Add num and round parameters to Float sliders

docs/source/examples/Widget List.ipynb

@@ -47,7 +47,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### IntSlider  \n",
+    "### IntSlider\n",
     "- The slider is displayed with a specified, initial `value`. Lower and upper bounds are defined by `min` and `max`, and the value can be incremented according to the `step` parameter.\n",
     "- The slider's label is defined by `description` parameter \n",
     "- The slider's `orientation` is either 'horizontal' (default) or 'vertical'\n",
@@ -84,7 +84,9 @@
     }
    },
    "source": [
-    "### FloatSlider  "
+    "### FloatSlider\n",
+    "- In addition to the `step` parameter, float sliders (`FloatSlider`, `FloatLogSlider` and `FloatRangeSlider`) also accept a `num` parameter, which specifies the number of values in the `[min, max]` interval. `num` takes precedence over `step`, and ensures that the `max` value is always included (which might not be the case due to floating point precision issues if the `step` parameter is used).\n",
+    "- A `round` parameter allows to round values that are set from the Python side to the closest value in the set of possible values. If `round` is `True`, values will be silently rounded (default value is `False`)."
    ]
   },
   {

ipywidgets/widgets/tests/test_interaction.py

@@ -8,6 +8,7 @@
 import os
 from collections import OrderedDict
 import pytest
+from math import isclose
 
 import ipywidgets as widgets
 
@@ -44,7 +45,13 @@ def check_widget(w, **d):
             assert w.__class__ is expected
         else:
             value = getattr(w, attr)
-            assert value == expected, "{}.{} = {!r} != {!r}".format(w.__class__.__name__, attr, value, expected)
+            def strict_isequal(a, b, rel_tol=None):
+                return a == b
+            if isinstance(value, float):
+                isequal = isclose
+            else:
+                isequal = strict_isequal
+            assert isequal(value, expected, rel_tol=1e-10), "{}.{} = {!r} != {!r}".format(w.__class__.__name__, attr, value, expected)
 
             # For numeric values, the types should match too
             if isinstance(value, (int, float)):

ipywidgets/widgets/widget_float.py

@@ -7,7 +7,7 @@
 # Distributed under the terms of the Modified BSD License.
 
 from traitlets import (
-    Instance, Unicode, CFloat, Bool, CaselessStrEnum, Tuple, TraitError, validate, default
+    Instance, Unicode, CFloat, CInt, Bool, CaselessStrEnum, Tuple, TraitError, validate, default
 )
 from .widget_description import DescriptionWidget
 from .trait_types import InstanceDict, NumberFormat
@@ -153,6 +153,12 @@ class FloatSlider(_BoundedFloat):
         maximal position of the slider
     step : float
         step of the trackbar
+    num : integer
+        number of values in the [min, max] interval, takes precedence over
+        the step parameter
+    round : bool
+        default is False, round the value set from Python to the closest value
+        in the interval
     description : str
         name of the slider
     orientation : {'horizontal', 'vertical'}
@@ -167,6 +173,8 @@ class FloatSlider(_BoundedFloat):
     _view_name = Unicode('FloatSliderView').tag(sync=True)
     _model_name = Unicode('FloatSliderModel').tag(sync=True)
     step = CFloat(0.1, allow_none=True, help="Minimum step to increment the value").tag(sync=True)
+    num = CInt(help="Number of values in the [min, max] interval").tag(sync=True)
+    round = Bool(False, help="Round the value set from Python to the closest value in the interval").tag(sync=True)
     orientation = CaselessStrEnum(values=['horizontal', 'vertical'],
         default_value='horizontal', help="Vertical or horizontal.").tag(sync=True)
     readout = Bool(True, help="Display the current value of the slider next to it.").tag(sync=True)
@@ -177,6 +185,33 @@ class FloatSlider(_BoundedFloat):
 
     style = InstanceDict(SliderStyle).tag(sync=True, **widget_serialization)
 
+    @validate('value')
+    def _validate_value(self, proposal):
+        value = super()._validate_value(proposal)
+        if not self.round:
+            return value
+        # round value to closest one in interval
+        values = [self.min]
+        while values[-1] <= self.max:
+            values.append(values[-1] + self.step)
+        rounded_value = min(values, key=lambda x:abs(x-value))
+        return rounded_value
+
+    @validate('num')
+    def _validate_num(self, proposal):
+        # step value is computed from num
+        # num is not used in the front-end
+        num = proposal['value']
+        if self.min == self.max:
+            if num != 1:
+                raise TraitError('num must be 1 because min == max')
+            self.step = 0
+        elif num <= 1:
+            raise TraitError('num must be greater than 1')
+        else:
+            self.step = (self.max - self.min) / (num - 1)
+        return num
+
 
 @register
 class FloatLogSlider(_BoundedLogFloat):
@@ -194,6 +229,12 @@ class FloatLogSlider(_BoundedLogFloat):
         maximal position of the slider in log scale, i.e., actual maximum is base ** max
     step : float
         step of the trackbar, denotes steps for the exponent, not the actual value
+    num : integer
+        number of values in the [min, max] interval, takes precedence over
+        the step parameter
+    round : bool
+        default is False, round the value set from Python to the closest value
+        in the interval
     description : str
         name of the slider
     orientation : {'horizontal', 'vertical'}
@@ -208,6 +249,8 @@ class FloatLogSlider(_BoundedLogFloat):
     _view_name = Unicode('FloatLogSliderView').tag(sync=True)
     _model_name = Unicode('FloatLogSliderModel').tag(sync=True)
     step = CFloat(0.1, allow_none=True, help="Minimum step in the exponent to increment the value").tag(sync=True)
+    num = CInt(help="Number of values in the [min, max] interval").tag(sync=True)
+    round = Bool(False, help="Round the value set from Python to the closest value in the interval").tag(sync=True)
     orientation = CaselessStrEnum(values=['horizontal', 'vertical'],
         default_value='horizontal', help="Vertical or horizontal.").tag(sync=True)
     readout = Bool(True, help="Display the current value of the slider next to it.").tag(sync=True)
@@ -219,6 +262,33 @@ class FloatLogSlider(_BoundedLogFloat):
 
     style = InstanceDict(SliderStyle).tag(sync=True, **widget_serialization)
 
+    @validate('value')
+    def _validate_value(self, proposal):
+        value = super()._validate_value(proposal)
+        if not self.round:
+            return value
+        # round value to closest one in interval
+        values = [self.min]
+        while values[-1] <= self.max:
+            values.append(values[-1] + self.step)
+        rounded_value = min(values, key=lambda x:abs(x-value))
+        return rounded_value
+
+    @validate('num')
+    def _validate_num(self, proposal):
+        # step value is computed from num
+        # num is not used in the front-end
+        num = proposal['value']
+        if self.min == self.max:
+            if num != 1:
+                raise TraitError('num must be 1 because min == max')
+            self.step = 0
+        elif num <= 1:
+            raise TraitError('num must be greater than 1')
+        else:
+            self.step = (self.max - self.min) / (num - 1)
+        return num
+
 
 @register
 class FloatProgress(_BoundedFloat):
@@ -337,6 +407,11 @@ class FloatRangeSlider(_BoundedFloatRange):
         maximal position of the slider
     step : float
         step of the trackbar
+    num : integer
+        number of values in the [min, max] interval, takes precedence over
+        the step parameter
+    round : bool
+        default is False, round the value set from Python to the closest value
     description : str
         name of the slider
     orientation : {'horizontal', 'vertical'}
@@ -351,6 +426,8 @@ class FloatRangeSlider(_BoundedFloatRange):
     _view_name = Unicode('FloatRangeSliderView').tag(sync=True)
     _model_name = Unicode('FloatRangeSliderModel').tag(sync=True)
     step = CFloat(0.1, allow_none=True, help="Minimum step to increment the value").tag(sync=True)
+    num = CInt(help="Number of values in the [min, max] interval").tag(sync=True)
+    round = Bool(False, help="Round the value set from Python to the closest value in the interval").tag(sync=True)
     orientation = CaselessStrEnum(values=['horizontal', 'vertical'],
         default_value='horizontal', help="Vertical or horizontal.").tag(sync=True)
     readout = Bool(True, help="Display the current value of the slider next to it.").tag(sync=True)
@@ -360,3 +437,30 @@ class FloatRangeSlider(_BoundedFloatRange):
     disabled = Bool(False, help="Enable or disable user changes").tag(sync=True)
 
     style = InstanceDict(SliderStyle).tag(sync=True, **widget_serialization)
+
+    @validate('value')
+    def _validate_value(self, proposal):
+        value = super()._validate_value(proposal)
+        if not self.round:
+            return value
+        # round value to closest one in interval
+        values = [self.min]
+        while values[-1] <= self.max:
+            values.append(values[-1] + self.step)
+        rounded_value = min(values, key=lambda x:abs(x-value))
+        return rounded_value
+
+    @validate('num')
+    def _validate_num(self, proposal):
+        # step value is computed from num
+        # num is not used in the front-end
+        num = proposal['value']
+        if self.min == self.max:
+            if num != 1:
+                raise TraitError('num must be 1 because min == max')
+            self.step = 0
+        elif num <= 1:
+            raise TraitError('num must be greater than 1')
+        else:
+            self.step = (self.max - self.min) / (num - 1)
+        return num

packages/schema/jupyterwidgetmodels.latest.md

@@ -461,9 +461,11 @@ Attribute        | Type             | Default          | Help
 `layout`         | reference to Layout widget | reference to new instance | 
 `max`            | number (float)   | `4.0`            | Max value for the exponent
 `min`            | number (float)   | `0.0`            | Min value for the exponent
+`num`            | number (integer) | `0`              | Number of values in the [min, max] interval
 `orientation`    | string (one of `'horizontal'`, `'vertical'`) | `'horizontal'`   | Vertical or horizontal.
 `readout`        | boolean          | `true`           | Display the current value of the slider next to it.
 `readout_format` | string           | `'.3g'`          | Format for the readout
+`round`          | boolean          | `false`          | Round the value set from Python to the closest value in the interval
 `step`           | `null` or number (float) | `0.1`            | Minimum step in the exponent to increment the value
 `style`          | reference to SliderStyle widget | reference to new instance | 
 `tabbable`       | `null` or boolean | `null`           | Is widget tabbable?
@@ -509,9 +511,11 @@ Attribute        | Type             | Default          | Help
 `layout`         | reference to Layout widget | reference to new instance | 
 `max`            | number (float)   | `100.0`          | Max value
 `min`            | number (float)   | `0.0`            | Min value
+`num`            | number (integer) | `0`              | Number of values in the [min, max] interval
 `orientation`    | string (one of `'horizontal'`, `'vertical'`) | `'horizontal'`   | Vertical or horizontal.
 `readout`        | boolean          | `true`           | Display the current value of the slider next to it.
 `readout_format` | string           | `'.2f'`          | Format for the readout
+`round`          | boolean          | `false`          | Round the value set from Python to the closest value in the interval
 `step`           | `null` or number (float) | `0.1`            | Minimum step to increment the value
 `style`          | reference to SliderStyle widget | reference to new instance | 
 `tabbable`       | `null` or boolean | `null`           | Is widget tabbable?
@@ -535,9 +539,11 @@ Attribute        | Type             | Default          | Help
 `layout`         | reference to Layout widget | reference to new instance | 
 `max`            | number (float)   | `100.0`          | Max value
 `min`            | number (float)   | `0.0`            | Min value
+`num`            | number (integer) | `0`              | Number of values in the [min, max] interval
 `orientation`    | string (one of `'horizontal'`, `'vertical'`) | `'horizontal'`   | Vertical or horizontal.
 `readout`        | boolean          | `true`           | Display the current value of the slider next to it.
 `readout_format` | string           | `'.2f'`          | Format for the readout
+`round`          | boolean          | `false`          | Round the value set from Python to the closest value in the interval
 `step`           | `null` or number (float) | `0.1`            | Minimum step to increment the value
 `style`          | reference to SliderStyle widget | reference to new instance | 
 `tabbable`       | `null` or boolean | `null`           | Is widget tabbable?