Closes python#28524: added default level for logging.disable().

Author: vsajip

Doc/library/logging.rst

@@ -1023,7 +1023,7 @@ functions.
       handlers being added multiple times to the root logger, which can in turn
       lead to multiple messages for the same event.
 
-.. function:: disable(lvl)
+.. function:: disable(lvl=CRITICAL)
 
    Provides an overriding level *lvl* for all loggers which takes precedence over
    the logger's own level. When the need arises to temporarily throttle logging
@@ -1036,6 +1036,14 @@ functions.
    overriding level, so that logging output again depends on the effective
    levels of individual loggers.
 
+   Note that if you have defined any custom logging level higher than
+   ``CRITICAL`` (this is not recommended), you won't be able to rely on the
+   default value for the *lvl* parameter, but will have to explicitly supply a
+   suitable value.
+
+   .. versionchanged:: 3.7
+      The *lvl* parameter was defaulted to level ``CRITICAL``. See Issue
+      #28524 for more information about this change.
 
 .. function:: addLevelName(lvl, levelName)
 

Lib/logging/__init__.py

@@ -1889,7 +1889,7 @@ def log(level, msg, *args, **kwargs):
         basicConfig()
     root.log(level, msg, *args, **kwargs)
 
-def disable(level):
+def disable(level=CRITICAL):
     """
     Disable all logging calls of severity 'level' and below.
     """

Lib/test/test_logging.py

@@ -3473,6 +3473,11 @@ def test_disable(self):
         logging.disable(83)
         self.assertEqual(logging.root.manager.disable, 83)
 
+        # test the default value introduced in 3.7
+        # (Issue #28524)
+        logging.disable()
+        self.assertEqual(logging.root.manager.disable, logging.CRITICAL)
+
     def _test_log(self, method, level=None):
         called = []
         support.patch(self, logging, 'basicConfig',