bbec1d', '#b7eb1d', '#b3eb1d', '#b0ea1c', '#acea1c', '#a8ea1c', '#a4e91c', '#a1e91c',
'#9de81c', '#99e81c', '#95e71b', '#91e71b', '#8ee61b', '#8ae61b', '#86e51b', '#82e51b', '#7ee41b',
'#7ae31b', '#76e31a', '#72e21a', '#6ee21a', '#6ae11a', '#66e01a', '#62e01a', '#5edf1a', '#5ade1a',
... 5 pages of output ...
'#0b017e', '#0a017c', '#09017a', '#090178', '#080276', '#070274', '#060272', '#060270', '#05026e', 
'#04026c', '#030269', '#030267', '#020265', '#010263', '#010261', '#00025f', '#00025d', '#00025b', 
'#000259', '#000257', '#000255', '#000154', '#000152', '#000150', '#00004e'])
    [1] interactive(function, manual_name=Run Interact)

[philippjfr]

I think we need to limit the reprs:

Yes, I'll add a function to generate shortened reprs for parameter values.

[philippjfr]

@jbednar Mind playing around a bit?

[jbednar]

Looks great to me:

Column
    [0] WidgetBox
        [0] FloatSlider(end=2, name='a', start=-2, value=1.7)
        [1] FloatSlider(end=2, name='b', start=-2, value=1.7)
        [2] FloatSlider(end=2, name='c', start=-2, value=0.6)
        [3] FloatSlider(end=2, name='d', start=-2, value=1.2)
        [4] IntSlider(end=20000000, name='n', start=1, value=2000000)
        [5] Select(name='colormap', options={'bgy': ['#fff123', ...}, value=['#b3fef5', '#b0fef5', ...])
    [1] interactive(function, manual_name='Run Interact')