Allow adding ipywidgets to extension in JupyterLab (#3392)

* Allow adding ipywidgets to extension in JupyterLab

* Add ipywidgets to extension

* Update requirements

* Load ipywidgets ext for mpl example

.github/workflows/docs.yaml

@@ -65,7 +65,7 @@ jobs:
           conda install "pip<21.2.1" 
           conda list
           doit develop_install -o doc -o examples
-          pip install pyecharts idom==0.24 ipympl
+          pip install pyecharts idom==0.24
       - name: temporarily pin jinja2
         run: |
           eval "$(conda shell.bash hook)"

examples/reference/panes/IPyWidget.ipynb

@@ -10,18 +10,14 @@
     "import panel as pn\n",
     "import ipywidgets as ipw\n",
     "\n",
-    "pn.extension()"
+    "pn.extension('ipywidgets')"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "The ``IPyWidget`` pane renders any ipywidgets model both in the notebook and in a deployed server. This makes it possible to leverage this growing ecosystem directly from within Panel simply by wrapping the component in a Pane or Panel. However when rendering ipywidgets on the server you may have to initialize the `ipywidgets` extension by running:\n",
-    "\n",
-    "```python\n",
-    "pn.extension('ipywidgets')\n",
-    "```\n",
+    "The ``IPyWidget`` pane renders any ipywidgets model both in the notebook and in a deployed server. This makes it possible to leverage this growing ecosystem directly from within Panel simply by wrapping the component in a Pane or Panel.\n",
     "\n",
     "In the notebook this is not necessary since Panel simply uses the regular notebook ipywidget renderer. Particularly in JupyterLab importing the ipywidgets extension in this way may interfere with the UI and render the JupyterLab UI unusable, so enable the extension with care.\n",
     "\n",

examples/reference/panes/Matplotlib.ipynb

@@ -8,7 +8,7 @@
    "source": [
     "import panel as pn\n",
     "\n",
-    "pn.extension()"
+    "pn.extension('ipywidgets')"
    ]
   },
   {

panel/config.py

@@ -468,6 +468,12 @@ def __call__(self, *args, **params):
         }
         for arg in args:
             if arg in self._imports:
+                try:
+                    if (arg == 'ipywidgets' and get_ipython() and
+                        not "PANEL_IPYWIDGET" in os.environ): # noqa (get_ipython)
+                        continue
+                except Exception:
+                    pass
                 __import__(self._imports[arg])
             elif arg in reactive_exts:
                 ReactiveHTMLMetaclass._loaded_extensions.add(arg)

setup.py

@@ -149,12 +149,14 @@ def run(self):
         'ipywidgets_bokeh',
         'ipyvolume',
         'ipyleaflet',
+        'ipympl',
+        'folium',
         'xarray',
         'pyinstrument >=4.0',
         'aiohttp',
         'croniter',
         'graphviz',
-        'networkx>=2.5',
+        'networkx >=2.5',
         'pygraphviz'
     ],
     'tests': _tests,