Add Children for Box (and subclasses) to support validation of any type of iterable plus a configurable option to omit invalid items (including closed widgets) and log a warning or error.

Author: Alan Fleming

python/ipywidgets/ipywidgets/widgets/widget_box.py

@@ -1,3 +1,4 @@
+
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 
@@ -7,14 +8,16 @@
 group other widgets together and control their
 relative layouts.
 """
+from __future__ import annotations
+
+import typing
+
+from traitlets import CaselessStrEnum, TraitError, TraitType, Unicode
 
-from .widget import register, widget_serialization, Widget
+from .docutils import doc_subst
 from .domwidget import DOMWidget
+from .widget import Widget, register, widget_serialization
 from .widget_core import CoreWidget
-from .docutils import doc_subst
-from .trait_types import TypedTuple
-from traitlets import Unicode, CaselessStrEnum, Instance
-
 
 _doc_snippets = {}
 _doc_snippets['box_params'] = """
@@ -25,8 +28,35 @@
         one of 'success', 'info', 'warning' or 'danger', or ''.
         Applies a predefined style to the box. Defaults to '',
         which applies no pre-defined style.
+
+    validate_mode: str 
+        one of 'raise', 'warning', error'.
+        How invalid children will be treated.
+        'raise' will raise a trait error.
+        'warning' and 'error' will log an error using box.log dropping
+        the invalid items from children.
 """
 
+class Children(TraitType['tuple[Widget,...]', typing.Iterable[Widget]]):
+    default_value = ()
+
+    def validate(self, obj: Box, value: typing.Iterable[Widget]):
+        valid, invalid = [], []
+        for v in value:
+            if isinstance(v, Widget) and v._repr_mimebundle_:
+                valid.append(v)
+            else:
+                invalid.append(v)
+        if invalid:
+            msg = f'Invalid or closed items found: {invalid}'
+            if obj.validate_mode == 'log_warning':
+                obj.log.warning(msg)
+            elif obj.validate_mode == 'log_error':
+                obj.log.error(msg)
+            else:
+                raise TraitError(msg)
+        return tuple(valid)
+
 
 @register
 @doc_subst(_doc_snippets)
@@ -48,19 +78,23 @@ class Box(DOMWidget, CoreWidget):
     """
     _model_name = Unicode('BoxModel').tag(sync=True)
     _view_name = Unicode('BoxView').tag(sync=True)
+    tooltip = Unicode('', allow_none=True, help='A tooltip caption.').tag(sync=True)
+    validate_mode = CaselessStrEnum(['raise', 'log_warning', 'log_error'], 'raise')
 
     # Child widgets in the container.
     # Using a tuple here to force reassignment to update the list.
     # When a proper notifying-list trait exists, use that instead.
-    children = TypedTuple(trait=Instance(Widget), help="List of widget children").tag(
-        sync=True, **widget_serialization)
+    children = Children(help='List of widget children').tag(
+        sync=True, **widget_serialization
+    )
 
     box_style = CaselessStrEnum(
         values=['success', 'info', 'warning', 'danger', ''], default_value='',
         help="""Use a predefined styling for the box.""").tag(sync=True)
-
+    
     def __init__(self, children=(), **kwargs):
-        kwargs['children'] = children
+        if children:
+            kwargs['children'] = children
         super().__init__(**kwargs)
 
 @register