From d3a98f06ab519e77bb97e2d8d60ef36cd93f2e68 Mon Sep 17 00:00:00 2001
From: Sanjay Santhanam <51058514+Sanjays2402@users.noreply.github.com>
Date: Thu, 30 Jul 2026 20:19:13 -0700
Subject: [PATCH] fix: don't route non-widget attribute deletion through
 remove()

ContainerWidget.__delattr__ unconditionally called self.remove(name),
so deleting any plain attribute that is not a current child widget
raised ValueError from MutableSequence.remove -- including deleting a
reference to a widget that had already been removed from the container.

__delattr__ now looks for a matching child widget by name and removes it,
otherwise falls back to object.__delattr__, which keeps normal Python
semantics (AttributeError for a name that does not exist).
---
 .../widgets/bases/_container_widget.py         |  8 ++++++--
 tests/test_container.py                        | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/magicgui/widgets/bases/_container_widget.py b/src/magicgui/widgets/bases/_container_widget.py
index 9a2ebc31f..319cdbb0d 100644
--- a/src/magicgui/widgets/bases/_container_widget.py
+++ b/src/magicgui/widgets/bases/_container_widget.py
@@ -341,8 +341,12 @@ def remove(self, value: Widget | str) -> None:
         super().remove(value)  # type: ignore
 
     def __delattr__(self, name: str) -> None:
-        """Delete a widget by name."""
-        self.remove(name)
+        """Delete a widget by name, or a plain attribute if no widget matches."""
+        for widget in self._list:
+            if name == widget.name:
+                self.remove(widget)
+                return
+        object.__delattr__(self, name)
 
     def __delitem__(self, key: int | slice) -> None:
         """Delete a widget by integer or slice index."""
diff --git a/tests/test_container.py b/tests/test_container.py
index 15a85880f..19dbeebb9 100644
--- a/tests/test_container.py
+++ b/tests/test_container.py
@@ -117,6 +117,24 @@ def test_delete_widget():
         container.index(a)
 
 
+def test_delete_non_widget_attribute():
+    """Deleting a plain attribute does not go through widget removal."""
+    a = widgets.Label(name="a")
+    container = widgets.Container(widgets=[a])
+    container.x = 5
+    del container.x
+    assert not hasattr(container, "x")
+
+    # a widget that was already removed can still be dereferenced
+    container.remove(a)
+    container.a_ref = a
+    del container.a_ref
+
+    # a name that is neither a widget nor an attribute still raises AttributeError
+    with pytest.raises(AttributeError):
+        del container.nonexistent
+
+
 def test_reset_choice_recursion():
     """Test that reset_choices recursion works for multiple types of widgets."""
     x = 0