don't instantiate Application just for default logger

It's unlikely to happen in IPython itself,
but can happen if config loaders are used elsewhere.

IPython/config/configurable.py

@@ -26,6 +26,7 b' from __future__ import print_function'
 # Imports
 #-----------------------------------------------------------------------------
 
+import logging
 from copy import deepcopy
 
 from .loader import Config, LazyConfigValue
@@ -381,6 +382,9 b' class LoggingConfigurable(Configurable):'
     log = Instance('logging.Logger')
     def _log_default(self):
         from IPython.config.application import Application
-        return Application.instance().log
+        if Application.initialized():
+            return Application.instance().log
+        else:
+            return logging.getLogger()
 
 

IPython/config/loader.py

@@ -25,6 +25,7 b' Authors'
 
 import argparse
 import copy
+import logging
 import os
 import re
 import sys
@@ -308,7 +309,10 b' class ConfigLoader(object):'
 
     def _log_default(self):
         from IPython.config.application import Application
-        return Application.instance().log
+        if Application.initialized():
+            return Application.instance().log
+        else:
+            return logging.getLogger()
 
     def __init__(self, log=None):
         """A base class for config loaders.