Enable widget instanciation from front-end.

IPython/html/static/widgets/js/manager.js

@@ -1,224 +1,259 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     "underscore",
     "backbone",
     "jquery",
     "base/js/namespace"
 ], function (_, Backbone, $, IPython) {
     "use strict";
     //--------------------------------------------------------------------
     // WidgetManager class
     //--------------------------------------------------------------------
     var WidgetManager = function (comm_manager, notebook) {
         // Public constructor
         WidgetManager._managers.push(this);
 
         // Attach a comm manager to the 
         this.keyboard_manager = notebook.keyboard_manager;
         this.notebook = notebook;
         this.comm_manager = comm_manager;
         this._models = {}; /* Dictionary of model ids and model instances */
 
         // Register with the comm manager.
         this.comm_manager.register_target('ipython.widget', $.proxy(this._handle_comm_open, this));
     };
 
     //--------------------------------------------------------------------
     // Class level
     //--------------------------------------------------------------------
     WidgetManager._model_types = {}; /* Dictionary of model type names (target_name) and model types. */
     WidgetManager._view_types = {}; /* Dictionary of view names and view types. */
     WidgetManager._managers = []; /* List of widget managers */
 
     WidgetManager.register_widget_model = function (model_name, model_type) {
         // Registers a widget model by name.
         WidgetManager._model_types[model_name] = model_type;
     };
 
     WidgetManager.register_widget_view = function (view_name, view_type) {
         // Registers a widget view by name.
         WidgetManager._view_types[view_name] = view_type;
     };
 
     //--------------------------------------------------------------------
     // Instance level
     //--------------------------------------------------------------------
     WidgetManager.prototype.display_view = function(msg, model) {
         // Displays a view for a particular model.
         var cell = this.get_msg_cell(msg.parent_header.msg_id);
         if (cell === null) {
             console.log("Could not determine where the display" + 
                 " message was from.  Widget will not be displayed");
         } else {
             var that = this;
             this.create_view(model, {cell: cell, callback: function(view) {
                 that._handle_display_view(view);
                 if (cell.widget_subarea) {
                     cell.widget_subarea.append(view.$el);
                 }
                 view.trigger('displayed');
             }});
         }
     };
 
     WidgetManager.prototype._handle_display_view = function (view) {
         // Have the IPython keyboard manager disable its event
         // handling so the widget can capture keyboard input.
         // Note, this is only done on the outer most widgets.
         if (this.keyboard_manager) {
             this.keyboard_manager.register_events(view.$el);
         
         if (view.additional_elements) {
             for (var i = 0; i < view.additional_elements.length; i++) {
                     this.keyboard_manager.register_events(view.additional_elements[i]);
             }
         } 
         }
     };
     
 
     WidgetManager.prototype.create_view = function(model, options) {
         // Creates a view for a particular model.
         
         var view_name = model.get('_view_name');
         var view_mod = model.get('_view_module');
         var errback = options.errback || function(err) {console.log(err);};
 
         var instantiate_view = function(ViewType) {
             if (ViewType) {
                 // If a view is passed into the method, use that view's cell as
                 // the cell for the view that is created.
                 options = options || {};
                 if (options.parent !== undefined) {
                     options.cell = options.parent.options.cell;
                 }
 
                 // Create and render the view...
                 var parameters = {model: model, options: options};
                 var view = new ViewType(parameters);
                 view.render();
                 model.on('destroy', view.remove, view);
                 options.callback(view);
             } else {
                 errback({unknown_view: true, view_name: view_name,
                          view_module: view_mod});
             }
         };
 
         if (view_mod) {
             require([view_mod], function(module) {
                 instantiate_view(module[view_name]);
             }, errback);
         } else {
             instantiate_view(WidgetManager._view_types[view_name]);
         }
     };
 
     WidgetManager.prototype.get_msg_cell = function (msg_id) {
         var cell = null;
         // First, check to see if the msg was triggered by cell execution.
         if (this.notebook) {
             cell = this.notebook.get_msg_cell(msg_id);
         }
         if (cell !== null) {
             return cell;
         }
         // Second, check to see if a get_cell callback was defined
         // for the message.  get_cell callbacks are registered for
         // widget messages, so this block is actually checking to see if the
         // message was triggered by a widget.
         var kernel = this.comm_manager.kernel;
         if (kernel) {
             var callbacks = kernel.get_callbacks_for_msg(msg_id);
             if (callbacks && callbacks.iopub &&
                 callbacks.iopub.get_cell !== undefined) {
                 return callbacks.iopub.get_cell();
             }
         }
         
         // Not triggered by a cell or widget (no get_cell callback 
         // exists).
         return null;
     };
 
     WidgetManager.prototype.callbacks = function (view) {
         // callback handlers specific a view
         var callbacks = {};
         if (view && view.options.cell) {
 
             // Try to get output handlers
             var cell = view.options.cell;
             var handle_output = null;
             var handle_clear_output = null;
             if (cell.output_area) {
                 handle_output = $.proxy(cell.output_area.handle_output, cell.output_area);
                 handle_clear_output = $.proxy(cell.output_area.handle_clear_output, cell.output_area);
             }
 
             // Create callback dict using what is known
             var that = this;
             callbacks = {
                 iopub : {
                     output : handle_output,
                     clear_output : handle_clear_output,
 
                     // Special function only registered by widget messages.
                     // Allows us to get the cell for a message so we know
                     // where to add widgets if the code requires it.
                     get_cell : function () {
                         return cell;
                     },
                 },
             };
         }
         return callbacks;
     };
 
     WidgetManager.prototype.get_model = function (model_id) {
         // Look-up a model instance by its id.
         var model = this._models[model_id];
         if (model !== undefined && model.id == model_id) {
             return model;
         }
         return null;
     };
 
     WidgetManager.prototype._handle_comm_open = function (comm, msg) {
         // Handle when a comm is opened.
+        return this.create_model({model_name: msg.content.data.target_name, comm: comm});
+    };
+
+    WidgetManager.prototype.create_model = function (model_name, target_name) {
+        // Create and return a new widget model.
+        //
+        // Parameters
+        // ----------
+        // model_name: string
+        //      Target name of the widget model to create.
+        // target_name: string
+        //      Target name of the widget in the back-end.
+        return this._create_model({model_name: model_name, target_name: target_name});
+    };
+
+    WidgetManager.prototype._create_model = function (options) {
+        // Create and return a new widget model.
+        //
+        // Parameters
+        // ----------
+        // options: dictionary
+        //  Dictionary of options with the following contents:
+        //      model_name: string
+        //          Target name of the widget model to create.
+        //      target_name: (optional) string
+        //          Target name of the widget in the back-end.
+        //      comm: (optional) Comm
+
+        // Create a comm if it wasn't provided.
+        var comm = options.comm;
+        if (!comm) {
+            comm = this.comm_manager.new_comm('ipython.widget', {'target_name': options.target_name});
+        }
+
+        // Create and return a new model that is connected to the comm.
         var that = this;
         
         var instantiate_model = function(ModelType) {
             var model_id = comm.comm_id;
             var widget_model = new ModelType(that, model_id, comm);
-            widget_model.on('comm:close', function () {
+            widget_model.on('comm:close', function () {sss
               delete that._models[model_id];
             });
             that._models[model_id] = widget_model;
         };
         
         var widget_type_name = msg.content.data.model_name;
         var widget_module = msg.content.data.model_module;
 
         if (widget_module) {
             // Load the module containing the widget model
             require([widget_module], function(mod) {
                 if (mod[widget_type_name]) {
                     instantiate_model(mod[widget_type_name]);
                 } else {
                     console.log("Error creating widget model: " + widget_type_name
                             + " not found in " + widget_module);
                 }
             }, function(err) { console.log(err); });
         } else {
             // No module specified, load from the global models registry
             instantiate_model(WidgetManager._model_types[widget_type_name]);
         }
     };
 
     // Backwards compatability.
     IPython.WidgetManager = WidgetManager;
 
     return {'WidgetManager': WidgetManager};
 });

IPython/html/widgets/widget.py

@@ -1,454 +1,469 b''
 """Base Widget class.  Allows user to create widgets in the back-end that render
 in the IPython notebook front-end.
 """
 #-----------------------------------------------------------------------------
 # Copyright (c) 2013, the IPython Development Team.
 #
 # Distributed under the terms of the Modified BSD License.
 #
 # The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 from contextlib import contextmanager
 import collections
 
 from IPython.core.getipython import get_ipython
 from IPython.kernel.comm import Comm
 from IPython.config import LoggingConfigurable
+from IPython.utils.importstring import import_item
 from IPython.utils.traitlets import Unicode, Dict, Instance, Bool, List, \
     CaselessStrEnum, Tuple, CUnicode, Int, Set
 from IPython.utils.py3compat import string_types
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 class CallbackDispatcher(LoggingConfigurable):
     """A structure for registering and running callbacks"""
     callbacks = List()
     
     def __call__(self, *args, **kwargs):
         """Call all of the registered callbacks."""
         value = None
         for callback in self.callbacks:
             try:
                 local_value = callback(*args, **kwargs)
             except Exception as e:
                 ip = get_ipython()
                 if ip is None:
                     self.log.warn("Exception in callback %s: %s", callback, e, exc_info=True)
                 else:
                     ip.showtraceback()
             else:
                 value = local_value if local_value is not None else value
         return value
 
     def register_callback(self, callback, remove=False):
         """(Un)Register a callback
 
         Parameters
         ----------
         callback: method handle
             Method to be registered or unregistered.
         remove=False: bool
             Whether to unregister the callback."""
         
         # (Un)Register the callback.
         if remove and callback in self.callbacks:
             self.callbacks.remove(callback)
         elif not remove and callback not in self.callbacks:
             self.callbacks.append(callback)
 
 def _show_traceback(method):
     """decorator for showing tracebacks in IPython"""
     def m(self, *args, **kwargs):
         try:
             return(method(self, *args, **kwargs))
         except Exception as e:
             ip = get_ipython()
             if ip is None:
                 self.log.warn("Exception in widget method %s: %s", method, e, exc_info=True)
             else:
                 ip.showtraceback()
     return m
 
 class Widget(LoggingConfigurable):
     #-------------------------------------------------------------------------
     # Class attributes
     #-------------------------------------------------------------------------
     _widget_construction_callback = None
     widgets = {}
 
     @staticmethod
     def on_widget_constructed(callback):
         """Registers a callback to be called when a widget is constructed.
 
         The callback must have the following signature:
         callback(widget)"""
         Widget._widget_construction_callback = callback
 
     @staticmethod
     def _call_widget_constructed(widget):
         """Static method, called when a widget is constructed."""
         if Widget._widget_construction_callback is not None and callable(Widget._widget_construction_callback):
             Widget._widget_construction_callback(widget)
 
+    @staticmethod
+    def handle_comm_opened(comm, msg):
+        """Static method, called when a widget is constructed."""
+        target_name = msg['content']['data']['target_name']
+        widget_class = import_item(target_name)
+        widget = widget_class(open_comm=False)
+        widget.set_comm(comm)
+
+
     #-------------------------------------------------------------------------
     # Traits
     #-------------------------------------------------------------------------
     _model_module = Unicode(None, allow_none=True, help="""A requirejs module name
         in which to find _model_name. If empty, look in the global registry.""")
     _model_name = Unicode('WidgetModel', help="""Name of the backbone model 
         registered in the front-end to create and sync this widget with.""")
     _view_module = Unicode(help="""A requirejs module in which to find _view_name.
         If empty, look in the global registry.""", sync=True)
     _view_name = Unicode(None, allow_none=True, help="""Default view registered in the front-end
         to use to represent the widget.""", sync=True)
     comm = Instance('IPython.kernel.comm.Comm')
     
     msg_throttle = Int(3, sync=True, help="""Maximum number of msgs the 
         front-end can send before receiving an idle msg from the back-end.""")
     
     version = Int(0, sync=True, help="""Widget's version""")
     keys = List()
     def _keys_default(self):
         return [name for name in self.traits(sync=True)]
     
     _property_lock = Tuple((None, None))
     _send_state_lock = Int(0)
     _states_to_send = Set(allow_none=False)
     _display_callbacks = Instance(CallbackDispatcher, ())
     _msg_callbacks = Instance(CallbackDispatcher, ())
     
     #-------------------------------------------------------------------------
     # (Con/de)structor
     #-------------------------------------------------------------------------
-    def __init__(self, **kwargs):
+    def __init__(self, open_comm=True, **kwargs):
         """Public constructor"""
         self._model_id = kwargs.pop('model_id', None)
         super(Widget, self).__init__(**kwargs)
 
         Widget._call_widget_constructed(self)
+        if open_comm:
         self.open()
 
     def __del__(self):
         """Object disposal"""
         self.close()
 
     #-------------------------------------------------------------------------
     # Properties
     #-------------------------------------------------------------------------
 
     def open(self):
         """Open a comm to the frontend if one isn't already open."""
         if self.comm is None:
             args = dict(target_name='ipython.widget',
                         data={'model_name': self._model_name,
                               'model_module': self._model_module})
             if self._model_id is not None:
                 args['comm_id'] = self._model_id
-            self.comm = Comm(**args)
+            self.set_comm(Comm(**args))
+            
+            # first update
+            self.send_state()
+
+    def set_comm(self, comm):
+        """Set's the comm of the widget."""
+        self.comm = comm
             self._model_id = self.model_id
             
             self.comm.on_msg(self._handle_msg)
             Widget.widgets[self.model_id] = self
 
-            # first update
-            self.send_state()
-
     @property
     def model_id(self):
         """Gets the model id of this widget.
 
         If a Comm doesn't exist yet, a Comm will be created automagically."""
         return self.comm.comm_id
 
     #-------------------------------------------------------------------------
     # Methods
     #-------------------------------------------------------------------------
 
     def close(self):
         """Close method.
 
         Closes the underlying comm.
         When the comm is closed, all of the widget views are automatically
         removed from the front-end."""
         if self.comm is not None:
             Widget.widgets.pop(self.model_id, None)
             self.comm.close()
             self.comm = None
     
     def send_state(self, key=None):
         """Sends the widget state, or a piece of it, to the front-end.
 
         Parameters
         ----------
         key : unicode, or iterable (optional)
             A single property's name or iterable of property names to sync with the front-end.
         """
         self._send({
             "method" : "update",
             "state"  : self.get_state(key=key)
         })
 
     def get_state(self, key=None):
         """Gets the widget state, or a piece of it.
 
         Parameters
         ----------
         key : unicode or iterable (optional)
             A single property's name or iterable of property names to get.
         """
         if key is None:
             keys = self.keys
         elif isinstance(key, string_types):
             keys = [key]
         elif isinstance(key, collections.Iterable):
             keys = key
         else:
             raise ValueError("key must be a string, an iterable of keys, or None")
         state = {}
         for k in keys:
             f = self.trait_metadata(k, 'to_json', self._trait_to_json)
             value = getattr(self, k)
             state[k] = f(value)
         return state
 
     def set_state(self, sync_data):
         """Called when a state is received from the front-end."""
         for name in self.keys:
             if name in sync_data:
                 json_value = sync_data[name]
                 from_json = self.trait_metadata(name, 'from_json', self._trait_from_json)
                 with self._lock_property(name, json_value):
                     setattr(self, name, from_json(json_value))
     
     def send(self, content):
         """Sends a custom msg to the widget model in the front-end.
 
         Parameters
         ----------
         content : dict
             Content of the message to send.
         """
         self._send({"method": "custom", "content": content})
 
     def on_msg(self, callback, remove=False):
         """(Un)Register a custom msg receive callback.
 
         Parameters
         ----------
         callback: callable
             callback will be passed two arguments when a message arrives::
             
                 callback(widget, content)
             
         remove: bool
             True if the callback should be unregistered."""
         self._msg_callbacks.register_callback(callback, remove=remove)
 
     def on_displayed(self, callback, remove=False):
         """(Un)Register a widget displayed callback.
 
         Parameters
         ----------
         callback: method handler
             Must have a signature of::
             
                 callback(widget, **kwargs)
             
             kwargs from display are passed through without modification.
         remove: bool
             True if the callback should be unregistered."""
         self._display_callbacks.register_callback(callback, remove=remove)
 
     #-------------------------------------------------------------------------
     # Support methods
     #-------------------------------------------------------------------------
     @contextmanager
     def _lock_property(self, key, value):
         """Lock a property-value pair.
 
         The value should be the JSON state of the property.
 
         NOTE: This, in addition to the single lock for all state changes, is 
         flawed.  In the future we may want to look into buffering state changes 
         back to the front-end."""
         self._property_lock = (key, value)
         try:
             yield
         finally:
             self._property_lock = (None, None)
 
     @contextmanager
     def hold_sync(self):
         """Hold syncing any state until the context manager is released"""
         # We increment a value so that this can be nested.  Syncing will happen when
         # all levels have been released.
         self._send_state_lock += 1
         try:
             yield
         finally:
             self._send_state_lock -=1
             if self._send_state_lock == 0:
                 self.send_state(self._states_to_send)
                 self._states_to_send.clear()
 
     def _should_send_property(self, key, value):
         """Check the property lock (property_lock)"""
         to_json = self.trait_metadata(key, 'to_json', self._trait_to_json)
         if (key == self._property_lock[0]
             and to_json(value) == self._property_lock[1]):
             return False
         elif self._send_state_lock > 0:
             self._states_to_send.add(key)
             return False
         else:
             return True
     
     # Event handlers
     @_show_traceback
     def _handle_msg(self, msg):
         """Called when a msg is received from the front-end"""
         data = msg['content']['data']
         method = data['method']
         if not method in ['backbone', 'custom']:
             self.log.error('Unknown front-end to back-end widget msg with method "%s"' % method)
 
         # Handle backbone sync methods CREATE, PATCH, and UPDATE all in one.
         if method == 'backbone' and 'sync_data' in data:
             sync_data = data['sync_data']
             self.set_state(sync_data) # handles all methods
 
         # Handle a custom msg from the front-end
         elif method == 'custom':
             if 'content' in data:
                 self._handle_custom_msg(data['content'])
 
     def _handle_custom_msg(self, content):
         """Called when a custom msg is received."""
         self._msg_callbacks(self, content)
     
     def _notify_trait(self, name, old_value, new_value):
         """Called when a property has been changed."""
         # Trigger default traitlet callback machinery.  This allows any user
         # registered validation to be processed prior to allowing the widget
         # machinery to handle the state.
         LoggingConfigurable._notify_trait(self, name, old_value, new_value)
 
         # Send the state after the user registered callbacks for trait changes
         # have all fired (allows for user to validate values).
         if self.comm is not None and name in self.keys:
             # Make sure this isn't information that the front-end just sent us.
             if self._should_send_property(name, new_value):
                 # Send new state to front-end
                 self.send_state(key=name)
 
     def _handle_displayed(self, **kwargs):
         """Called when a view has been displayed for this widget instance"""
         self._display_callbacks(self, **kwargs)
 
     def _trait_to_json(self, x):
         """Convert a trait value to json
 
         Traverse lists/tuples and dicts and serialize their values as well.
         Replace any widgets with their model_id
         """
         if isinstance(x, dict):
             return {k: self._trait_to_json(v) for k, v in x.items()}
         elif isinstance(x, (list, tuple)):
             return [self._trait_to_json(v) for v in x]
         elif isinstance(x, Widget):
             return "IPY_MODEL_" + x.model_id
         else:
             return x # Value must be JSON-able
 
     def _trait_from_json(self, x):
         """Convert json values to objects
 
         Replace any strings representing valid model id values to Widget references.
         """
         if isinstance(x, dict):
             return {k: self._trait_from_json(v) for k, v in x.items()}
         elif isinstance(x, (list, tuple)):
             return [self._trait_from_json(v) for v in x]
         elif isinstance(x, string_types) and x.startswith('IPY_MODEL_') and x[10:] in Widget.widgets:
             # we want to support having child widgets at any level in a hierarchy
             # trusting that a widget UUID will not appear out in the wild
             return Widget.widgets[x[10:]]
         else:
             return x
 
     def _ipython_display_(self, **kwargs):
         """Called when `IPython.display.display` is called on the widget."""
         # Show view.
         if self._view_name is not None:
             self._send({"method": "display"})
             self._handle_displayed(**kwargs)
 
     def _send(self, msg):
         """Sends a message to the model in the front-end."""
         self.comm.send(msg)
 
 
 class DOMWidget(Widget):
     visible = Bool(True, help="Whether the widget is visible.", sync=True)
     _css = Tuple(sync=True, help="CSS property list: (selector, key, value)")
     _dom_classes = Tuple(sync=True, help="DOM classes applied to widget.$el.")
     
     width = CUnicode(sync=True)
     height = CUnicode(sync=True)
     padding = CUnicode(sync=True)
     margin = CUnicode(sync=True)
 
     color = Unicode(sync=True)
     background_color = Unicode(sync=True)
     border_color = Unicode(sync=True)
 
     border_width = CUnicode(sync=True)
     border_radius = CUnicode(sync=True)
     border_style = CaselessStrEnum(values=[ # http://www.w3schools.com/cssref/pr_border-style.asp
         'none', 
         'hidden', 
         'dotted', 
         'dashed', 
         'solid', 
         'double', 
         'groove', 
         'ridge', 
         'inset', 
         'outset', 
         'initial', 
         'inherit', ''],
         default_value='', sync=True)
 
     font_style = CaselessStrEnum(values=[ # http://www.w3schools.com/cssref/pr_font_font-style.asp
         'normal', 
         'italic', 
         'oblique', 
         'initial', 
         'inherit', ''], 
         default_value='', sync=True)
     font_weight = CaselessStrEnum(values=[ # http://www.w3schools.com/cssref/pr_font_weight.asp
         'normal', 
         'bold', 
         'bolder', 
         'lighter',
         'initial', 
         'inherit', ''] + [str(100 * (i+1)) for i in range(9)], 
         default_value='', sync=True)
     font_size = CUnicode(sync=True)
     font_family = Unicode(sync=True)
 
     def __init__(self, *pargs, **kwargs):
         super(DOMWidget, self).__init__(*pargs, **kwargs)
 
         def _validate_border(name, old, new):
             if new is not None and new != '':
                 if name != 'border_width' and not self.border_width:
                     self.border_width = 1
                 if name != 'border_style' and self.border_style == '':
                     self.border_style = 'solid'
         self.on_trait_change(_validate_border, ['border_width', 'border_style', 'border_color'])

IPython/kernel/comm/manager.py

@@ -1,150 +1,156 b''
 """Base class to manage comms"""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import sys
 
 from IPython.config import LoggingConfigurable
 from IPython.core.prompts import LazyEvaluate
 from IPython.core.getipython import get_ipython
 
 from IPython.utils.importstring import import_item
 from IPython.utils.py3compat import string_types
 from IPython.utils.traitlets import Instance, Unicode, Dict, Any
 
 from .comm import Comm
 
 
 def lazy_keys(dikt):
     """Return lazy-evaluated string representation of a dictionary's keys
     
     Key list is only constructed if it will actually be used.
     Used for debug-logging.
     """
     return LazyEvaluate(lambda d: list(d.keys()))
 
 
 class CommManager(LoggingConfigurable):
     """Manager for Comms in the Kernel"""
     
     # 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.kernel.iopub_socket
     session = Instance('IPython.kernel.zmq.session.Session')
     def _session_default(self):
         return self.kernel.session
     
     comms = Dict()
     targets = Dict()
     
     # Public APIs
     
     def register_target(self, target_name, f):
         """Register a callable f for a given target name
         
         f will be called with two arguments when a comm_open message is received with `target`:
         
         - the Comm instance
         - the `comm_open` message itself.
         
         f can be a Python callable or an import string for one.
         """
         if isinstance(f, string_types):
             f = import_item(f)
         
         self.targets[target_name] = f
     
     def unregister_target(self, target_name, f):
         """Unregister a callable registered with register_target"""
         return self.targets.pop(target_name);
     
     def register_comm(self, comm):
         """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
     
     def unregister_comm(self, comm):
         """Unregister a comm, and close its counterpart"""
         # unlike get_comm, this should raise a KeyError
         comm = self.comms.pop(comm.comm_id)
     
     def get_comm(self, comm_id):
         """Get a comm with a particular id
         
         Returns the comm if found, otherwise None.
         
         This will not raise an error,
         it will log messages if the comm cannot be found.
         """
         if comm_id not in self.comms:
             self.log.error("No such comm: %s", comm_id)
             self.log.debug("Current comms: %s", lazy_keys(self.comms))
             return
         # call, because we store weakrefs
         comm = self.comms[comm_id]
         return comm
     
     # Message handlers
     def comm_open(self, stream, ident, msg):
         """Handler for comm_open messages"""
         content = msg['content']
         comm_id = content['comm_id']
         target_name = content['target_name']
         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,
         )
+        self.register_comm(comm)
         if f is None:
             self.log.error("No such comm target registered: %s", target_name)
-            comm.close()
-            return
+        else:
         try:
             f(comm, msg)
+                return
         except Exception:
             self.log.error("Exception opening comm with target: %s", target_name, exc_info=True)
+        
+        # Failure.
+        try:
             comm.close()
+        except:
+            pass # Eat errors, nomnomnom
     
     def comm_msg(self, stream, ident, msg):
         """Handler for comm_msg messages"""
         content = msg['content']
         comm_id = content['comm_id']
         comm = self.get_comm(comm_id)
         if comm is None:
             # no such comm
             return
         try:
             comm.handle_msg(msg)
         except Exception:
             self.log.error("Exception in comm_msg for %s", comm_id, exc_info=True)
     
     def comm_close(self, stream, ident, msg):
         """Handler for comm_close messages"""
         content = msg['content']
         comm_id = content['comm_id']
         comm = self.get_comm(comm_id)
         if comm is None:
             # no such comm
             self.log.debug("No such comm to close: %s", comm_id)
             return
         del self.comms[comm_id]
         
         try:
             comm.handle_close(msg)
         except Exception:
             self.log.error("Exception handling comm_close for %s", comm_id, exc_info=True)
 
 
 __all__ = ['CommManager']