use observe in traitlets.config

traitlets/config/application.py

@@ -22,7 +22,7 @@
 )
 
 from traitlets.traitlets import (
-    Unicode, List, Enum, Dict, Instance, TraitError
+    Unicode, List, Enum, Dict, Instance, TraitError, observe, default
 )
 from ipython_genutils.importstring import import_item
 from ipython_genutils.text import indent, wrap_paragraphs, dedent
@@ -177,7 +177,7 @@ def _log_format_changed(self, name, old, new):
         _log_formatter = self._log_formatter_cls(fmt=new, datefmt=self.log_datefmt)
         _log_handler.setFormatter(_log_formatter)
 
-
+    @default('log')
     def _log_default(self):
         """Start logging for this application.
 
@@ -215,12 +215,14 @@ def _log_default(self):
     # this must be a dict of two-tuples, the first element being the Config/dict
     # and the second being the help string for the flag
     flags = Dict()
-    def _flags_changed(self, name, old, new):
+    @observe('flags')
+    def _flags_changed(self, change):
         """ensure flags dict is valid"""
-        for key,value in iteritems(new):
-            assert len(value) == 2, "Bad flag: %r:%s"%(key,value)
-            assert isinstance(value[0], (dict, Config)), "Bad flag: %r:%s"%(key,value)
-            assert isinstance(value[1], string_types), "Bad flag: %r:%s"%(key,value)
+        new = change['new']
+        for key, value in new.items():
+            assert len(value) == 2, "Bad flag: %r:%s" % (key, value)
+            assert isinstance(value[0], (dict, Config)), "Bad flag: %r:%s" % (key, value)
+            assert isinstance(value[1], string_types), "Bad flag: %r:%s" % (key, value)
 
 
     # subcommands for launching other applications
@@ -242,11 +244,12 @@ def __init__(self, **kwargs):
         # options and config files.
         if self.__class__ not in self.classes:
             self.classes.insert(0, self.__class__)
-
-    def _config_changed(self, name, old, new):
-        SingletonConfigurable._config_changed(self, name, old, new)
+
+    @observe('config')
+    def _config_changed(self, change):
+        super(Application, self)._config_changed(change)
         self.log.debug('Config changed:')
-        self.log.debug(repr(new))
+        self.log.debug(repr(change['new']))
 
     @catch_config_error
     def initialize(self, argv=None):

traitlets/config/configurable.py

@@ -6,11 +6,10 @@
 
 from __future__ import print_function
 
-import logging
 from copy import deepcopy
 
 from .loader import Config, LazyConfigValue
-from traitlets.traitlets import HasTraits, Instance
+from traitlets.traitlets import HasTraits, Instance, observe, default
 from ipython_genutils.text import indent, dedent, wrap_paragraphs
 from ipython_genutils.py3compat import iteritems
 
@@ -162,8 +161,8 @@ def _load_config(self, cfg, section_names=None, traits=None):
                         self.log.warning(u"Config option `{option}` not recognized by `{klass}`, do you mean one of : `{matches}`"
                                 .format(option=name, klass=type(self).__name__, matches=' ,'.join(matches)))
 
-
-    def _config_changed(self, name, old, new):
+    @observe('config')
+    def _config_changed(self, change):
         """Update all the class traits having ``config=True`` in metadata.
 
         For any class trait with a ``config`` metadata attribute that is
@@ -177,7 +176,7 @@ def _config_changed(self, name, old, new):
         # classes that are Configurable subclasses.  This starts with Configurable
         # 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)
+        self._load_config(change['new'], traits=traits, section_names=section_names)
 
     def update_config(self, config):
         """Update config and trigger reload of config via trait events"""
@@ -329,6 +328,7 @@ class LoggingConfigurable(Configurable):
     """
 
     log = Instance('logging.Logger')
+    @default('log')
     def _log_default(self):
         from traitlets import log
         return log.get_logger()