add spinner widget (#368)

* add spinner widget

* change low and high to start and end

examples/reference/widgets/Spinner.ipynb

@@ -0,0 +1,95 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import panel as pn\n",
+    "\n",
+    "pn.extension()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "The ``Spinner`` widget allows selecting a value using a spinbox. It behaves like a slider except lower and upper bounds are optionals and a specific value can be entered\n",
+    "\n",
+    "For more information about listening to widget events and laying out widgets refer to the [widgets user guide](../../user_guide/Widgets.ipynb). Alternatively you can learn how to build GUIs by declaring parameters independently of any specific widgets in the [param user guide](../../user_guide/Param.ipynb). To express interactivity entirely using Javascript without the need for a Python server take a look at the [links user guide](../../user_guide/Param.ipynb).\n",
+    "\n",
+    "#### Parameters:\n",
+    "\n",
+    "For layout and styling related parameters see the [customization user guide](../../user_guide/Customization.ipynb).\n",
+    "\n",
+    "##### Core\n",
+    "\n",
+    "* **``value``** (float or int): The initial value of the spinner\n",
+    "* **``step``** (float or int): The step added or subtracted to the current value\n",
+    "* **``start``** (float or int): Optional minimum allowable value\n",
+    "* **``end``** (float or int): Optional maximum allowable value\n",
+    "\n",
+    "##### Display\n",
+    "\n",
+    "* **``disabled``** (boolean): Whether the widget is editable\n",
+    "* **``name``** (str): The title of the widget"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "spinner = pn.widgets.Spinner(name='Spinner', value=5., step=1e-1, start=0, end=10)\n",
+    "\n",
+    "spinner"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "The ``Spinner.value`` returns a float or int value:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "spinner.value"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.7.2"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}

panel/widgets/__init__.py

@@ -8,7 +8,7 @@
 from .button import Button, Toggle # noqa
 from .input import ( # noqa
     ColorPicker, Checkbox, DatetimeInput, DatePicker, FileInput,
-    LiteralInput, StaticText, TextInput)
+    LiteralInput, StaticText, TextInput, Spinner)
 from .misc import Audio # noqa
 from .player import DiscretePlayer, Player # noqa
 from .slider import ( # noqa
@@ -17,4 +17,4 @@
 from .select import ( # noqa
     AutocompleteInput, CheckBoxGroup, CheckButtonGroup, CrossSelector,
     MultiSelect, RadioButtonGroup, RadioBoxGroup, Select, ToggleGroup)
-    
+

panel/widgets/input.py

@@ -14,14 +14,14 @@
 
 from bokeh.models.widgets import (
     CheckboxGroup as _BkCheckboxGroup, ColorPicker as _BkColorPicker,
-    DatePicker as _BkDatePicker, Div as _BkDiv, TextInput as _BkTextInput)
+    DatePicker as _BkDatePicker, Div as _BkDiv, TextInput as _BkTextInput,
+    Spinner as _BkSpinner)
 
 from ..models import FileInput as _BkFileInput
 from ..util import as_unicode
 from .base import Widget
 
 
-
 class TextInput(Widget):
 
     value = param.String(default='', allow_None=True)
@@ -129,6 +129,25 @@ class ColorPicker(Widget):
     _rename = {'value': 'color', 'name': 'title'}
 
 
+class Spinner(Widget):
+
+    start = param.Number(default=None, doc="""
+        Optional minimum allowable value""")
+
+    end = param.Number(default=None, doc="""
+        Optional maximum allowable value""")
+
+    value = param.Number(default=0, doc="""
+        The initial value of the spinner""")
+
+    step = param.Number(default=1, doc="""
+        The step added or subtracted to the current value""")
+
+    _widget_type = _BkSpinner
+
+    _rename = {'name': 'title', 'start': 'low', 'end': 'high'}
+
+
 class LiteralInput(Widget):
     """
     LiteralInput allows declaring Python literals using a text