Fixed title formatter in GenericElementPlot

[poplarShift]

Before:

After:

This said, I would also like to point out that the _format_title methods of GenericElementPlot and GenericCompositePlot look pretty similar, and both classes directly derive from DimensionedPlot, yet when both title and title_format are set, one falls back to title, the other one to title_format. I don't know if there was a special reason why the two classes have separate implementations but I think the code could potentially be clearer.

from holoviews import opts
import holoviews as hv
hv.extension('bokeh')
# hv.extension('matplotlib')

l = hv.NdLayout({'FOO': hv.Scatter([], group='ONE'), 'BAR': hv.Scatter([], label='TWO')}, kdims='MYDIM').opts(
    opts.Scatter(title_format='this {label} is {group} my {dimensions} formatter')
)
l

[DancingQuanta]

This is great! I was about to use title_format until I saw this. Is this case already covered in test suite?

[poplarShift]

Hm, I didn't check actually. (I wanted to wait for feedback on whether we should simplify the title/title_format arguments while we're at it but I guess that can be done later too.)

[philippjfr]

So the idea was that title would eventually replace title_format entirely and they were just aliases. Therefore title should at least for now take precedence. So if we could combine the two implementations in some form and have title take precedence in both cases that would be great.

[poplarShift]

Ok I'm having a look at combining the two.

[poplarShift]

Done @philippjfr. MWE to play around with it:

from holoviews import opts
import holoviews as hv
hv.extension('bokeh')

options = [
    opts.Scatter(title='this {label} is {group} my {dimensions} formatter', frame_width=400),
    opts.NdLayout(title='LAYOUT TITLE: this {label} is {group} my {dimensions} formatter'),
    opts.NdOverlay(title='OVERLAY TITLE: this {label} is {group} my {dimensions} formatter')
]
foo = hv.Scatter([], group='ONE', label='first')
bar = hv.Scatter([], group='TWO', label='second')
l = hv.NdLayout({'FOO': foo, 'BAR': bar}, kdims='MYDIM').opts(*options).cols(1).relabel(group='spam', label='eggs')
l

[philippjfr]

Thanks! Looking much better to me. Any chance of adding some tests?

[philippjfr]

Oh I'm also happy to start adding a deprecation warning for title_format, maybe leaving it behind a hv.config.future_deprecations flag for now.

[poplarShift]

I'll look at the tests later. I guess we'd need some for a simple Element, a Layout, and an Overlay, and for all backends? (The code should not depend on backend so one could get away with only one I guess.)

[philippjfr]

(The code should not depend on backend so one could get away with only one I guess.)

That seems fine.

[poplarShift]

I've added tests for the bokeh backend.