From 4f935ba4ad6b6bb16123dacd2768bb9b044752b3 2015-03-23 18:51:20
From: Thomas Kluyver <takowl@gmail.com>
Date: 2015-03-23 18:51:20
Subject: [PATCH] Merge pull request #8114 from minrk/delay_trait_notifications

add HasTraits.hold_trait_notifications
---

diff --git a/IPython/config/configurable.py b/IPython/config/configurable.py
index 3402f07..51a8fd0 100644
--- a/IPython/config/configurable.py
+++ b/IPython/config/configurable.py
@@ -69,6 +69,11 @@ class Configurable(HasTraits):
             self.parent = parent
         
         config = kwargs.pop('config', None)
+        
+        # load kwarg traits, other than config
+        super(Configurable, self).__init__(**kwargs)
+        
+        # load config
         if config is not None:
             # We used to deepcopy, but for now we are trying to just save
             # by reference.  This *could* have side effects as all components
@@ -81,9 +86,12 @@ class Configurable(HasTraits):
         else:
             # allow _config_default to return something
             self._load_config(self.config)
-        # This should go second so individual keyword arguments override
-        # the values in config.
-        super(Configurable, self).__init__(**kwargs)
+        
+        # Ensure explicit kwargs are applied after loading config.
+        # This is usually redundant, but ensures config doesn't override
+        # explicitly assigned values.
+        for key, value in kwargs.items():
+            setattr(self, key, value)
 
     #-------------------------------------------------------------------------
     # Static trait notifiations
@@ -130,17 +138,20 @@ class Configurable(HasTraits):
             section_names = self.section_names()
         
         my_config = self._find_my_config(cfg)
-        for name, config_value in iteritems(my_config):
-            if name in traits:
-                if isinstance(config_value, LazyConfigValue):
-                    # ConfigValue is a wrapper for using append / update on containers
-                    # without having to copy the 
-                    initial = getattr(self, name)
-                    config_value = config_value.get_value(initial)
-                # 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))
+        
+        # hold trait notifications until after all config has been loaded
+        with self.hold_trait_notifications():
+            for name, config_value in iteritems(my_config):
+                if name in traits:
+                    if isinstance(config_value, LazyConfigValue):
+                        # ConfigValue is a wrapper for using append / update on containers
+                        # without having to copy the initial value
+                        initial = getattr(self, name)
+                        config_value = config_value.get_value(initial)
+                    # 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.
diff --git a/IPython/utils/tests/test_traitlets.py b/IPython/utils/tests/test_traitlets.py
index 30d82a9..1b364f7 100644
--- a/IPython/utils/tests/test_traitlets.py
+++ b/IPython/utils/tests/test_traitlets.py
@@ -1330,6 +1330,78 @@ def test_pickle_hastraits():
         nt.assert_equal(c2.i, c.i)
         nt.assert_equal(c2.j, c.j)
 
+
+def test_hold_trait_notifications():
+    changes = []
+    class Test(HasTraits):
+        a = Integer(0)
+        def _a_changed(self, name, old, new):
+            changes.append((old, new))
+    
+    t = Test()
+    with t.hold_trait_notifications():
+        with t.hold_trait_notifications():
+            t.a = 1
+            nt.assert_equal(t.a, 1)
+            nt.assert_equal(changes, [])
+        t.a = 2
+        nt.assert_equal(t.a, 2)
+        with t.hold_trait_notifications():
+            t.a = 3
+            nt.assert_equal(t.a, 3)
+            nt.assert_equal(changes, [])
+            t.a = 4
+            nt.assert_equal(t.a, 4)
+            nt.assert_equal(changes, [])
+        t.a = 4
+        nt.assert_equal(t.a, 4)
+        nt.assert_equal(changes, [])
+    nt.assert_equal(changes, [(0,1), (1,2), (2,3), (3,4)])
+
+
+class OrderTraits(HasTraits):
+    notified = Dict()
+    
+    a = Unicode()
+    b = Unicode()
+    c = Unicode()
+    d = Unicode()
+    e = Unicode()
+    f = Unicode()
+    g = Unicode()
+    h = Unicode()
+    i = Unicode()
+    j = Unicode()
+    k = Unicode()
+    l = Unicode()
+    
+    def _notify(self, name, old, new):
+        """check the value of all traits when each trait change is triggered
+        
+        This verifies that the values are not sensitive
+        to dict ordering when loaded from kwargs
+        """
+        # check the value of the other traits
+        # when a given trait change notification fires
+        self.notified[name] = {
+            c: getattr(self, c) for c in 'abcdefghijkl'
+        }
+    
+    def __init__(self, **kwargs):
+        self.on_trait_change(self._notify)
+        super(OrderTraits, self).__init__(**kwargs)
+
+def test_notification_order():
+    d = {c:c for c in 'abcdefghijkl'}
+    obj = OrderTraits()
+    nt.assert_equal(obj.notified, {})
+    obj = OrderTraits(**d)
+    notifications = {
+        c: d for c in 'abcdefghijkl'
+    }
+    nt.assert_equal(obj.notified, notifications)
+
+
 class TestEventful(TestCase):
 
     def test_list(self):
diff --git a/IPython/utils/traitlets.py b/IPython/utils/traitlets.py
index 7d3c5f1..f2fb877 100644
--- a/IPython/utils/traitlets.py
+++ b/IPython/utils/traitlets.py
@@ -575,8 +575,36 @@ class HasTraits(py3compat.with_metaclass(MetaHasTraits, object)):
         # Allow trait values to be set using keyword arguments.
         # We need to use setattr for this to trigger validation and
         # notifications.
-        for key, value in iteritems(kw):
-            setattr(self, key, value)
+        
+        with self.hold_trait_notifications():
+            for key, value in iteritems(kw):
+                setattr(self, key, value)
+    
+    @contextlib.contextmanager
+    def hold_trait_notifications(self):
+        """Context manager for bundling trait change notifications
+        
+        Use this when doing multiple trait assignments (init, config),
+        to avoid race conditions in trait notifiers requesting other trait values.
+        All trait notifications will fire after all values have been assigned.
+        """
+        _notify_trait = self._notify_trait
+        notifications = []
+        self._notify_trait = lambda *a: notifications.append(a)
+        
+        try:
+            yield
+        finally:
+            self._notify_trait = _notify_trait
+            if isinstance(_notify_trait, types.MethodType):
+                # FIXME: remove when support is bumped to 3.4.
+                # when original method is restored,
+                # remove the redundant value from __dict__
+                # (only used to preserve pickleability on Python < 3.4)
+                self.__dict__.pop('_notify_trait', None)
+        # trigger delayed notifications
+        for args in notifications:
+            self._notify_trait(*args)
 
     def _notify_trait(self, name, old_value, new_value):