gh-132372: Batch logging cache clearing

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>

Author: esadomer

Lib/logging/config.py

@@ -188,15 +188,20 @@ def _handle_existing_loggers(existing, child_loggers, disable_existing):
     disabled if disable_existing is false.
     """
     root = logging.root
+    cache_clear_needed = False
     for log in existing:
         logger = root.manager.loggerDict[log]
         if log in child_loggers:
             if not isinstance(logger, logging.PlaceHolder):
-                logger.setLevel(logging.NOTSET)
+                # Equivalent to setLevel(NOTSET), but clear the cache once.
+                logger.level = logging.NOTSET
                 logger.handlers = []
                 logger.propagate = True
+                cache_clear_needed = True
         else:
             logger.disabled = disable_existing
+    if cache_clear_needed:
+        root.manager._clear_cache()
 
 def _discard_existing_logger(name, existing, existing_set, child_loggers):
     """Discard a configured logger and record its existing children."""

Lib/test/test_logging.py

@@ -4176,6 +4176,8 @@ def test_90195(self):
     def test_disable_existing_loggers_preserves_children(self):
         parent = logging.getLogger('many')
         child = logging.getLogger('many.child')
+        child.setLevel(logging.CRITICAL)
+        self.assertFalse(child.isEnabledFor(logging.INFO))
         cousin = logging.getLogger('many-child')
         for i in range(20):
             logging.getLogger(f'many-sibling-{i}')
@@ -4191,6 +4193,8 @@ def test_disable_existing_loggers_preserves_children(self):
 
         self.assertFalse(parent.disabled)
         self.assertFalse(child.disabled)
+        self.assertEqual(child.level, logging.NOTSET)
+        self.assertTrue(child.isEnabledFor(logging.INFO))
         self.assertTrue(cousin.disabled)
 
     def test_111615(self):