allow multi-level Config parentage

now Foo.Bar.Baz can affect a Baz whose parent is Bar whose parent is Foo.

More specificity = higher priority, so Foo.Bar.Baz > Bar.Baz > Baz.

IPython/config/configurable.py

@@ -64,8 +64,8 b' class Configurable(HasTraits):'
             If this is empty, default values are used. If config is a
             :class:`Config` instance, it will be used to configure the
             instance.
-        parent : Configurable instance
-            The parent
+        parent : Configurable instance, optional
+            The parent Configurable instance of this object.
 
         Notes
         -----
@@ -112,6 +112,31 b' class Configurable(HasTraits):'
         return  [c.__name__ for c in reversed(cls.__mro__) if
             issubclass(c, Configurable) and issubclass(cls, c)
         ]
+    
+    def _find_my_config(self, cfg):
+        """extract my config from a global Config object
+        
+        will construct a Config object of only the config values that apply to me
+        based on my mro(), as well as those of my parent(s) if they exist.
+        
+        If I am Bar and my parent is Foo, and their parent is Tim,
+        this will return merge following config sections, in this order::
+        
+            [Bar, Foo.bar, Tim.Foo.Bar]
+        
+        With the last item being the highest priority.
+        """
+        cfgs = [cfg]
+        if self.parent:
+            cfgs.append(self.parent._find_my_config(cfg))
+        my_config = Config()
+        for c in cfgs:
+            for sname in self.section_names():
+                # Don't do a blind getattr as that would cause the config to
+                # dynamically create the section with name Class.__name__.
+                if c._has_section(sname):
+                    my_config.merge(c[sname])
+        return my_config
 
     def _load_config(self, cfg, section_names=None, traits=None):
         """load traits from a Config object"""
@@ -121,24 +146,13 b' class Configurable(HasTraits):'
         if section_names is None:
             section_names = self.section_names()
         
-        for sname in section_names:
-            # Don't do a blind getattr as that would cause the config to
-            # dynamically create the section with name self.__class__.__name__.
-            if cfg._has_section(sname):
-                my_config = cfg[sname]
-                for k, v in traits.iteritems():
-                    try:
-                        # Here we grab the value from the config
-                        # If k has the naming convention of a config
-                        # section, it will be auto created.
-                        config_value = my_config[k]
-                    except KeyError:
-                        pass
-                    else:
-                        # We have to do a deepcopy here if we don't deepcopy the entire
-                        # config object. If we don't, a mutable config_value will be
-                        # shared by all instances, effectively making it a class attribute.
-                        setattr(self, k, deepcopy(config_value))
+        my_config = self._find_my_config(cfg)
+        for name, config_value in my_config.iteritems():
+            if name in traits:
+                # We have to do a deepcopy here if we don't deepcopy the entire
+                # config object. If we don't, a mutable config_value will be
+                # shared by all instances, effectively making it a class attribute.
+                setattr(self, name, deepcopy(config_value))
 
     def _config_changed(self, name, old, new):
         """Update all the class traits having ``config=True`` as metadata.
@@ -155,13 +169,6 b' class Configurable(HasTraits):'
         # and works down the mro loading the config for each section.
         section_names = self.section_names()
         self._load_config(new, traits=traits, section_names=section_names)
-        
-        # load parent config as well, if we have one
-        parent_section_names = [] if self.parent is None else self.parent.section_names()
-        for parent in parent_section_names:
-            if not new._has_section(parent):
-                continue
-            self._load_config(new[parent], traits=traits, section_names=section_names)
 
     def update_config(self, config):
         """Fire the traits events when the config is updated."""

IPython/config/tests/test_configurable.py

@@ -192,7 +192,6 b' class MyParent2(MyParent):'
 class TestParentConfigurable(TestCase):
     
     def test_parent_config(self):
-        
         cfg = Config({
             'MyParent' : {
                 'MyConfigurable' : {
@@ -205,7 +204,6 b' class TestParentConfigurable(TestCase):'
         self.assertEqual(myc.b, parent.config.MyParent.MyConfigurable.b)
 
     def test_parent_inheritance(self):
-        
         cfg = Config({
             'MyParent' : {
                 'MyConfigurable' : {
@@ -217,8 +215,26 b' class TestParentConfigurable(TestCase):'
         myc = MyConfigurable(parent=parent)
         self.assertEqual(myc.b, parent.config.MyParent.MyConfigurable.b)
 
+    def test_multi_parent(self):
+        cfg = Config({
+            'MyParent2' : {
+                'MyParent' : {
+                    'MyConfigurable' : {
+                        'b' : 2.0,
+                    }
+                },
+                # this one shouldn't count
+                'MyConfigurable' : {
+                    'b' : 3.0,
+                },
+            }
+        })
+        parent2 = MyParent2(config=cfg)
+        parent = MyParent(parent=parent2)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent2.MyParent.MyConfigurable.b)
+
     def test_parent_priority(self):
-        
         cfg = Config({
             'MyConfigurable' : {
                 'b' : 2.0,
@@ -237,3 +253,32 b' class TestParentConfigurable(TestCase):'
         parent = MyParent2(config=cfg)
         myc = MyConfigurable(parent=parent)
         self.assertEqual(myc.b, parent.config.MyParent2.MyConfigurable.b)
+
+    def test_multi_parent_priority(self):
+        cfg = Config({
+            'MyConfigurable' : {
+                'b' : 2.0,
+            },
+            'MyParent' : {
+                'MyConfigurable' : {
+                    'b' : 3.0,
+                }
+            },
+            'MyParent2' : {
+                'MyConfigurable' : {
+                    'b' : 4.0,
+                }
+            },
+            'MyParent2' : {
+                'MyParent' : {
+                    'MyConfigurable' : {
+                        'b' : 5.0,
+                    }
+                }
+            }
+        })
+        parent2 = MyParent2(config=cfg)
+        parent = MyParent2(parent=parent2)
+        myc = MyConfigurable(parent=parent)
+        self.assertEqual(myc.b, parent.config.MyParent2.MyParent.MyConfigurable.b)
+