Do not configure the root logger.

tornado/ioloop.py

@@ -32,7 +32,6 @@
 import errno
 import functools
 import heapq
-import logging
 import numbers
 import os
 import select
@@ -42,7 +41,7 @@
 import traceback
 
 from tornado.concurrent import Future, TracebackFuture
-from tornado.log import app_log, gen_log
+from tornado.log import app_log, gen_log, check_log_handlers
 from tornado import stack_context
 from tornado.util import Configurable
 
@@ -541,15 +540,7 @@ def set_blocking_signal_threshold(self, seconds, action):
                           action if action is not None else signal.SIG_DFL)
 
     def start(self):
-        if not logging.getLogger().handlers:
-            # The IOLoop catches and logs exceptions, so it's
-            # important that log output be visible.  However, python's
-            # default behavior for non-root loggers (prior to python
-            # 3.2) is to print an unhelpful "no handlers could be
-            # found" message rather than the actual log entry, so we
-            # must explicitly configure logging if we've made it this
-            # far without anything.
-            logging.basicConfig()
+        check_log_handlers()
         if self._stopped:
             self._stopped = False
             return

tornado/log.py

@@ -49,6 +49,27 @@
 gen_log = logging.getLogger("tornado.general")
 
 
+def _basic_config(logger):
+    logger.addHandler(logging.StreamHandler())
+
+
+def check_log_handlers():
+    '''The IOLoop catches and logs exceptions, so it's
+    important that log output be visible.  However, python's
+    default behavior for non-root loggers (prior to python
+    3.2) is to print an unhelpful "no handlers could be
+    found" message rather than the actual log entry, so we
+    must explicitly configure logging if we've made it this
+    far without anything.
+    '''
+    for parent in (None, 'tornado'):
+        if logging.getLogger(parent).handlers:
+            return
+    for logger in (access_log, app_log, gen_log):
+        if not logger.handlers:
+            _basic_config(logger)
+
+
 def _stderr_supports_color():
     color = False
     if curses and sys.stderr.isatty():