Don't pass None kernels to logging configurable in Comm (#1061)

Co-authored-by: Steven Silvester <steven.silvester@ieee.org>
fixes undefined

ipykernel/comm/comm.py

@@ -70,13 +70,16 @@ def _default_comm_id(self):
 
     def __init__(self, target_name='', data=None, metadata=None, buffers=None, **kwargs):
         # Handle differing arguments between base classes.
+        had_kernel = 'kernel' in kwargs
         kernel = kwargs.pop('kernel', None)
         if target_name:
             kwargs['target_name'] = target_name
         BaseComm.__init__(
             self, data=data, metadata=metadata, buffers=buffers, **kwargs
         )  # type:ignore[call-arg]
-        kwargs['kernel'] = kernel
+        # only re-add kernel if explicitly provided
+        if had_kernel:
+            kwargs['kernel'] = kernel
         traitlets.config.LoggingConfigurable.__init__(self, **kwargs)
 
 

ipykernel/tests/test_comm.py

@@ -2,15 +2,18 @@
 
 from ipykernel.comm import Comm, CommManager
 from ipykernel.ipkernel import IPythonKernel
+from ipykernel.kernelbase import Kernel
 
 
-def test_comm(kernel):
+def test_comm(kernel: Kernel) -> None:
     manager = CommManager(kernel=kernel)
-    kernel.comm_manager = manager
+    kernel.comm_manager = manager  # type:ignore
 
     c = Comm(kernel=kernel, target_name="bar")
     msgs = []
 
+    assert kernel is c.kernel  # type:ignore
+
     def on_close(msg):
         msgs.append(msg)
 
@@ -28,7 +31,7 @@ def on_message(msg):
     assert c.target_name == "bar"
 
 
-def test_comm_manager(kernel):
+def test_comm_manager(kernel: Kernel) -> None:
     manager = CommManager(kernel=kernel)
     msgs = []
 
@@ -48,14 +51,19 @@ def on_msg(msg):
     manager.register_target("foo", foo)
     manager.register_target("fizz", fizz)
 
-    kernel.comm_manager = manager
+    kernel.comm_manager = manager  # type:ignore
     with unittest.mock.patch.object(Comm, "publish_msg") as publish_msg:
         comm = Comm()
         comm.on_msg(on_msg)
         comm.on_close(on_close)
         manager.register_comm(comm)
         assert publish_msg.call_count == 1
 
+    # make sure that when we don't pass a kernel, the 'default' kernel is taken
+    Kernel._instance = kernel  # type:ignore
+    assert comm.kernel is kernel  # type:ignore
+    Kernel.clear_instance()
+
     assert manager.get_comm(comm.comm_id) == comm
     assert manager.get_comm('foo') is None