Make ypywidgets optional

plugins/kernels/fps_kernels/kernel_driver/driver.py

@@ -181,7 +181,7 @@ async def _handle_iopub(self, msg_id: str, ycell: Map) -> None:
                     ycell["execution_state"] = "idle"
 
     async def _handle_comms(self) -> None:
-        if self.yjs is None:
+        if self.yjs is None or self.yjs.widgets is None:  # type: ignore
             return
 
         while True:
@@ -247,7 +247,7 @@ async def _handle_outputs(self, outputs: Array, msg: Dict[str, Any]):
             if "application/vnd.jupyter.ywidget-view+json" in content["data"]:
                 # this is a collaborative widget
                 model_id = content["data"]["application/vnd.jupyter.ywidget-view+json"]["model_id"]
-                if self.yjs is not None:
+                if self.yjs is not None and self.yjs.widgets is not None:  # type: ignore
                     if model_id in self.yjs.widgets.widgets:  # type: ignore
                         doc = self.yjs.widgets.widgets[model_id]["model"].ydoc  # type: ignore
                         path = f"ywidget:{doc.guid}"

plugins/yjs/fps_yjs/routes.py

@@ -50,7 +50,10 @@ def __init__(
         super().__init__(app=app, auth=auth)
         self.contents = contents
         self.room_manager = RoomManager(contents)
-        self.widgets = Widgets()
+        if Widgets is None:
+            self.widgets = None
+        else:
+            self.widgets = Widgets()  # type: ignore
 
     async def collaboration_room_websocket(
         self,

plugins/yjs/fps_yjs/ywidgets/widgets.py

@@ -1,52 +1,64 @@
+from typing import Any
+
 import pkg_resources
 from pycrdt import TransactionEvent
-from ypywidgets.utils import (  # type: ignore
-    YMessageType,
-    YSyncMessageType,
-    create_update_message,
-    process_sync_message,
-    sync,
-)
-
-
-class Widgets:
-    def __init__(self):
-        self.ydocs = {
-            ep.name: ep.load() for ep in pkg_resources.iter_entry_points(group="ypywidgets")
-        }
-        self.widgets = {}
-
-    def comm_open(self, msg, comm) -> None:
-        target_name = msg["content"]["target_name"]
-        if target_name != "ywidget":
-            return
-
-        name = msg["metadata"]["ymodel_name"]
-        comm_id = msg["content"]["comm_id"]
-        self.comm = comm
-        model = self.ydocs[f"{name}Model"]()
-        self.widgets[comm_id] = {"model": model, "comm": comm}
-        msg = sync(model.ydoc)
-        comm.send(**msg)
-
-    def comm_msg(self, msg) -> None:
-        comm_id = msg["content"]["comm_id"]
-        message = bytes(msg["buffers"][0])
-        if message[0] == YMessageType.SYNC:
-            ydoc = self.widgets[comm_id]["model"].ydoc
-            reply = process_sync_message(
-                message[1:],
-                ydoc,
-            )
-            if reply:
-                self.widgets[comm_id]["comm"].send(buffers=[reply])
-            if message[1] == YSyncMessageType.SYNC_STEP2:
-                ydoc.observe(self._send)
-
-    def _send(self, event: TransactionEvent):
-        update = event.update  # type: ignore
-        message = create_update_message(update)
-        try:
-            self.comm.send(buffers=[message])
-        except Exception:
-            pass
+
+try:
+    from ypywidgets.utils import (  # type: ignore
+        YMessageType,
+        YSyncMessageType,
+        create_update_message,
+        process_sync_message,
+        sync,
+    )
+    ypywidgets_installed = True
+except ImportError:
+    ypywidgets_installed = False
+
+
+Widgets: Any
+
+if ypywidgets_installed:
+    class Widgets:
+        def __init__(self):
+            self.ydocs = {
+                ep.name: ep.load() for ep in pkg_resources.iter_entry_points(group="ypywidgets")
+            }
+            self.widgets = {}
+
+        def comm_open(self, msg, comm) -> None:
+            target_name = msg["content"]["target_name"]
+            if target_name != "ywidget":
+                return
+
+            name = msg["metadata"]["ymodel_name"]
+            comm_id = msg["content"]["comm_id"]
+            self.comm = comm
+            model = self.ydocs[f"{name}Model"]()
+            self.widgets[comm_id] = {"model": model, "comm": comm}
+            msg = sync(model.ydoc)
+            comm.send(**msg)
+
+        def comm_msg(self, msg) -> None:
+            comm_id = msg["content"]["comm_id"]
+            message = bytes(msg["buffers"][0])
+            if message[0] == YMessageType.SYNC:
+                ydoc = self.widgets[comm_id]["model"].ydoc
+                reply = process_sync_message(
+                    message[1:],
+                    ydoc,
+                )
+                if reply:
+                    self.widgets[comm_id]["comm"].send(buffers=[reply])
+                if message[1] == YSyncMessageType.SYNC_STEP2:
+                    ydoc.observe(self._send)
+
+        def _send(self, event: TransactionEvent):
+            update = event.update  # type: ignore
+            message = create_update_message(update)
+            try:
+                self.comm.send(buffers=[message])
+            except Exception:
+                pass
+else:
+    Widgets = None