Implement a context manager as a property locking mechanism in Widget.

IPython/html/widgets/widget.py

@@ -1,411 +1,419 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
+from contextlib import contextmanager
 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
 #-----------------------------------------------------------------------------
+@contextmanager
+def PropertyLock(instance, key, value):
+    instance._property_lock = (key, value)
+    yield
+    del instance._property_lock
+
+def should_send_property(instance, key, value):
+    return not hasattr(instance, _property_lock) or \
+    key != instance._property_lock[0] or \
+    value != instance._property_lock[1]
+
 
 class Widget(LoggingConfigurable):
 
     # Shared declarations (Class level)
     widget_construction_callback = None
 
     keys = ['view_name']
 
     def on_widget_constructed(callback):
         """Class method, 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
 
     def _call_widget_constructed(widget):
         """Class 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)
 
     
 
     # Public declarations (Instance level)
     target_name = Unicode('widget', help="""Name of the backbone model 
         registered in the frontend to create and sync this widget with.""")
     view_name = Unicode(help="""Default view registered in the frontend
         to use to represent the widget.""")
 
     # Private/protected declarations
-    # todo: change this to a context manager
-    _property_lock = (None, None) # Last updated (key, value) from the front-end.  Prevents echo.
     _comm = Instance('IPython.kernel.comm.Comm')
     
     def __init__(self, **kwargs):
         """Public constructor
         """
         self._display_callbacks = []
         self._msg_callbacks = []
         super(Widget, self).__init__(**kwargs)
 
         self.on_trait_change(self._handle_property_changed, self.keys)
         Widget._call_widget_constructed(self)
 
     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._close_communication()
     
     @property
     def comm(self):
         if self._comm is None:
             self._open_communication()
         return self._comm
     
     @property
     def model_id(self):
         return self.comm.comm_id
 
     # Event handlers
     def _handle_msg(self, msg):
         """Called when a msg is recieved from the frontend"""
         data = msg['content']['data']
         method = data['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._handle_recieve_state(sync_data) # handles all methods
 
         # Handle a custom msg from the front-end
         elif method == 'custom':
             if 'custom_content' in data:
                 self._handle_custom_msg(data['custom_content'])
 
 
     def _handle_recieve_state(self, sync_data):
         """Called when a state is recieved from the frontend."""
         for name in self.keys:
             if name in sync_data:
-                try:
-                    self._property_lock = (name, sync_data[name])
-                    setattr(self, name, sync_data[name])
-                finally:
-                    self._property_lock = (None, None)
+                value = sync_data[name]
+                with PropertyLock(self, name, value):
+                    setattr(self, name, value)
 
 
     def _handle_custom_msg(self, content):
         """Called when a custom msg is recieved."""
         for handler in self._msg_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 == 1:
                     handler(content)
                 elif nargs == 2:
                     handler(self, content)
                 else:
                     raise TypeError('Widget msg callback must ' \
                         'accept 1 or 2 arguments, not %d.' % nargs)
 
 
     def _handle_property_changed(self, name, old, new):
         """Called when a property has been changed."""
         # Make sure this isn't information that the front-end just sent us.
-        if self._property_lock[0] != name and self._property_lock[1] != new:
+        if should_send_property(self, name, new):
             # Send new state to frontend
             self.send_state(key=name)
 
     def _handle_displayed(self, **kwargs):
         """Called when a view has been displayed for this widget instance"""
         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)
                 else:
                     handler(self, **kwargs)
 
     # 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.
         """
         self._send({"method": "update",
             "state": self.get_state()})
 
     def get_state(self, key=None):
         """Gets the widget state, or a piece of it.
 
         Parameters
         ----------
         key : unicode (optional)
             A single property's name to get.
         """
         state = {}
 
         # If a key is provided, just send the state of that key.
         if key is None:
             keys = self.keys[:]
         else:
             keys = [key]
         for k in keys:
             value = getattr(self, k)
 
             # a more elegant solution to encoding Widgets would be
             # to tap into the JSON encoder and teach it how to deal
             # with Widget objects, or maybe just teach the JSON
             # encoder to look for a _repr_json property before giving
             # up encoding
             if isinstance(value, Widget):
                 value = value.model_id
             elif isinstance(value, list) and len(value)>0 and isinstance(value[0], Widget):
                 # assume all elements of the list are widgets
                 value = [i.model_id for i in value]
             state[k] = value
         return state
 
 
     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",
             "custom_content": content})
 
 
     def on_msg(self, callback, remove=False):
         """Register a callback for when a custom msg is recieved from the front-end
 
         Parameters
         ----------
         callback: method handler
             Can have a signature of:
             - callback(content)
             - callback(sender, content)
         remove: bool
             True if the callback should be unregistered."""
         if remove and callback in self._msg_callbacks:
             self._msg_callbacks.remove(callback)
         elif not remove and not callback in self._msg_callbacks:
             self._msg_callbacks.append(callback)
 
 
     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, **kwargs)
               kwargs from display call passed through without modification.
         remove: bool
             True if the callback should be unregistered."""
         if remove and callback in self._display_callbacks:
             self._display_callbacks.remove(callback)
         elif not remove and not callback in self._display_callbacks:
             self._display_callbacks.append(callback)
 
 
     # Support methods
     def _repr_widget_(self, **kwargs):
         """Function that is called when `IPython.display.display` is called on
         the widget."""
             
         # Show view.  By sending a display message, the comm is opened and the
         # initial state is sent.
         self._send({"method": "display"})
         self._handle_displayed(**kwargs)
 
 
     def _open_communication(self):
         """Opens a communication with the front-end."""
         # 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._close_communication)
 
         # first update
         self.send_state()
 
 
     def _close_communication(self):
         """Closes a communication with the front-end."""
         if self._comm is not None:
             try:
                 self._comm.close()
             finally:
                 self._comm = None
 
 
     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 or not the widget is visible.")
 
     # Private/protected declarations
     _css = Dict() # Internal CSS property dict
 
     keys = ['visible', '_css'] + Widget.keys
 
     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():
                     if not (key in self._css[selector] and value in self._css[selector][key]):
                         self._css[selector][key] = value
                 self.send_state('_css')
             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_names, selector=""):
         """Add class[es] to a DOM element
 
         Parameters
         ----------
         class_names: unicode or list
             Class name(s) to add to the DOM element(s).
         selector: unicode (optional)
             JQuery selector to select the DOM element(s) that the class(es) will
             be added to.
         """
         class_list = class_names
         if isinstance(list, class_list):
             class_list = ' '.join(class_list)
 
         self.send({"msg_type": "add_class",
             "class_list": class_list,
             "selector": selector})
 
 
     def remove_class(self, class_names, selector=""):
         """Remove class[es] from a DOM element
 
         Parameters
         ----------
         class_names: unicode or list
             Class name(s) to remove from  the DOM element(s).
         selector: unicode (optional)
             JQuery selector to select the DOM element(s) that the class(es) will
             be removed from.
         """
         class_list = class_names
         if isinstance(list, class_list):
             class_list = ' '.join(class_list)
 
         self.send({"msg_type": "remove_class",
             "class_list": class_list,
             "selector": selector})