fix: allow use of comm package (jupyter-widgets#3533)

* Move comm package

* Fix wrongly written test

This test was supposed to fail, as setting the bottom_left value will
trigger a ipywidgets.Layout.send_state on `child.layout.grid_area = position`
(ipywidgets.widgets.widget_template.py L419) and on
`self.layout.grid_template_areas = grid_template_areas_css`
(ipywidgets.widgets.widget_template.py L448)

* Fix Python 3.7 test

Co-authored-by: Maarten Breddels <maartenbreddels@gmail.com>
(cherry picked from commit 785d159)

ipywidgets/__init__.py

@@ -20,25 +20,36 @@
 
 import os
 
+from traitlets import link, dlink
 from IPython import get_ipython
+
+try:
+    from comm import get_comm_manager
+except ImportError:
+    def get_comm_manager():
+        ip = get_ipython()
+
+        if ip is not None and ip.kernel is not None:
+            return get_ipython().kernel.comm_manager
+
 from ._version import version_info, __version__, __protocol_version__, __jupyter_widgets_controls_version__, __jupyter_widgets_base_version__
 from .widgets import *
-from traitlets import link, dlink
+
 
 
 def load_ipython_extension(ip):
     """Set up IPython to work with widgets"""
     if not hasattr(ip, 'kernel'):
         return
-    register_comm_target(ip.kernel)
+    register_comm_target()
 
 
 def register_comm_target(kernel=None):
     """Register the jupyter.widget comm target"""
-    if kernel is None:
-        kernel = get_ipython().kernel
-    kernel.comm_manager.register_target('jupyter.widget', Widget.handle_comm_opened)
-    kernel.comm_manager.register_target('jupyter.widget.control', Widget.handle_control_comm_opened)
+    comm_manager = get_comm_manager()
+
+    comm_manager.register_target('jupyter.widget', Widget.handle_comm_opened)
+    comm_manager.register_target('jupyter.widget.control', Widget.handle_control_comm_opened)
 
 # deprecated alias
 handle_kernel = register_comm_target
@@ -48,6 +59,6 @@ def _handle_ipython():
     ip = get_ipython()
     if ip is None:
         return
-    load_ipython_extension(ip)
+    register_comm_target()
 
 _handle_ipython()

ipywidgets/tests/test_embed.py

@@ -7,7 +7,10 @@
 
 import traitlets
 
-from ..widgets import IntSlider, IntText, Text, Widget, jslink, HBox, widget_serialization
+# This has a byproduct of setting up the comms
+import ipykernel.ipkernel
+
+from ..widgets import IntSlider, IntText, Text, Widget, jslink, HBox, widget_serialization, widget
 from ..embed import embed_data, embed_snippet, embed_minimal_html, dependency_state
 
 try:

ipywidgets/widgets/tests/test_interaction.py

@@ -734,4 +734,3 @@ def test_state_schema():
     with open(os.path.join(os.path.dirname(os.path.realpath(__file__)), '../../', 'state.schema.json')) as f:
         schema = json.load(f)
     jsonschema.validate(state, schema)
-

ipywidgets/widgets/tests/test_widget_templates.py

@@ -233,7 +233,7 @@ def test_update_dynamically(self, send_state): #pylint: disable=no-self-use
         assert box.layout.grid_template_areas == ('"top-left top-right"\n' +
                                                   '"bottom-left bottom-right"')
         # check whether frontend was informed
-        send_state.assert_called_once_with(key="grid_template_areas")
+        send_state.assert_called_with(key="grid_template_areas")
 
         box = widgets.TwoByTwoLayout(top_left=button1, top_right=button3,
                                      bottom_left=None, bottom_right=button4)
@@ -244,7 +244,7 @@ def test_update_dynamically(self, send_state): #pylint: disable=no-self-use
         box.merge = False
         assert box.layout.grid_template_areas == ('"top-left top-right"\n' +
                                                   '"bottom-left bottom-right"')
-        send_state.assert_called_once_with(key="grid_template_areas")
+        send_state.assert_called_with(key="grid_template_areas")
 
 
 class TestAppLayout(TestCase):

ipywidgets/widgets/tests/utils.py

@@ -1,31 +1,69 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 
-from ipykernel.comm import Comm
 from ipywidgets import Widget
 import ipywidgets.widgets.widget
 
-class DummyComm(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(DummyComm, self).__init__(*args, **kwargs)
+        super().__init__()
         self.messages = []
 
     def open(self, *args, **kwargs):
         pass
 
+    def on_msg(self, *args, **kwargs):
+        pass
+
     def send(self, *args, **kwargs):
         self.messages.append((args, kwargs))
 
     def close(self, *args, **kwargs):
         pass
 
+
+def dummy_create_comm(**kwargs):
+    return DummyComm()
+
+
+def dummy_get_comm_manager(**kwargs):
+    return {}
+
+
 _widget_attrs = {}
 undefined = object()
 
+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():
+    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['_ipython_display_'] = Widget._ipython_display_
@@ -34,8 +72,14 @@ def raise_not_implemented(*args, **kwargs):
     Widget._ipython_display_ = raise_not_implemented
 
 def teardown_test_comm():
-    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)

ipywidgets/widgets/widget.py

@@ -18,7 +18,7 @@
 from IPython.core.getipython import get_ipython
 from ipykernel.comm import Comm
 from traitlets import (
-    HasTraits, Unicode, Dict, Instance, List, Int, Set, Bytes, observe, default, Container,
+    Any, HasTraits, Unicode, Dict, Instance, List, Int, Set, Bytes, observe, default, Container,
     Undefined)
 from ipython_genutils.py3compat import string_types, PY3
 from IPython.display import display
@@ -454,7 +454,7 @@ 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 = Instance('ipykernel.comm.Comm', allow_none=True)
+    comm = Any(allow_none=True)
 
     keys = List(help="The traits which are synced.")
 
@@ -500,7 +500,15 @@ def open(self):
             if self._model_id is not None:
                 args['comm_id'] = self._model_id
 
-            self.comm = Comm(**args)
+            try:
+                from comm import create_comm
+            except ImportError:
+                def create_comm(**kwargs):
+                    from ipykernel.comm import Comm
+
+                    return Comm(**kwargs)
+
+            self.comm = create_comm(**args)
 
     @observe('comm')
     def _comm_changed(self, change):
@@ -678,7 +686,7 @@ 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 and self.comm.kernel is not None:
+        if self.comm is not None and getattr(self.comm, 'kernel', True) is not None:
             # 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
@@ -813,7 +821,7 @@ def _ipython_display_(self, **kwargs):
 
     def _send(self, msg, buffers=None):
         """Sends a message to the model in the front-end."""
-        if self.comm is not None and self.comm.kernel 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):

ipywidgets/widgets/widget_output.py

@@ -31,7 +31,7 @@ class Output(DOMWidget):
     context will be captured and displayed in the widget instead of the standard output
     area.
 
-    You can also use the .capture() method to decorate a function or a method. Any output 
+    You can also use the .capture() method to decorate a function or a method. Any output
     produced by the function will then go to the output widget. This is useful for
     debugging widget callbacks, for example.
 

setup.py

@@ -110,7 +110,6 @@
 
 setuptools_args = {}
 install_requires = setuptools_args['install_requires'] = [
-    'ipykernel>=4.5.1',
     'ipython_genutils~=0.2.0',
     'traitlets>=4.3.1',
     # TODO: Dynamically add this dependency
@@ -125,7 +124,7 @@
     ':python_version>="3.3"': ['ipython>=4.0.0'],
     ':python_version>="3.6"': ['jupyterlab_widgets>=1.0.0,<3'],
     'test:python_version=="2.7"': ['mock'],
-    'test': ['pytest>=3.6.0', 'pytest-cov'],
+    'test': ['pytest>=3.6.0', 'pytest-cov', 'ipykernel'],
 }
 
 if 'setuptools' in sys.modules: