Save widget model state to notebook metadata

Currently default values are not removed and binary buffers are not saved.

(updated to conform to widget state schema)

nbconvert/preprocessors/execute.py

@@ -480,6 +480,7 @@ def run_cell(self, cell, cell_index=0):
                 continue
             elif msg_type.startswith('comm'):
                 self.handle_comm_msg(outs, msg, cell_index)
+                self.widget_state[content['comm_id']] = content['data']['state']
                 continue
 
             display_id = None
@@ -556,3 +557,16 @@ def executenb(nb, cwd=None, km=None, **kwargs):
         resources['metadata'] = {'path': cwd}
     ep = ExecutePreprocessor(**kwargs)
     return ep.preprocess(nb, resources, km=km)[0]
+
+
+def _serialize_widget_state(state):
+    """Serialize a widget state, following format in @jupyter-widgets/schema.
+
+    TODO: Does not currently split binary buffers or remove default values.
+    """
+    return {
+        'model_name': state['_model_name'],
+        'model_module': state['_model_module'],
+        'model_module_version': state.get('_model_module_version'),
+        'state': state,
+    }

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

@@ -0,0 +1,47 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "application/vnd.jupyter.widget-view+json": {
+       "model_id": "c3f75dd69f3e4602989aaa3711d2977d",
+       "version_major": 2,
+       "version_minor": 0
+      },
+      "text/html": [
+       "<p>Failed to display Jupyter Widget of type <code>Label</code>.</p>\n",
+       "<p>\n",
+       "  If you're reading this message in the Jupyter Notebook or JupyterLab Notebook, it may mean\n",
+       "  that the widgets JavaScript is still loading. If this message persists, it\n",
+       "  likely means that the widgets JavaScript library is either not installed or\n",
+       "  not enabled. See the <a href=\"https://ipywidgets.readthedocs.io/en/stable/user_install.html\">Jupyter\n",
+       "  Widgets Documentation</a> for setup instructions.\n",
+       "</p>\n",
+       "<p>\n",
+       "  If you're reading this message in another frontend (for example, a static\n",
+       "  rendering on GitHub or <a href=\"https://nbviewer.jupyter.org/\">NBViewer</a>),\n",
+       "  it may mean that your frontend doesn't currently support widgets.\n",
+       "</p>\n"
+      ],
+      "text/plain": [
+       "Label(value='Hello World')"
+      ]
+     },
+     "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

@@ -57,6 +57,9 @@ 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)
@@ -305,3 +308,33 @@ 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
+        ]
+
+        wdata = output_nb['metadata']['widgets'] \
+                ['application/vnd.jupyter.widget-state+json']
+        for k in model_ids:
+            d = wdata['state'][k]
+            assert 'model_name' in d
+            assert 'model_module' in d
+            assert 'state' in d
+        assert 'version_major' in wdata
+        assert 'version_minor' in wdata

setup.py

@@ -213,7 +213,7 @@ def run(self):
 jupyter_client_req = 'jupyter_client>=4.2'
 
 extra_requirements = {
-    'test': ['pytest', 'pytest-cov', 'ipykernel', jupyter_client_req],
+(??)    'test': ['pytest', 'pytest-cov', 'ipykernel', 'jupyter_client>=4.2'],
     'serve': ['tornado>=4.0'],
     'execute': [jupyter_client_req],
     'docs': ['sphinx>=1.5.1',