fix: make .widget and .widget_types deprecated

In jupyter-widgets#3122 we renamed .widget and .widget_types to ._active_widgets
and ._widget_types. That breaks code, and we did not have a deprecation
period.
This PR makes the dict and registry non-members of the Widget class
and puts in a backwards compatible way the deprecated these members.

python/ipywidgets/ipywidgets/embed.py

@@ -12,6 +12,7 @@
 
 import json
 import re
+import ipywidgets.widgets.widget
 from .widgets import Widget, DOMWidget
 from .widgets.widget_link import Link
 from .widgets.docutils import doc_subst
@@ -129,7 +130,7 @@ def _get_recursive_state(widget, store=None, drop_defaults=False):
 
 def add_resolved_links(store, drop_defaults):
     """Adds the state of any link models between two models in store"""
-    for widget_id, widget in Widget._active_widgets.items(): # go over all widgets
+    for widget_id, widget in ipywidgets.widgets.widget.instances.items(): # go over all widgets
         if isinstance(widget, Link) and widget_id not in store:
             if widget.source[0].model_id in store and widget.target[0].model_id in store:
                 store[widget.model_id] = widget._get_embed_state(drop_defaults=drop_defaults)
@@ -207,7 +208,7 @@ def embed_data(views, drop_defaults=True, state=None):
         view_specs: a list of widget view specs
     """
     if views is None:
-        views = [w for w in Widget._active_widgets.values() if isinstance(w, DOMWidget)]
+        views = [w for w in ipywidgets.widgets.widget.instances.values() if isinstance(w, DOMWidget)]
     else:
         try:
             views[0]

python/ipywidgets/ipywidgets/tests/test_embed.py

@@ -9,6 +9,7 @@
 
 import traitlets
 
+import ipywidgets.widgets.widget
 from ..widgets import IntSlider, IntText, Text, Widget, jslink, HBox, widget_serialization
 from ..embed import embed_data, embed_snippet, embed_minimal_html, dependency_state
 
@@ -29,7 +30,7 @@ class CaseWidget(Widget):
 class TestEmbed:
 
     def teardown(self):
-        for w in tuple(Widget._active_widgets.values()):
+        for w in tuple(ipywidgets.widgets.widget.instances.values()):
             w.close()
 
     def test_embed_data_simple(self):

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

@@ -7,6 +7,7 @@
 from IPython.display import display
 from IPython.utils.capture import capture_output
 
+from .. import widget
 from ..widget import Widget
 from ..widget_button import Button
 
@@ -49,9 +50,22 @@ def test_close_all():
     # create a couple of widgets
     widgets = [Button() for i in range(10)]
 
-    assert len(Widget._active_widgets) > 0, "expect active widgets"
+    assert len(widget.instances) > 0, "expect active widgets"
 
     # close all the widgets
     Widget.close_all()
 
-    assert len(Widget._active_widgets) == 0, "active widgets should be cleared"
+    assert len(widget.instances) == 0, "active widgets should be cleared"
+
+
+def test_compatibility():
+    button = Button()
+    assert button in widget.Widget.widgets.values()
+    assert widget.instances is widget.Widget.widgets
+    assert widget.instances is widget.Widget._active_widgets
+    Widget.close_all()
+    assert not widget.Widget.widgets
+    assert not widget.Widget._active_widgets
+
+    assert widget.Widget.widget_types is widget.registry
+    assert widget.Widget._widget_types is widget.registry

python/ipywidgets/ipywidgets/widgets/widget.py

@@ -6,8 +6,10 @@
 in the Jupyter notebook front-end.
 """
 import os
+import typing
 from contextlib import contextmanager
 from collections.abc import Iterable
+import warnings
 from IPython import get_ipython
 from ipykernel.comm import Comm
 from traitlets import (
@@ -34,6 +36,9 @@ def envset(name, default):
 PROTOCOL_VERSION_MAJOR = __protocol_version__.split('.')[0]
 CONTROL_PROTOCOL_VERSION_MAJOR = __control_protocol_version__.split('.')[0]
 JUPYTER_WIDGETS_ECHO = envset('JUPYTER_WIDGETS_ECHO', default=True)
+# we keep a strong reference for every widget created, for a discussion on using weak references see:
+#  https://github.com/jupyter-widgets/ipywidgets/issues/1345
+instances : typing.MutableMapping[str, "Widget"] = {}
 
 def _widget_to_json(x, obj):
     if isinstance(x, dict):
@@ -50,8 +55,8 @@ def _json_to_widget(x, obj):
         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 Widget._active_widgets:
-        return Widget._active_widgets[x[10:]]
+    elif isinstance(x, str) and x.startswith('IPY_MODEL_') and x[10:] in instances:
+        return instances[x[10:]]
     else:
         return x
 
@@ -259,10 +264,16 @@ def items(self):
                             for view_name, widget in sorted(vn.items()):
                                     yield (model_module, model_version, model_name, view_module, view_version, view_name), widget
 
+
+
+# a registry of widgets by module, version, and name so we can create a Python model from widgets
+# that are constructed from the frontend.
+registry = WidgetRegistry()
+
 def register(widget):
     """A decorator registering a widget class in the widget registry."""
     w = widget.class_traits()
-    Widget._widget_types.register(w['_model_module'].default_value,
+    registry.register(w['_model_module'].default_value,
                                  w['_model_module_version'].default_value,
                                  w['_model_name'].default_value,
                                  w['_view_module'].default_value,
@@ -272,22 +283,46 @@ def register(widget):
     return widget
 
 
+class _staticproperty(object):
+    def __init__(self, fget):
+        self.fget = fget
+
+    def __get__(self, owner_self, owner_cls):
+        assert owner_self is None
+        return self.fget()
+
+
+
 class Widget(LoggingHasTraits):
     #-------------------------------------------------------------------------
     # Class attributes
     #-------------------------------------------------------------------------
     _widget_construction_callback = None
     _control_comm = None
 
-    # _active_widgets is a dictionary of all active widget objects
-    _active_widgets = {}
+    @_staticproperty
+    def widgets():
+        warnings.warn("Widget.widgets is deprecated, use ipywidgets.widgets.widget.instances", DeprecationWarning)
+        return instances
+
+    @_staticproperty
+    def _active_widgets():
+        warnings.warn("Widget._active_widgets is deprecated, use ipywidgets.widgets.widget.instances", DeprecationWarning)
+        return instances
+
+    @_staticproperty
+    def _widget_types():
+        warnings.warn("Widget._widget_types is deprecated, use ipywidgets.widgets.widget.register", DeprecationWarning)
+        return registry
 
-    # _widget_types is a registry of widgets by module, version, and name:
-    _widget_types = WidgetRegistry()
+    @_staticproperty
+    def widget_types():
+        warnings.warn("Widget.widget_types is deprecated, use ipywidgets.widgets.widget.register", DeprecationWarning)
+        return registry
 
     @classmethod
     def close_all(cls):
-        for widget in list(cls._active_widgets.values()):
+        for widget in list(instances.values()):
             widget.close()
 
     @staticmethod
@@ -329,7 +364,7 @@ def _handle_control_comm_msg(cls, msg):
         if method == 'request_states':
             # Send back the full widgets state
             cls.get_manager_state()
-            widgets = cls._active_widgets.values()
+            widgets = instances.values()
             full_state = {}
             drop_defaults = False
             for widget in widgets:
@@ -359,7 +394,7 @@ def handle_comm_opened(comm, msg):
         state = data['state']
 
         # Find the widget class to instantiate in the registered widgets
-        widget_class = Widget._widget_types.get(state['_model_module'],
+        widget_class = register.get(state['_model_module'],
                                                state['_model_module_version'],
                                                state['_model_name'],
                                                state['_view_module'],
@@ -380,7 +415,7 @@ def get_manager_state(drop_defaults=False, widgets=None):
         """
         state = {}
         if widgets is None:
-            widgets = Widget._active_widgets.values()
+            widgets = instances.values()
         for widget in widgets:
             state[widget.model_id] = widget._get_embed_state(drop_defaults=drop_defaults)
         return {'version_major': 2, 'version_minor': 0, 'state': state}
@@ -476,7 +511,7 @@ def _comm_changed(self, change):
         self._model_id = self.model_id
 
         self.comm.on_msg(self._handle_msg)
-        Widget._active_widgets[self.model_id] = self
+        instances[self.model_id] = self
 
     @property
     def model_id(self):
@@ -496,7 +531,7 @@ def close(self):
         When the comm is closed, all of the widget views are automatically
         removed from the front-end."""
         if self.comm is not None:
-            Widget._active_widgets.pop(self.model_id, None)
+            instances.pop(self.model_id, None)
             self.comm.close()
             self.comm = None
             self._repr_mimebundle_ = None