Close #79: ipywidgets' Widget.comm field now uses Any() instead of In…

…stance()

shinywidgets/_shinywidgets.py

@@ -17,12 +17,13 @@
 from ipywidgets._version import (
     __protocol_version__,  # pyright: ignore[reportUnknownVariableType]
 )
-
 from ipywidgets.widgets.widget import (
     Widget,
     _remove_buffers,  # pyright: ignore[reportUnknownVariableType, reportGeneralTypeIssues]
 )
-from shiny import Session, event, reactive
+import traitlets
+
+from shiny import Session, reactive
 from shiny._utils import run_coro_sync, wrap_async
 from shiny.http_staticfiles import StaticFiles
 from shiny.render import RenderFunction, RenderFunctionAsync
@@ -67,13 +68,16 @@ def init_shiny_widget(w: Widget):
     while hasattr(session, "_parent"):
         session = session._parent
 
-    # `Widget` has `comm = Instance('ipykernel.comm.Comm')` which means we'd get a
-    # runtime error if we try to set this attribute to a different class, but
-    # fortunately this hack provides a workaround.
-    # TODO: find a better way to do this (maybe send a PR to ipywidgets?) or at least clean up after ourselves
-    # https://github.com/jupyter-widgets/ipywidgets/blob/88cec8b/python/ipywidgets/ipywidgets/widgets/widget.py#L424
-    old_comm_klass = copy.copy(Widget.comm.klass)  # type: ignore
-    Widget.comm.klass = object  # type: ignore
+    # Previous versions of ipywidgets (< 8.0.5) had
+    #   `Widget.comm = Instance('ipykernel.comm.Comm')`
+    # which meant we'd get a runtime error when setting `Widget.comm = ShinyComm()`.
+    # In more recent versions, this is no longer necessary since they've (correctly)
+    # changed comm from an Instance() to Any().
+    # https://github.com/jupyter-widgets/ipywidgets/pull/3533/files#diff-522bb5e7695975cba0199c6a3d6df5be827035f4dc18ed6da22ac216b5615c77R482
+    old_comm_klass = None
+    if isinstance(Widget.comm, traitlets.traitlets.Instance):  # type: ignore
+        old_comm_klass = copy.copy(Widget.comm.klass)  # type: ignore
+        Widget.comm.klass = object  # type: ignore
 
     # Get the initial state of the widget
     state, buffer_paths, buffers = _remove_buffers(w.get_state())  # type: ignore
@@ -137,7 +141,8 @@ def _():
         comm.handle_msg(msg)
 
     def _restore_state():
-        Widget.comm.klass = old_comm_klass  # type: ignore
+        if old_comm_klass is not None:
+            Widget.comm.klass = old_comm_klass  # type: ignore
         SESSIONS.remove(session)  # type: ignore
 
     session.on_ended(_restore_state)