add tag observing to HasTraits.observe

traitlets/traitlets.py

@@ -1004,7 +1004,7 @@ def on_trait_change(self, handler=None, name=None, remove=False):
         else:
             self.observe(_callback_wrapper(handler), names=name)
 
-    def observe(self, handler, names=All, type='change'):
+    def observe(self, handler, names=All, tags=None, type='change'):
         """Setup a handler to be called when a trait changes.
 
         This is used to setup dynamic notifications of trait changes.
@@ -1026,15 +1026,20 @@ def observe(self, handler, names=All, type='change'):
             If names is All, the handler will apply to all traits.  If a list
             of str, handler will apply to all names in the list.  If a
             str, the handler will apply just to that name.
+        tags: dict
+            Applies the handler to all traits whose metadata matches the given
+            tags or selector functions (`HasTraits.traits` for selector info)
         type : str, All (default: 'change')
             The type of notification to filter by. If equal to All, then all
             notifications are passed to the observe handler.
         """
         names = parse_notifier_name(names)
+        if tags:
+            names.extend(self.trait_names(**tags))
         for n in names:
             self._add_notifiers(handler, n, type)
 
-    def unobserve(self, handler, names=All, type='change'):
+    def unobserve(self, handler, names=All, tags=None, type='change'):
         """Remove a trait change handler.
 
         This is used to unregister handlers to trait change notificiations.
@@ -1047,11 +1052,16 @@ def unobserve(self, handler, names=All, type='change'):
             The names of the traits for which the specified handler should be
             uninstalled. If names is All, the specified handler is uninstalled
             from the list of notifiers corresponding to all changes.
+        tags: dict
+            Removes the handler from all traits whose metadata matches the given
+            tags or selector functions (`HasTraits.traits` for selector info)
         type : str or All (default: 'change')
             The type of notification to filter by. If All, the specified handler
             is uninstalled from the list of notifiers corresponding to all types.
         """
         names = parse_notifier_name(names)
+        if tags:
+            names.extend(self.trait_names(**tags))
         for n in names:
             self._remove_notifiers(handler, n, type)