Defined Dimension.step and used it for dynamic widgets

holoviews/core/dimension.py

@@ -149,6 +149,11 @@ class Dimension(param.Parameterized):
         may be an inbuilt constructor (such as int, str, float) or a
         custom class object.""")
 
+    step = param.Number(default=None, doc="""
+        Optional floating point step specifying how frequently the
+        underlying space should be sampled. May be used to define a
+        discrete sampling of over the range.""")
+
     unit = param.String(default=None, allow_None=True, doc="""
         Optional unit string associated with the Dimension. For
         instance, the string 'm' may be used represent units of meters

holoviews/plotting/bokeh/widgets.py

@@ -114,6 +114,8 @@ def create_widget(self, dim, holomap=None, editable=False):
                 int_type = isinstance(dim.type, type) and issubclass(dim.type, int)
                 if isinstance(dim_range, int) or int_type:
                     step = 1
+                elif dim.step is not None:
+                    step = dim.step
                 else:
                     step = 10**((round(math.log10(dim_range))-3))
                 if editable:

holoviews/plotting/widgets/__init__.py

@@ -302,6 +302,8 @@ def get_widgets(self):
                     int_type = isinstance(dim.type, type) and issubclass(dim.type, int)
                     if isinstance(dim_range, int) or int_type:
                         step = 1
+                    elif dim.step is not None:
+                        step = dim.step
                     else:
                         step = 10**(round(math.log10(dim_range))-3)
                     init_dim_vals.append(dim_vals[0])

tests/testbokehwidgets.py

@@ -47,6 +47,19 @@ def test_bokeh_server_dynamic_range_float(self):
         self.assertEqual(label.value, '3.1')
         self.assertIs(mapping, None)
 
+    def test_bokeh_server_dynamic_range_float_step(self):
+        dim = Dimension('x', range=(3.1, 11.2), step=0.1)
+        widget, label, mapping = BokehServerWidgets.create_widget(dim, editable=True)
+        self.assertIsInstance(widget, Slider)
+        self.assertEqual(widget.value, 3.1)
+        self.assertEqual(widget.start, 3.1)
+        self.assertEqual(widget.end, 11.2)
+        self.assertEqual(widget.step, 0.1)
+        self.assertIsInstance(label, TextInput)
+        self.assertEqual(label.title, dim.pprint_label)
+        self.assertEqual(label.value, '3.1')
+        self.assertIs(mapping, None)
+
     def test_bokeh_server_dynamic_range_not_editable(self):
         dim = Dimension('x', range=(3.1, 11.2))
         widget, label, mapping = BokehServerWidgets.create_widget(dim, editable=False)