feat: Patch ipywidgets to be more flexible with child widgets

anywidget/__init__.py

@@ -2,11 +2,14 @@
 
 from __future__ import annotations
 
+from ._patch_ipywidgets import _patch_ipywidgets
 from ._version import __version__
 from .widget import AnyWidget
 
 __all__ = ["AnyWidget", "__version__"]
 
+_patch_ipywidgets()
+
 
 def _jupyter_labextension_paths() -> list[dict]:
     return [{"src": "labextension", "dest": "anywidget"}]

anywidget/_patch_ipywidgets.py

@@ -0,0 +1,111 @@
+"""ipywidgets patch module.
+
+Patches ipywidgets to allow for more flexible serialization and
+deserialization of (any)widgets by allowing objects that are not
+strict instances of `ipywidgets.Widget`.
+
+Only `ipywidgets.Box` and `ipywidgets.widgets.widget_link.Link`
+give problems. This code is mostly vendored from ipywidgets and
+modified to allow for more flexibility.
+"""
+
+from __future__ import annotations
+
+import typing as t
+
+import ipywidgets
+import traitlets
+from ipywidgets import Widget
+
+from ._descriptor import _COMMS
+
+_IPYWIDGETS_INSTANCES = ipywidgets.widgets.widget._instances
+
+
+def _get_model_id(x: t.Any) -> t.Any:
+    """Get the model id of a widget or comm."""
+    if isinstance(x, Widget):
+        return x.model_id
+    maybe_comm = _COMMS.get(id(x), None)
+    return getattr(maybe_comm, "comm_id", None)
+
+
+def _widget_to_json(x: t.Any, obj: t.Any) -> t.Any:
+    """Recursively convert a widget to json."""
+    if isinstance(x, dict):
+        return {k: _widget_to_json(v, obj) for k, v in x.items()}
+    elif isinstance(x, (list, tuple)):
+        return [_widget_to_json(v, obj) for v in x]
+    model_id = _get_model_id(x)
+    return f"IPY_MODEL_{model_id}" if model_id else x
+
+
+def _json_to_widget(x: t.Any, obj: t.Any) -> t.Any:
+    """Recursively convert json to a widget."""
+    if isinstance(x, dict):
+        return {k: _json_to_widget(v, obj) for k, v in x.items()}
+    elif isinstance(x, (list, tuple)):
+        return [_json_to_widget(v, obj) for v in x]
+    elif (
+        isinstance(x, str)
+        and x.startswith("IPY_MODEL_")
+        and x[10:] in _IPYWIDGETS_INSTANCES
+    ):
+        return _IPYWIDGETS_INSTANCES[x[10:]]
+    else:
+        return x
+
+
+class WidgetTrait(traitlets.TraitType):
+    """Traitlet for validating things that can be (de)serialized into widgets."""
+
+    # anything that can get a model id is ok as a widget
+    def validate(self, obj: t.Any, value: t.Any) -> t.Any:
+        if _get_model_id(value) is not None:
+            return value
+        else:
+            self.error(obj, value)
+
+
+# Adapted from https://github.com/jupyter-widgets/ipywidgets/blob/bb2edf78e7dac26e4b15522a267d7b477026a840/python/ipywidgets/ipywidgets/widgets/widget_link.py#L15
+class WidgetTraitTuple(traitlets.Tuple):
+    """Traitlet for validating a single (Widget, 'trait_name') pair."""
+
+    info_text = "A (Widget, 'trait_name') pair"
+
+    def __init__(self) -> None:
+        super().__init__(WidgetTrait(), traitlets.Unicode())
+
+    def validate_elements(self, obj: t.Any, value: t.Any) -> t.Any:
+        value = super().validate_elements(obj, value)
+        widget, trait_name = value
+        trait = widget.traits().get(trait_name)
+        trait_repr = f"{widget.__class__.__name__}.{trait_name}"
+        # Can't raise TraitError because the parent will swallow the message
+        # and throw it away in a new, less informative TraitError
+        if trait is None:
+            raise TypeError(f"No such trait: {trait_repr}")
+        elif not trait.metadata.get("sync"):
+            raise TypeError(f"{trait_repr} cannot be synced")
+        return value
+
+
+def _patch_ipywidgets() -> None:
+    """Patch ipywidgets to allow for more flexible serialization and deserialization."""
+    ipywidgets.Box.children.metadata["to_json"] = _widget_to_json
+    ipywidgets.Box.children.metadata["from_json"] = _json_to_widget
+    ipywidgets.Box.children.validate = ipywidgets.widgets.trait_types.TypedTuple(
+        WidgetTrait()
+    ).validate
+
+    ipywidgets.widgets.widget_link.Link.source.metadata["to_json"] = _widget_to_json
+    ipywidgets.widgets.widget_link.Link.source.metadata["from_json"] = _json_to_widget
+    ipywidgets.widgets.widget_link.Link.source.validate_elements = (
+        WidgetTraitTuple().validate_elements
+    )
+
+    ipywidgets.widgets.widget_link.Link.target.metadata["to_json"] = _widget_to_json
+    ipywidgets.widgets.widget_link.Link.target.metadata["from_json"] = _json_to_widget
+    ipywidgets.widgets.widget_link.Link.target.validate_elements = (
+        WidgetTraitTuple().validate_elements
+    )