Fix Python 3.7 test

python/ipywidgets/ipywidgets/widgets/tests/utils.py

@@ -4,16 +4,22 @@
 from ipywidgets import Widget
 import ipywidgets.widgets.widget
 
-import comm
-from ipykernel.comm import Comm
+# The new comm package is not available in our Python 3.7 CI (older ipykernel version)
+try:
+    import comm
+    NEW_COMM_PACKAGE = True
+except ImportError:
+    NEW_COMM_PACKAGE = False
+
+import ipykernel.comm
 
 
 class DummyComm():
     comm_id = 'a-b-c-d'
     kernel = 'Truthy'
 
     def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
+        super().__init__()
         self.messages = []
 
     def open(self, *args, **kwargs):
@@ -40,12 +46,24 @@ def dummy_get_comm_manager(**kwargs):
 _widget_attrs = {}
 undefined = object()
 
-orig_create_comm = comm.create_comm
-orig_get_comm_manager = comm.get_comm_manager
+if NEW_COMM_PACKAGE:
+    orig_comm = ipykernel.comm.comm.BaseComm
+else:
+    orig_comm = ipykernel.comm.Comm
+orig_create_comm = None
+orig_get_comm_manager = None
+
+if NEW_COMM_PACKAGE:
+    orig_create_comm = comm.create_comm
+    orig_get_comm_manager = comm.get_comm_manager
 
 def setup_test_comm():
-    comm.create_comm = dummy_create_comm
-    comm.get_comm_manager = dummy_get_comm_manager
+    if NEW_COMM_PACKAGE:
+        comm.create_comm = dummy_create_comm
+        comm.get_comm_manager = dummy_get_comm_manager
+        ipykernel.comm.comm.BaseComm = DummyComm
+    else:
+        ipykernel.comm.Comm = DummyComm
     Widget.comm.klass = DummyComm
     ipywidgets.widgets.widget.Comm = DummyComm
     _widget_attrs['_repr_mimebundle_'] = Widget._repr_mimebundle_
@@ -54,10 +72,14 @@ def raise_not_implemented(*args, **kwargs):
     Widget._repr_mimebundle_ = raise_not_implemented
 
 def teardown_test_comm():
-    comm.create_comm = orig_create_comm
-    comm.get_comm_manager = orig_get_comm_manager
-    Widget.comm.klass = Comm
-    ipywidgets.widgets.widget.Comm = Comm
+    if NEW_COMM_PACKAGE:
+        comm.create_comm = orig_create_comm
+        comm.get_comm_manager = orig_get_comm_manager
+        ipykernel.comm.comm.BaseComm = orig_comm
+    else:
+        ipykernel.comm.Comm = orig_comm
+    Widget.comm.klass = orig_comm
+    ipywidgets.widgets.widget.Comm = orig_comm
     for attr, value in _widget_attrs.items():
         if value is undefined:
             delattr(Widget, attr)

python/ipywidgets/ipywidgets/widgets/widget.py

@@ -11,7 +11,7 @@
 from collections.abc import Iterable
 from IPython import get_ipython
 from traitlets import (
-    Any, HasTraits, Unicode, Dict, Instance, List, Int, Set, Bytes, observe, default, Container,
+    HasTraits, Unicode, Dict, Instance, List, Int, Set, Bytes, observe, default, Container,
     Undefined)
 from json import loads as jsonloads, dumps as jsondumps
 
@@ -479,7 +479,7 @@ def get_view_spec(self):
 
     _view_count = Int(None, allow_none=True,
         help="EXPERIMENTAL: The number of views of the model displayed in the frontend. This attribute is experimental and may change or be removed in the future. None signifies that views will not be tracked. Set this to 0 to start tracking view creation/deletion.").tag(sync=True)
-    comm = Any(None, allow_none=True)
+    comm = Instance(object, allow_none=True)
 
     keys = List(help="The traits which are synced.")
 
@@ -693,7 +693,7 @@ def notify_change(self, change):
         # Send the state to the frontend before the user-registered callbacks
         # are called.
         name = change['name']
-        if self.comm is not None:
+        if self.comm is not None and (self.comm.kernel is not None if hasattr(self.comm, "kernel") else True):
             # Make sure this isn't information that the front-end just sent us.
             if name in self.keys and self._should_send_property(name, getattr(self, name)):
                 # Send new state to front-end
@@ -821,7 +821,7 @@ def _repr_mimebundle_(self, **kwargs):
 
     def _send(self, msg, buffers=None):
         """Sends a message to the model in the front-end."""
-        if self.comm is not None:
+        if self.comm is not None and (self.comm.kernel is not None if hasattr(self.comm, "kernel") else True):
             self.comm.send(data=msg, buffers=buffers)
 
     def _repr_keys(self):