Add weakref with opt in automatic widget deletion using 'enable_weakreference'.

Author: Alan Fleming

python/ipywidgets/ipywidgets/widgets/__init__.py

@@ -1,7 +1,7 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 
-from .widget import Widget, CallbackDispatcher, register, widget_serialization
+from .widget import Widget, CallbackDispatcher, register, widget_serialization, enable_weakreference, disable_weakreference
 from .domwidget import DOMWidget
 from .valuewidget import ValueWidget
 

python/ipywidgets/ipywidgets/widgets/tests/test_widget.py

@@ -3,17 +3,21 @@
 
 """Test Widget."""
 
+import copy
+import gc
 import inspect
+import weakref
 
 import pytest
 from IPython.core.interactiveshell import InteractiveShell
 from IPython.display import display
 from IPython.utils.capture import capture_output
 
+import ipywidgets as ipw
+
 from .. import widget
 from ..widget import Widget
 from ..widget_button import Button
-import copy
 
 
 def test_no_widget_view():
@@ -88,4 +92,169 @@ def test_widget_copy():
     with pytest.raises(NotImplementedError):
         copy.copy(button)
     with pytest.raises(NotImplementedError):
-        copy.deepcopy(button)
+        copy.deepcopy(button)
+
+
+def test_widget_open():
+    button = Button()
+    model_id = button.model_id
+    assert model_id in widget._instances
+    spec = button.get_view_spec()
+    assert list(spec) == ["version_major", "version_minor", "model_id"]
+    assert spec["model_id"]
+    button.close()
+    assert model_id not in widget._instances
+    with pytest.raises(RuntimeError, match="Widget is closed"):
+        button.open()
+    with pytest.raises(RuntimeError, match="Widget is closed"):
+        button.get_view_spec()
+
+
+@pytest.mark.parametrize(
+    "class_name",
+    [
+        "Accordion",
+        "AppLayout",
+        "Audio",
+        "BoundedFloatText",
+        "BoundedIntText",
+        "Box",
+        "Button",
+        "ButtonStyle",
+        "Checkbox",
+        "ColorPicker",
+        "ColorsInput",
+        "Combobox",
+        "Controller",
+        "CoreWidget",
+        "DOMWidget",
+        "DatePicker",
+        "DatetimePicker",
+        "Dropdown",
+        "FileUpload",
+        "FloatLogSlider",
+        "FloatProgress",
+        "FloatRangeSlider",
+        "FloatSlider",
+        "FloatText",
+        "FloatsInput",
+        "GridBox",
+        "HBox",
+        "HTML",
+        "HTMLMath",
+        "Image",
+        "IntProgress",
+        "IntRangeSlider",
+        "IntSlider",
+        "IntText",
+        "IntsInput",
+        "Label",
+        "Layout",
+        "NaiveDatetimePicker",
+        "Output",
+        "Password",
+        "Play",
+        "RadioButtons",
+        "Select",
+        "SelectMultiple",
+        "SelectionRangeSlider",
+        "SelectionSlider",
+        "SliderStyle",
+        "Stack",
+        "Style",
+        "Tab",
+        "TagsInput",
+        "Text",
+        "Textarea",
+        "TimePicker",
+        "ToggleButton",
+        "ToggleButtons",
+        "ToggleButtonsStyle",
+        "TwoByTwoLayout",
+        "VBox",
+        "Valid",
+        "ValueWidget",
+        "Video",
+        "Widget",
+    ],
+)
+@pytest.mark.parametrize("enable_weakref", [True, False])
+def test_weakreference(class_name, enable_weakref):
+    # Ensure the base instance of all widgets can be deleted / garbage collected.
+    if enable_weakref:
+        ipw.enable_weakreference()
+    cls = getattr(ipw, class_name)
+    if class_name in ['SelectionRangeSlider', 'SelectionSlider']:
+        kwgs = {"options": [1, 2, 4]}
+    else:
+        kwgs = {}
+    try:
+        w = cls(**kwgs)
+        deleted = False
+        def on_delete():
+            nonlocal deleted
+            deleted = True
+        weakref.finalize(w, on_delete)
+        # w should be the only strong ref to the widget.
+        # calling `del` should invoke its immediate deletion calling the `__del__` method.
+        if not enable_weakref:
+            w.close()
+        del w
+        gc.collect()
+        assert deleted
+    finally:
+        if enable_weakref:
+            ipw.disable_weakreference()
+
+
+@pytest.mark.parametrize("weakref_enabled", [True, False])
+def test_button_weakreference(weakref_enabled: bool):
+    try:
+        click_count = 0
+        deleted = False
+
+        def on_delete():
+            nonlocal deleted
+            deleted = True
+
+        class TestButton(Button):
+            def my_click(self, b):
+                nonlocal click_count
+                click_count += 1
+
+        b = TestButton(description="button")
+        weakref.finalize(b, on_delete)
+        b_ref = weakref.ref(b)
+        assert b in widget._instances.values()
+
+        b.on_click(b.my_click)
+        b.on_click(lambda x: setattr(x, "clicked", True))
+
+        b.click()
+        assert click_count == 1
+
+        if weakref_enabled:
+            ipw.enable_weakreference()
+            assert b in widget._instances.values(), "Instances not transferred"
+            ipw.disable_weakreference()
+            assert b in widget._instances.values(), "Instances not transferred"
+            ipw.enable_weakreference()
+            assert b in widget._instances.values(), "Instances not transferred"
+
+        b.click()
+        assert click_count == 2
+        assert getattr(b, "clicked")
+
+        del b
+        gc.collect()
+        if weakref_enabled:
+            assert deleted
+        else:
+            assert not deleted
+            assert b_ref() in widget._instances.values()
+            b_ref().close()
+            gc.collect()
+            assert deleted, "Closing should remove the last strong reference."
+
+    finally:
+        ipw.disable_weakreference()

python/ipywidgets/ipywidgets/widgets/tests/test_widget_box.py

@@ -1,33 +1,85 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 
-from unittest import TestCase
+import gc
+import weakref
 
+import pytest
 from traitlets import TraitError
 
 import ipywidgets as widgets
 
 
-class TestBox(TestCase):
+def test_box_construction():
+    box = widgets.Box()
+    assert box.get_state()["children"] == []
 
-    def test_construction(self):
-        box = widgets.Box()
-        assert box.get_state()['children'] == []
 
-    def test_construction_with_children(self):
-        html = widgets.HTML('some html')
-        slider = widgets.IntSlider()
-        box = widgets.Box([html, slider])
-        children_state = box.get_state()['children']
-        assert children_state == [
-            widgets.widget._widget_to_json(html, None),
-            widgets.widget._widget_to_json(slider, None),
-        ]
+def test_box_construction_with_children():
+    html = widgets.HTML("some html")
+    slider = widgets.IntSlider()
+    box = widgets.Box([html, slider])
+    children_state = box.get_state()["children"]
+    assert children_state == [
+        widgets.widget._widget_to_json(html, None),
+        widgets.widget._widget_to_json(slider, None),
+    ]
 
-    def test_construction_style(self):
-        box = widgets.Box(box_style='warning')
-        assert box.get_state()['box_style'] == 'warning'
 
-    def test_construction_invalid_style(self):
-        with self.assertRaises(TraitError):
-            widgets.Box(box_style='invalid')
+def test_box_construction_style():
+    box = widgets.Box(box_style="warning")
+    assert box.get_state()["box_style"] == "warning"
+
+
+def test_construction_invalid_style():
+    with pytest.raises(TraitError):
+        widgets.Box(box_style="invalid")
+
+
+def test_box_validate_mode():
+    slider = widgets.IntSlider()
+    closed_button = widgets.Button()
+    closed_button.close()
+    with pytest.raises(TraitError, match="Invalid or closed items found.*"):
+        widgets.Box(
+        children=[closed_button, slider, "Not a widget"]
+        )
+    box = widgets.Box(
+        children=[closed_button, slider, "Not a widget"],
+        validate_mode="log_error",
+    )
+    assert len (box.children) == 1, "Invalid items should be dropped."
+    assert slider in box.children
+
+    box.validate_mode = "raise"
+    with pytest.raises(TraitError):
+        box.children += ("Not a widget", closed_button)
+
+
+def test_box_gc():
+    widgets.VBox._active_widgets
+    widgets.enable_weakreference()
+    # Test Box gc collected and children lifecycle managed.
+    try:
+        deleted = False
+
+        class TestButton(widgets.Button):
+            def my_click(self, b):
+                pass
+
+        button = TestButton(description="button")
+        button.on_click(button.my_click)
+
+        b = widgets.VBox(children=[button])
+
+        def on_delete():
+            nonlocal deleted
+            deleted = True
+
+        weakref.finalize(b, on_delete)
+        del b
+        gc.collect()
+        assert deleted
+        widgets.VBox._active_widgets
+    finally:
+        widgets.disable_weakreference()