Allow for the model_id property to still be accessed after the widget is closed (#179)

Author: cpsievert

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [UNRELEASED] - 2025-01-23
 
 * Fixed an issue with plotly graphs sometimes not getting fully removed from the DOM. (#178)
+* Fixed an issue with ipyleaflet erroring out when attempting to read the `.model_id` property of a closed widget object. (#179)
 
 ## [0.4.2] - 2024-12-18
 

shinywidgets/_comm.py

@@ -1,4 +1,5 @@
 from base64 import b64encode
+from dataclasses import dataclass
 from typing import Callable, Dict, List, Optional
 
 from shiny._utils import run_coro_hybrid
@@ -196,3 +197,30 @@ def handle_msg(self, msg: Dict[str, object]) -> None:
     def handle_close(self, msg: Dict[str, object]) -> None:
         if self._close_callback is not None:
             self._close_callback(msg)
+
+
+@dataclass
+class OrphanedShinyComm:
+    """
+    A 'mock' `ShinyComm`. It's only purpose is to allow one to get
+    the `model_id` (i.e., `comm_id`) of a widget after closing it.
+    """
+
+    comm_id: str
+
+    def send(
+        self,
+        *args: object,
+        **kwargs: object,
+    ) -> None:
+        pass
+
+    def close(
+        self,
+        *args: object,
+        **kwargs: object,
+    ) -> None:
+        pass
+
+    def on_msg(self, callback: MsgCallback) -> None:
+        pass

shinywidgets/_shinywidgets.py

@@ -25,7 +25,7 @@
 
 from ._as_widget import as_widget
 from ._cdn import SHINYWIDGETS_CDN_ONLY, SHINYWIDGETS_EXTENSION_WARNING
-from ._comm import BufferType, ShinyComm, ShinyCommManager
+from ._comm import BufferType, OrphanedShinyComm, ShinyComm, ShinyCommManager
 from ._dependencies import require_dependency
 from ._render_widget_base import has_current_context
 from ._utils import package_dir
@@ -134,7 +134,16 @@ def _cleanup_session_state():
         def on_close():
             with session_context(session):
                 w.close()
-                
+                # By closing the widget, we also close the comm, which sets w.comm to
+                # None. Unfortunately, the w.model_id property looks up w.comm.comm_id
+                # at runtime, and some packages like ipyleaflet want to use this id
+                # to manage references between widgets.
+                w.comm = OrphanedShinyComm(id)
+                # Assigning a comm has the side-effect of adding back a reference to
+                # the widget instance, so remove it again
+                if id in WIDGET_INSTANCE_MAP:
+                    del WIDGET_INSTANCE_MAP[id]
+
         ctx.on_invalidate(on_close)
 
     # Keep track of what session this widget belongs to (so we can close it when the