Closes #17521: Merged fix from 3.3.

Lib/logging/config.py

@@ -175,8 +175,8 @@ def _handle_existing_loggers(existing, child_loggers, disable_existing):
             logger.level = logging.NOTSET
             logger.handlers = []
             logger.propagate = True
-        elif disable_existing:
+        else:
-            logger.disabled = True
+            logger.disabled = disable_existing
 
 def _install_loggers(cp, handlers, disable_existing):
     """Create and install loggers"""

Lib/test/test_logging.py

@@ -1261,9 +1261,30 @@ class ConfigFileTest(BaseTest):
     datefmt=
     """
 
-    def apply_config(self, conf):
+    disable_test = """
+    [loggers]
+    keys=root
+
+    [handlers]
+    keys=screen
+
+    [formatters]
+    keys=
+
+    [logger_root]
+    level=DEBUG
+    handlers=screen
+
+    [handler_screen]
+    level=DEBUG
+    class=StreamHandler
+    args=(sys.stdout,)
+    formatter=
+    """
+
+    def apply_config(self, conf, **kwargs):
         file = io.StringIO(textwrap.dedent(conf))
-        logging.config.fileConfig(file)
+        logging.config.fileConfig(file, **kwargs)
 
     def test_config0_ok(self):
         # A simple config file which overrides the default settings.
@@ -1385,6 +1406,15 @@ class ConfigFileTest(BaseTest):
             # Original logger output is empty.
             self.assert_log_lines([])
 
+    def test_logger_disabling(self):
+        self.apply_config(self.disable_test)
+        logger = logging.getLogger('foo')
+        self.assertFalse(logger.disabled)
+        self.apply_config(self.disable_test)
+        self.assertTrue(logger.disabled)
+        self.apply_config(self.disable_test, disable_existing_loggers=False)
+        self.assertFalse(logger.disabled)
+
 
 @unittest.skipUnless(threading, 'Threading required for this test.')
 class SocketHandlerTest(BaseTest):

Misc/NEWS

@@ -294,6 +294,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17521: Corrected non-enabling of logger following two calls to
+  fileConfig().
+
 - Issue #17508: Corrected MemoryHandler configuration in dictConfig() where
   the target handler wasn't configured first.