Fixed title formatter in GenericElementPlot (#4061)

* fixed indentation mistake

* moved general part of _format_title into DimensionedPlot

* add deprecation warning

* friendlier deprecation warning

* tests for NdLayout and Element

holoviews/plotting/plot.py

@@ -486,6 +486,42 @@ def _frame_title(self, key, group_size=2, separator='\n'):
         return util.bytes_to_unicode(separator.join(g for g in groups if g))
 
 
+    def _format_title(self, key, dimensions=True, separator='\n'):
+        if self.title_format and util.config.future_deprecations:
+            self.param.warning('title_format is deprecated. Please use title instead')
+
+        label, group, type_name, dim_title = self._format_title_components(
+            key, dimensions=True, separator='\n'
+        )
+
+        custom_title = (self.title != self.param.params('title').default)
+        if custom_title and self.title_format:
+            self.warning('Both title and title_format set. Using title')
+        title_str = (
+            self.title if custom_title or self.title_format is None
+            else self.title_format
+        )
+
+        title = util.bytes_to_unicode(title_str).format(
+            label=util.bytes_to_unicode(label),
+            group=util.bytes_to_unicode(group),
+            type=type_name,
+            dimensions=dim_title
+        )
+        return title.strip(' \n')
+
+
+    def _format_title_components(self, key, dimensions=True, separator='\n'):
+        """
+        Determine components of title as used by _format_title method.
+
+        To be overridden in child classes.
+
+        Return signature: (label, group, type_name, dim_title)
+        """
+        return (self.label, self.group, type(self).__name__, '')
+
+
     def _fontsize(self, key, label='fontsize', common=True):
         if not self.fontsize: return {}
 
@@ -1242,33 +1278,19 @@ def _get_axis_labels(self, dimensions, xlabel=None, ylabel=None, zlabel=None):
         return xlabel, ylabel, zlabel
 
 
-    def _format_title(self, key, dimensions=True, separator='\n'):
+    def _format_title_components(self, key, dimensions=True, separator='\n'):
         frame = self._get_frame(key)
         if frame is None: return None
         type_name = type(frame).__name__
         group = frame.group if frame.group != type_name else ''
         label = frame.label
 
-        if self.layout_dimensions:
+        if self.layout_dimensions or dimensions:
             dim_title = self._frame_title(key, separator=separator)
-            title = dim_title
         else:
-            if dimensions:
-                dim_title = self._frame_title(key, separator=separator)
-            else:
-                dim_title = ''
-
-            custom_title = (self.title != self.param.params('title').default)
-            if custom_title and self.title_format:
-                self.warning('Both title and title_format set. Using title_format parameter')
-
-            title = self.title if custom_title or self.title_format is None else self.title_format
-            title_format = util.bytes_to_unicode(title)
-            title = title_format.format(label=util.bytes_to_unicode(label),
-                                        group=util.bytes_to_unicode(group),
-                                        type=type_name,
-                                        dimensions=dim_title)
-        return title.strip(' \n')
+            dim_title = ''
+
+        return (label, group, type_name, dim_title)
 
 
     def update_frame(self, key, ranges=None):
@@ -1655,24 +1677,13 @@ def _get_frame(self, key):
         return layout_frame
 
 
-    def _format_title(self, key, dimensions=True, separator='\n'):
+    def _format_title_components(self, key, dimensions=True, separator='\n'):
         dim_title = self._frame_title(key, 3, separator) if dimensions else ''
         layout = self.layout
         type_name = type(self.layout).__name__
         group = util.bytes_to_unicode(layout.group if layout.group != type_name else '')
         label = util.bytes_to_unicode(layout.label)
-
-
-        custom_title = (self.title != self.param.params('title').default)
-        if custom_title and self.title_format:
-            self.warning('Both title and title_format set. Using title parameter')
-        title_str = self.title if custom_title or self.title_format is None else self.title_format
-
-        title = util.bytes_to_unicode(title_str).format(label=label,
-                                                        group=group,
-                                                        type=type_name,
-                                                        dimensions=dim_title)
-        return title.strip(' \n')
+        return (label, group, type_name, dim_title)
 
 
 class GenericLayoutPlot(GenericCompositePlot):

holoviews/tests/plotting/bokeh/testelementplot.py

@@ -8,6 +8,7 @@
 from holoviews.element import Curve, Image, Scatter, Labels
 from holoviews.streams import Stream, PointDraw
 from holoviews.plotting.util import process_cmap
+from holoviews.util import render
 
 from .testplot import TestBokehPlot, bokeh_renderer
 from ...utils import LoggingComparisonTestCase
@@ -101,6 +102,17 @@ def test_element_yaxis_right_bare(self):
         self.assertEqual(yaxis.major_tick_line_color, None)
         self.assertTrue(yaxis in plot.state.right)
 
+    def test_element_title_format(self):
+        title_str = ('Label: {label}, group: {group}, '
+                     'dims: {dimensions}, type: {type}')
+        e = Scatter(
+            [],
+            label='the_label',
+            group='the_group',
+        ).opts(title=title_str)
+        title = 'Label: the_label, group: the_group, dims: , type: Scatter'
+        self.assertEqual(render(e).title.text, title)
+
     def test_element_xformatter_string(self):
         curve = Curve(range(10)).options(xformatter='%d')
         plot = bokeh_renderer.get_plot(curve)

holoviews/tests/plotting/bokeh/testlayoutplot.py

@@ -1,15 +1,18 @@
+import re
+
 import numpy as np
 
 from holoviews.core import (HoloMap, GridSpace, Layout, Empty, Dataset,
-                            NdOverlay, DynamicMap, Dimension)
-from holoviews.element import Curve, Image, Points, Histogram
+                            NdOverlay, NdLayout, DynamicMap, Dimension)
+from holoviews.element import Curve, Image, Points, Histogram, Scatter
 from holoviews.streams import Stream
+from holoviews.util import render, opts
 
 from .testplot import TestBokehPlot, bokeh_renderer
 
 try:
     from bokeh.layouts import Column, Row
-    from bokeh.models import Div, ToolbarBox, GlyphRenderer, Tabs, Panel, Spacer, GridBox
+    from bokeh.models import Div, ToolbarBox, GlyphRenderer, Tabs, Panel, Spacer, GridBox, Title
     from bokeh.plotting import Figure
 except:
     pass
@@ -40,6 +43,39 @@ def test_layout_title(self):
                 'font-weight:bold;font-size:12pt">Default: 0</span>')
         self.assertEqual(title.text, text)
 
+    def test_layout_title_format(self):
+        title_str = ('Label: {label}, group: {group}, '
+                     'dims: {dimensions}, type: {type}')
+        layout = NdLayout(
+            {'Element 1': Scatter(
+                [],
+                label='ONE',
+                group='first',
+            ), 'Element 2': Scatter(
+                [],
+                label='TWO',
+                group='second',
+            )},
+            kdims='MYDIM',
+            label='the_label',
+            group='the_group',
+        ).opts(opts.NdLayout(title=title_str), opts.Scatter(title=title_str))
+        # Title of NdLayout
+        title = bokeh_renderer.get_plot(layout).handles['title']
+        self.assertIsInstance(title, Div)
+        text = 'Label: the_label, group: the_group, dims: , type: NdLayout'
+        self.assertEqual(re.split('>|</', title.text)[1], text)
+        # Titles of subplots
+        plot = render(layout)
+        titles = {
+            title.text for title in list(plot.select({'type': Title}))
+        }
+        titles_correct = {
+            'Label: ONE, group: first, dims: MYDIM: Element 1, type: Scatter',
+            'Label: TWO, group: second, dims: MYDIM: Element 2, type: Scatter',
+        }
+        self.assertEqual(titles_correct, titles)
+
     def test_layout_title_fontsize(self):
         hmap1 = HoloMap({a: Image(np.random.rand(10,10)) for a in range(3)})
         hmap2 = HoloMap({a: Image(np.random.rand(10,10)) for a in range(3)})