Added check on widget close to make sure comm isn't already none.

IPython/html/widgets/widget.py

@@ -1,353 +1,356 b''
 """Base Widget class.  Allows user to create widgets in the backend that render
 in the IPython notebook frontend.
 """
 #-----------------------------------------------------------------------------
 # 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 copy import copy
 from glob import glob
 import uuid
 import sys
 import os
 import inspect
 import types
 
 import IPython
 from IPython.kernel.comm import Comm
 from IPython.config import LoggingConfigurable
 from IPython.utils.traitlets import Unicode, Dict, List, Instance, Bool
 from IPython.display import Javascript, display
 from IPython.utils.py3compat import string_types
 
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 class Widget(LoggingConfigurable):
 
     # Shared declarations
     _keys = []
     
     # Public declarations
     target_name = Unicode('widget', help="""Name of the backbone model 
         registered in the frontend to create and sync this widget with.""")
     default_view_name = Unicode(help="""Default view registered in the frontend
         to use to represent the widget.""")
     parent = Instance('IPython.html.widgets.widget.Widget')
     visible = Bool(True, help="Whether or not the widget is visible.")
 
     def _parent_changed(self, name, old, new):
         if self._displayed:
             raise Exception('Parent cannot be set because widget has been displayed.')
         elif new == self:
             raise Exception('Parent cannot be set to self.')
         else:
 
             # Parent/child association
             if new is not None and not self in new._children:
                 new._children.append(self)
             if old is not None and self in old._children:
                 old._children.remove(self)                
 
     # Private/protected declarations
     _property_lock = False
     _css = Dict() # Internal CSS property dict
     _add_class = List() # Used to add a js class to a DOM element (call#, selector, class_name)
     _remove_class = List() # Used to remove a js class from a DOM element (call#, selector, class_name)
     _displayed = False
     _comm = None
     
     
     def __init__(self, **kwargs):
         """Public constructor
 
         Parameters
         ----------
         parent : Widget instance (optional)
             Widget that this widget instance is child of.  When the widget is
             displayed in the frontend, it's corresponding view will be made
             child of the parent's view if the parent's view exists already.  If
             the parent's view is displayed, it will automatically display this 
             widget's default view as it's child.  The default view can be set
             via the default_view_name property.
         """
         self._children = []
         self._add_class = [0]
         self._remove_class = [0]
         self._display_callbacks = []
         super(Widget, self).__init__(**kwargs)
                 
         # Register after init to allow default values to be specified
         self.on_trait_change(self._handle_property_changed, self.keys)
         
         
     def __del__(self):
         """Object disposal"""
         self.close()
     
 
     def close(self):
         """Close method.  Closes the widget which closes the underlying comm.
         When the comm is closed, all of the widget views are automatically 
         removed from the frontend."""
-        self._comm.close()
-        del self._comm
+        try:
+            self._comm.close()
+            del self._comm
+        except:
+            pass # Comm doesn't exist and/or is already closed.
     
     
     # Properties      
     def _get_keys(self):
         keys = ['visible', '_css', '_add_class', '_remove_class']
         keys.extend(self._keys)
         return keys
     keys = property(_get_keys)
     
     
     # Event handlers
     def _handle_msg(self, msg):
         """Called when a msg is recieved from the frontend"""
         # Handle backbone sync methods CREATE, PATCH, and UPDATE
         sync_method = msg['content']['data']['sync_method']
         sync_data = msg['content']['data']['sync_data']
         self._handle_recieve_state(sync_data) # handles all methods
     
     
     def _handle_recieve_state(self, sync_data):
         """Called when a state is recieved from the frontend."""
         self._property_lock = True
         try:
             
             # Use _keys instead of keys - Don't get retrieve the css from the client side.
             for name in self._keys:
                 if name in sync_data:
                     setattr(self, name, sync_data[name])
         finally:
             self._property_lock = False
     
     
     def _handle_property_changed(self, name, old, new):
         """Called when a proeprty has been changed."""
         if not self._property_lock and self._comm is not None:
             # TODO: Validate properties.
             # Send new state to frontend
             self.send_state(key=name)
 
 
     def _handle_close(self):
         """Called when the comm is closed by the frontend."""
         self._comm = None
     
     
     # Public methods
     def send_state(self, key=None):
         """Sends the widget state, or a piece of it, to the frontend.
 
         Parameters
         ----------
         key : unicode (optional)
             A single property's name to sync with the frontend.
         """
         if self._comm is not None:
             state = {}
 
             # If a key is provided, just send the state of that key.
             keys = []
             if key is None:
                 keys.extend(self.keys)
             else:
                 keys.append(key)
             for key in self.keys:
                 try:
                     state[key] = getattr(self, key)
                 except Exception as e:
                     pass # Eat errors, nom nom nom
             self._comm.send({"method": "update",
                             "state": state})
 
 
     def get_css(self, key, selector=""):
         """Get a CSS property of the widget.  Note, this function does not 
         actually request the CSS from the front-end;  Only properties that have 
         been set with set_css can be read.
 
         Parameters
         ----------
         key: unicode
             CSS key
         selector: unicode (optional)
             JQuery selector used when the CSS key/value was set.
         """
         if selector in self._css and key in self._css[selector]:
             return self._css[selector][key]
         else:
             return None
 
 
     def set_css(self, *args, **kwargs):
         """Set one or more CSS properties of the widget (shared among all of the 
         views).  This function has two signatures:
         - set_css(css_dict, [selector=''])
         - set_css(key, value, [selector=''])
 
         Parameters
         ----------
         css_dict : dict
             CSS key/value pairs to apply
         key: unicode
             CSS key
         value
             CSS value
         selector: unicode (optional)
             JQuery selector to use to apply the CSS key/value.
         """
         selector = kwargs.get('selector', '')
 
         # Signature 1: set_css(css_dict, [selector=''])
         if len(args) == 1:
             if isinstance(args[0], dict):
                 for (key, value) in args[0].items():
                     self.set_css(key, value, selector=selector)
             else:
                 raise Exception('css_dict must be a dict.')
 
         # Signature 2: set_css(key, value, [selector=''])
         elif len(args) == 2 or len(args) == 3:
 
             # Selector can be a positional arg if it's the 3rd value
             if len(args) == 3:
                 selector = args[2]
             if selector not in self._css:
                 self._css[selector] = {}
                 
             # Only update the property if it has changed.
             key = args[0]
             value = args[1]
             if not (key in self._css[selector] and value in self._css[selector][key]):
                 self._css[selector][key] = value
                 self.send_state('_css') # Send new state to client.
         else:
             raise Exception('set_css only accepts 1-3 arguments')
 
 
     def add_class(self, class_name, selector=""):
         """Add class[es] to a DOM element
 
         Parameters
         ----------
         class_name: unicode
             Class name(s) to add to the DOM element(s).  Multiple class names 
             must be space separated.
         selector: unicode (optional)
             JQuery selector to select the DOM element(s) that the class(es) will 
             be added to.
         """
         self._add_class = [self._add_class[0] + 1, selector, class_name]
         self.send_state(key='_add_class')
 
 
     def remove_class(self, class_name, selector=""):
         """Remove class[es] from a DOM element
 
         Parameters
         ----------
         class_name: unicode
             Class name(s) to remove from  the DOM element(s).  Multiple class 
             names must be space separated.
         selector: unicode (optional)
             JQuery selector to select the DOM element(s) that the class(es) will 
             be removed from.
         """
         self._remove_class = [self._remove_class[0] + 1, selector, class_name]
         self.send_state(key='_remove_class')
 
 
     def on_displayed(self, callback, remove=False):
         """Register a callback to be called when the widget has been displayed
 
         Parameters
         ----------
         callback: method handler
             Can have a signature of:
             - callback()
             - callback(sender)
             - callback(sender, view_name)
         remove: bool
             True if the callback should be unregistered."""
         if remove:
             self._display_callbacks.remove(callback)
         elif not callback in self._display_callbacks:
             self._display_callbacks.append(callback)
 
 
     def handle_displayed(self, view_name):
         """Called when a view has been displayed for this widget instance
 
         Parameters
         ----------
         view_name: unicode
             Name of the view that was displayed."""
         for handler in self._display_callbacks:
             if callable(handler):
                 argspec = inspect.getargspec(handler)
                 nargs = len(argspec[0])
 
                 # Bound methods have an additional 'self' argument
                 if isinstance(handler, types.MethodType):
                     nargs -= 1
 
                 # Call the callback
                 if nargs == 0:
                     handler()
                 elif nargs == 1:
                     handler(self)
                 elif nargs == 2:
                     handler(self, view_name)
                 else:
                     raise TypeError('Widget display callback must ' \
                         'accept 0-2 arguments, not %d.' % nargs)
 
 
     # Support methods
     def _repr_widget_(self, view_name=None):
         """Function that is called when `IPython.display.display` is called on
         the widget.
 
         Parameters
         ----------
         view_name: unicode (optional)
             View to display in the frontend.  Overrides default_view_name."""
 
         if not view_name:
             view_name = self.default_view_name
         
         # Create a comm.
         if self._comm is None:
             self._comm = Comm(target_name=self.target_name)
             self._comm.on_msg(self._handle_msg)
             self._comm.on_close(self._handle_close)
         
         # Make sure model is syncronized
         self.send_state()
             
         # Show view.
         if self.parent is None or self.parent._comm is None:
             self._comm.send({"method": "display", "view_name": view_name})
         else:
             self._comm.send({"method": "display", 
                             "view_name": view_name,
                             "parent": self.parent._comm.comm_id})
         self._displayed = True
         self.handle_displayed(view_name)
 
         # Now display children if any.
         for child in self._children:
             if child != self:
                 child._repr_widget_()
         return None