fix linter issues

Author: wolfv

docs/source/examples/Drag and Drop examples.ipynb renamed to docs/source/examples/Drag and Drop.ipynb

@@ -16,7 +16,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 1,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -46,7 +46,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "460d334fd7214373bf6512e94b48d350",
+       "model_id": "98fccc59219d44a6b0cb8eae0562b46e",
        "version_major": 2,
        "version_minor": 0
       },
@@ -78,7 +78,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "29b71c8d69c6441e942d03cd4da671e1",
+       "model_id": "65e6ec5eb86b410cbce29f07dd846385",
        "version_major": 2,
        "version_minor": 0
       },
@@ -117,7 +117,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "d3aac4a1f8b846db8e27495d904682b5",
+       "model_id": "c113a1c95285465592ee98227120f597",
        "version_major": 2,
        "version_minor": 0
       },
@@ -150,7 +150,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "c0082b4380d743beabd1397071ec41f6",
+       "model_id": "4af0471abc3a4a5095ca121766948b60",
        "version_major": 2,
        "version_minor": 0
       },
@@ -166,7 +166,7 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "{'text/plain': 'Drag me', 'application/vnd.jupyter.widget-view+json': 'd3aac4a1f8b846db8e27495d904682b5', 'widget': DraggableBox(child=Label(value='Drag me'))}\n"
+      "{'text/plain': 'Drag me', 'application/vnd.jupyter.widget-view+json': 'c113a1c95285465592ee98227120f597', 'widget': DraggableBox(child=Label(value='Drag me'))}\n"
      ]
     }
    ],
@@ -224,7 +224,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "ef9e91fbcd2c45089f8897d72af12845",
+       "model_id": "d4ca90bafedf4a1fa7b2e57d3d2b3387",
        "version_major": 2,
        "version_minor": 0
       },
@@ -259,7 +259,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "58d2f51d1b29455fabe519278478f69f",
+       "model_id": "46ade71e68a0435f81fc7de391d6abba",
        "version_major": 2,
        "version_minor": 0
       },
@@ -299,21 +299,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 9,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "67a49e632f3a48ecb0588ff21910b818",
+       "model_id": "21d9bcd6218447169ffe194cacc120e6",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "DraggableBox(child=Label(value='Drag me'))"
       ]
      },
-     "execution_count": 12,
+     "execution_count": 9,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -327,21 +327,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 10,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "29474f46942d4ecb85b97ca1ee3530e4",
+       "model_id": "715966a4cc4d4edfbd6ba181a08d80bd",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "DropBox(child=VBox(children=(Label(value='Drop here'),)), layout=Layout(height='100px', width='200px'))"
       ]
      },
-     "execution_count": 13,
+     "execution_count": 10,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -381,23 +381,23 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 14,
+   "execution_count": 11,
    "metadata": {
     "scrolled": true
    },
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "bb57d5bec390451d8766fbfb7d1f983f",
+       "model_id": "75e49d2a1548473cb3490dbf8609dc31",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "DraggableBox(child=Label(value='Drag me'), drag_data={'application/custom-data': 'Custom data'})"
       ]
      },
-     "execution_count": 14,
+     "execution_count": 11,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -410,21 +410,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 12,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "c7e766365bf54ac4966d4f03fca04258",
+       "model_id": "8ba49ae0ee34481399031c482cb1debc",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "DropBox(child=Label(value='Drop here'))"
       ]
      },
-     "execution_count": 15,
+     "execution_count": 12,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -468,7 +468,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 13,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -477,21 +477,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 14,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "246675c70be544cf9202e3cdb804f99b",
+       "model_id": "661bd735e4604ac792e10bb609b163d6",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "DraggableBox(child=IntSlider(value=0, description='Drag me', layout=Layout(width='250px')))"
       ]
      },
-     "execution_count": 17,
+     "execution_count": 14,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -503,7 +503,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 15,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -513,21 +513,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 19,
+   "execution_count": 16,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "62af6c1abfa6492c8e6351b4b0ad7f25",
+       "model_id": "26d319118d0e4e16826f4c5ca8ce479e",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "DropBox(child=VBox(children=(Label(value='Drop sliders below'),), layout=Layout(height='150px', width='350px')…"
       ]
      },
-     "execution_count": 19,
+     "execution_count": 16,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -554,7 +554,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 17,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -565,7 +565,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 18,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -588,7 +588,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 19,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -603,21 +603,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 23,
+   "execution_count": 20,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "44b808f2cc8b4e10867545279e833d68",
+       "model_id": "2477925b3bc9403892c7ea797b5fe82f",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "GridspecLayout(children=(DraggableBox(child=Label(value='col1'), drag_data={'data/app': '[4, 2, 1]'}, layout=L…"
       ]
      },
-     "execution_count": 23,
+     "execution_count": 20,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -640,21 +640,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 25,
+   "execution_count": 21,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "f94865838f714367877f60b8ab699426",
+       "model_id": "e0dd3bf734be402a8c93857bb78f773b",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
-       "DropBox(child=Figure(axes=[Axis(scale=LinearScale(), side='bottom'), Axis(orientation='vertical', scale=Linear…"
+       "DropBox(child=Label(value='Drag data from the table and drop it here.'), layout=Layout(height='500px', width='…"
       ]
      },
-     "execution_count": 25,
+     "execution_count": 21,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -679,7 +679,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 26,
+   "execution_count": 22,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -742,21 +742,21 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 27,
+   "execution_count": 23,
    "metadata": {},
    "outputs": [
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "b4a88100b0004784b18acecaedf02e3c",
+       "model_id": "7647ef70e93743fd83a19b916f1bb73c",
        "version_major": 2,
        "version_minor": 0
       },
       "text/plain": [
        "HBox(children=(DraggableBox(child=SelectMultiple(description='Fruits', index=(1,), options=('Apples', 'Oranges…"
       ]
      },
-     "execution_count": 27,
+     "execution_count": 23,
      "metadata": {},
      "output_type": "execute_result"
     }

ipywidgets/widgets/widget_dragdrop.py

@@ -65,18 +65,18 @@ def _handle_dragdrop_msg(self, _, content, buffers):
 class DropBox(DropWidget):
     _model_name = Unicode('DropBoxModel').tag(sync=True)
     _view_name = Unicode('DropBoxView').tag(sync=True)
-    child = Instance(Widget).tag(sync=True, **widget_serialization)
+    child = Instance(Widget, allow_none=True).tag(sync=True, **widget_serialization)
 
-    def __init__(self, child, *args, **kwargs):
-        super(DropBox, self).__init__(*args, **kwargs, child=child)
+    def __init__(self, child=None, **kwargs):
+        super(DropBox, self).__init__(**kwargs, child=child)
 
 @register
 class DraggableBox(DropWidget):
     _model_name = Unicode('DraggableBoxModel').tag(sync=True)
     _view_name = Unicode('DraggableBoxView').tag(sync=True) 
-    child = Instance(Widget).tag(sync=True, **widget_serialization)
+    child = Instance(Widget, allow_none=True).tag(sync=True, **widget_serialization)
     draggable = Bool(True).tag(sync=True)
     drag_data = Dict().tag(sync=True)
 
-    def __init__(self, child, *args, **kwargs):
-        super(DraggableBox, self).__init__(*args, **kwargs, child=child)
+    def __init__(self, child=None, **kwargs):
+        super(DraggableBox, self).__init__(**kwargs, child=child)