Added support for selecting lists and dicts

[jbednar]

Selector widgets currently need to do a reverse lookup on object identity, which requires that objects be hashable, which Bokeh palettes (as lists) are not. This PR and a matching PR on param converts lists to tuples when doing lookups, which works:

import panel as pp
from colorcet import kbc, fire
pp.extension()

def fn(a=1.7, cmap=kbc):
    return a,cmap[0]

pp.interact(fn, cmap=[kbc,fire])

import param

class C(param.Parameterized):
    a = param.Number(1.7, bounds=(-2, 2))
    cmap = param.ObjectSelector(kbc,[kbc,fire])

    def view(self):
        return self.a, self.cmap[0]
c=C()
pp.Row(c.param,c.view)

However, note that in both cases the representation of the list is vastly larger than the widget box, which in the second example ends before (2, '#000000') starts. @philippjfr, is there a way to truncate the representation in the widget when it's longer than the box?

For a Param-based widget the solution is to provide string names, but I'm not sure how to do that with interact:

class C(param.Parameterized):
    a = param.Number(1.7, bounds=(-2, 2))
    cmap = param.ObjectSelector(kbc,dict(kbc=kbc,fire=fire))

    def view(self):
        return self.a, self.cmap[0]
c=C()
pp.Row(c.param,c.view)

[codecov-io]

Codecov Report

Merging #50 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #50      +/-   ##
==========================================
+ Coverage   91.14%   91.22%   +0.07%     
==========================================
  Files          23       23              
  Lines        2925     2950      +25     
==========================================
+ Hits         2666     2691      +25     
  Misses        259      259

Impacted Files	Coverage Δ
panel/param.py	91.25% <100%> (ø)	⬆️
panel/tests/test_widgets.py	100% <100%> (ø)	⬆️
panel/widgets.py	97.54% <100%> (+0.05%)	⬆️

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[philippjfr]

Looks good. Want to add a unit test? 😄

[jbednar]

Also added support for selecting dicts:

import param

theme1 = dict(a=2,c=5)
theme2 = dict(a=5,c=2)

class C(param.Parameterized):
    a = param.Number(1.7, bounds=(-2, 2))
    theme = param.ObjectSelector(theme1,{"1":theme1,"2":theme2})

    def view(self):
        return self.a, self.theme
c=C()
pp.Row(c.param,c.view)

[jbednar]

For a Param-based widget the solution is to provide string names, but I'm not sure how to do that with interact

Actually, the same solution works with interact too:

import panel as pp
from colorcet import kbc, fire
pp.extension()

def fn(a=1.7, cmap=kbc):
    return a,cmap[0]

pp.interact(fn, cmap=dict(kbc=kbc,fire=fire))

So it is still an error that the widget extends outside the widget box, but at least there's a workaround that's arguably the right thing to do anyway (use string names for any complex objects).