feat: support nbagg matplotlib backend (WIP)

nbclient/client.py

@@ -24,6 +24,7 @@
 )
 from .util import run_sync, ensure_async
 from .output_widget import OutputWidget
+from .matplotlib import MatplotlibCommHandler
 
 
 def timestamp():
@@ -293,7 +294,8 @@ def __init__(self, nb, km=None, **kw):
         }
         # comm_open_handlers should return an object with a .handle_msg(msg) method or None
         self.comm_open_handlers = {
-            'jupyter.widget': self.on_comm_open_jupyter_widget
+            'jupyter.widget': self.on_comm_open_jupyter_widget,
+            'matplotlib': self.on_comm_open_matplotlib
         }
 
     def reset_execution_trackers(self):
@@ -914,6 +916,12 @@ def on_comm_open_jupyter_widget(self, msg):
             if widget_class:
                 return widget_class(comm_id, state, self.kc, self)
 
+    def on_comm_open_matplotlib(self, msg):
+        content = msg['content']
+        data = content['data']
+        return MatplotlibCommHandler(comm_id=content['comm_id'], kernel_client=self.kc,
+                                     parent_header=msg['parent_header'], nbagg_id=data['id'])
+
 
 def execute(nb, cwd=None, km=None, **kwargs):
     """Execute a notebook's code, updating outputs within the notebook object.

nbclient/matplotlib.py

@@ -0,0 +1,47 @@
+import json
+
+from .jsonutil import json_clean
+
+
+class MatplotlibCommHandler:
+    def __init__(self, comm_id, kernel_client, parent_header, nbagg_id):
+        self.comm_id = comm_id
+        self.kernel_client = kernel_client
+        self.parent_header = parent_header
+        self.nbagg_id = nbagg_id
+
+        # mimics https://github.com/matplotlib/matplotlib/blob/002b27e352b90410c9840233b6ce42c54e291403/lib/matplotlib/backends/web_backend/js/mpl.js#L63  # noqa
+        self.send('{"value":false,"type":"supports_binary","figure_id":"%s"}' % nbagg_id)
+        self.send('{"type":"send_image_mode","figure_id":"%s"}' % nbagg_id)
+        self.send('{"dpi_ratio":2,"type":"set_dpi_ratio","figure_id":"%s"}' % nbagg_id)
+        self.send('{"type":"refresh","figure_id":"%s"}' % nbagg_id)
+
+    def _publish_msg(self, msg_type, data=None, metadata=None, buffers=None, **keys):
+        """Helper for sending a comm message on IOPub"""
+        data = {} if data is None else data
+        metadata = {} if metadata is None else metadata
+        content = json_clean(dict(data=data, comm_id=self.comm_id, **keys))
+        # it seems from looking at the websocket output in Chrome, that parent header
+        # is always empty
+        msg = self.kernel_client.session.msg(msg_type, content=content, parent={},
+                                             metadata=metadata)
+        print("SEND", msg)
+        self.kernel_client.shell_channel.send(msg)
+
+    def send(self, data=None, metadata=None, buffers=None):
+        self._publish_msg('comm_msg', data=data, metadata=metadata, buffers=buffers)
+
+    def handle_msg(self, msg):
+        print("RECV", msg)
+        content = msg['content']
+        data = content['data']
+        nbagg_data = data.get('data')
+        if nbagg_data:
+            nbagg_data = json.loads(nbagg_data)
+            print(nbagg_data)
+            if nbagg_data.get('type') == 'refresh':
+                # cannot figure out when we should send this
+                self.send('{"type":"refresh","figure_id":"%s"}' % self.nbagg_id)
+            if nbagg_data.get('type') == 'resize':
+                # mimics https://github.com/matplotlib/matplotlib/blob/002b27e352b90410c9840233b6ce42c54e291403/lib/matplotlib/backends/web_backend/js/mpl.js#L354  # noqa
+                self.send('{"type":"draw","figure_id":"%s"}' % self.nbagg_id)