Make comm manager (mostly) independent of InteractiveShell

This makes it possible to use comms from wrapper kernels, without
instantiating the full IPython shell machinery.

The one remaining place where we need a reference to shell is to fire
pre_execute and post_execute hooks (which are needed to get mpl figures
right). This is a pure IPythonism, that it should be safe to ignore if
shell is not set.

IPython/kernel/comm/comm.py

@@ -14,18 +14,17 b' from IPython.utils.traitlets import Instance, Unicode, Bytes, Bool, Dict, Any'
 
 class Comm(LoggingConfigurable):
     
-    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC')
-    def _shell_default(self):
-        return get_ipython()
+    # If this is instantiated by a non-IPython kernel, shell will be None
+    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC',
+                     allow_none=True)
+    kernel = Instance('IPython.kernel.zmq.kernelbase.Kernel')
     
     iopub_socket = Any()
     def _iopub_socket_default(self):
-        return self.shell.kernel.iopub_socket
+        return self.kernel.iopub_socket
     session = Instance('IPython.kernel.zmq.session.Session')
     def _session_default(self):
-        if self.shell is None or not hasattr(self.shell, 'kernel'):
-            return
-        return self.shell.kernel.session
+        return self.kernel.session
     
     target_name = Unicode('comm')
     
@@ -63,7 +62,7 b' class Comm(LoggingConfigurable):'
             self.session.send(self.iopub_socket, msg_type,
                 content,
                 metadata=json_clean(metadata),
-                parent=self.shell.get_parent(),
+                parent=self.kernel._parent_header,
                 ident=self.topic,
             )
     
@@ -132,8 +131,10 b' class Comm(LoggingConfigurable):'
         """Handle a comm_msg message"""
         self.log.debug("handle_msg[%s](%s)", self.comm_id, msg)
         if self._msg_callback:
+            if self.shell:
             self.shell.events.trigger('pre_execute')
             self._msg_callback(msg)
+            if self.shell:
             self.shell.events.trigger('post_execute')
 
 

IPython/kernel/comm/manager.py

@@ -28,17 +28,17 b' def lazy_keys(dikt):'
 class CommManager(LoggingConfigurable):
     """Manager for Comms in the Kernel"""
     
-    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC')
-    def _shell_default(self):
-        return get_ipython()
+    # If this is instantiated by a non-IPython kernel, shell will be None
+    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC',
+                     allow_none=True)
+    kernel = Instance('IPython.kernel.zmq.kernelbase.Kernel')
+
     iopub_socket = Any()
     def _iopub_socket_default(self):
-        return self.shell.kernel.iopub_socket
+        return self.kernel.iopub_socket
     session = Instance('IPython.kernel.zmq.session.Session')
     def _session_default(self):
-        if self.shell is None:
-            return
-        return self.shell.kernel.session
+        return self.kernel.session
     
     comms = Dict()
     targets = Dict()
@@ -68,6 +68,7 b' class CommManager(LoggingConfigurable):'
         """Register a new comm"""
         comm_id = comm.comm_id
         comm.shell = self.shell
+        comm.kernel = self.kernel
         comm.iopub_socket = self.iopub_socket
         self.comms[comm_id] = comm
         return comm_id
@@ -102,6 +103,7 b' class CommManager(LoggingConfigurable):'
         f = self.targets.get(target_name, None)
         comm = Comm(comm_id=comm_id,
                     shell=self.shell,
+                    kernel=self.kernel,
                     iopub_socket=self.iopub_socket,
                     primary=False,
         )

IPython/kernel/zmq/zmqshell.py

@@ -565,7 +565,8 b' class ZMQInteractiveShell(InteractiveShell):'
         self.magics_manager.register_alias('ed', 'edit')
     
     def init_comms(self):
-        self.comm_manager = CommManager(shell=self, parent=self)
+        self.comm_manager = CommManager(shell=self, parent=self, 
+                                        kernel=self.kernel)
         self.configurables.append(self.comm_manager)