Save widget model state to notebook metadata

Currently default values are not removed

nbconvert/preprocessors/execute.py

@@ -273,12 +273,19 @@ def start_new_kernel(startup_timeout=60, kernel_name='python', **kwargs):
             cwd=path)
         self.kc.allow_stdin = False
         self.nb = nb
+        self.widget_state = {}
 
         try:
             nb, resources = super(ExecutePreprocessor, self).preprocess(nb, resources)
         finally:
             self.kc.stop_channels()
             self.km.shutdown_kernel(now=self.shutdown_kernel == 'immediate')
+            if self.widget_state:
+                self.nb.metadata.widgets = {
+                    'application/vnd.jupyter.widget-state+json': {
+                        'state': self.widget_state
+                    }
+                }
 
         delattr(self, 'nb')
 
@@ -409,6 +416,7 @@ def run_cell(self, cell, cell_index=0):
                         cell_map[cell_index] = []
                 continue
             elif msg_type.startswith('comm'):
+                self.widget_state[content['comm_id']] = content['data']['state']
                 continue
 
             display_id = None

nbconvert/preprocessors/tests/files/widget-hello-world.ipynb

@@ -0,0 +1,32 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "application/vnd.jupyter.widget-view+json": {
+       "model_id": "64111c035eec4e1ab43895db8121e229",
+       "version_major": 2,
+       "version_minor": 0
+      },
+      "text/plain": [
+       "A Jupyter Widget"
+      ]
+     },
+     "metadata": {},
+     "output_type": "display_data"
+    }
+   ],
+   "source": [
+    "import ipywidgets\n",
+    "ipywidgets.Label('Hello World')"
+   ]
+  }
+ ],
+ "metadata": {},
+ "nbformat": 4,
+ "nbformat_minor": 2
+}

nbconvert/preprocessors/tests/test_execute.py

@@ -54,6 +54,9 @@ def normalize_output(output):
         if 'text/plain' in output.get('data', {}):
             output['data']['text/plain'] = \
                 re.sub(addr_pat, '<HEXADDR>', output['data']['text/plain'])
+        if 'application/vnd.jupyter.widget-view+json' in output.get('data', {}):
+            output['data']['application/vnd.jupyter.widget-view+json'] \
+                ['model_id'] = '<MODEL_ID>'
         for key, value in output.get('data', {}).items():
             if isinstance(value, string_types):
                 output['data'][key] = _normalize_base64(value)
@@ -270,3 +273,28 @@ def test_execute_function(self):
         original = copy.deepcopy(input_nb)
         executed = executenb(original, os.path.dirname(filename))
         self.assert_notebooks_equal(original, executed)
+
+    def test_widgets(self):
+        """Runs a test notebook with widgets and checks the widget state is saved."""
+        input_file = os.path.join(current_dir, 'files', 'widget-hello-world.ipynb')
+        opts = dict(kernel_name="python")
+        res = self.build_resources()
+        res['metadata']['path'] = os.path.dirname(input_file)
+        input_nb, output_nb = self.run_notebook(input_file, opts, res)
+
+        output_data = [
+            output.get('data', {})
+            for cell in output_nb['cells']
+            for output in cell['outputs']
+        ]
+
+        model_ids = [
+            data['application/vnd.jupyter.widget-view+json']['model_id']
+            for data in output_data
+            if 'application/vnd.jupyter.widget-view+json' in data
+        ]
+
+        widget_state = output_nb['metadata']['widgets'] \
+                       ['application/vnd.jupyter.widget-state+json']['state']
+        for k in model_ids:
+            assert k in widget_state