gh-115032: Deprecate support for custom logging handlers with 'strm' argument.

Author: felixxm

Doc/whatsnew/3.13.rst

@@ -629,6 +629,11 @@ Deprecated
   security and functionality bugs.  This includes removal of the ``--cgi``
   flag to the ``python -m http.server`` command line in 3.15.
 
+* :mod:`logging`: Support for custom logging handlers with the *strm* argument
+  is deprecated and scheduled for removal in Python 3.15. Define handlers with
+  the *stream* argument instead.
+  (Contributed by Mariusz Felisiak in :gh:`115032`.)
+
 * :mod:`pathlib`:
   :meth:`pathlib.PurePath.is_reserved` is deprecated and scheduled for
   removal in Python 3.15. Use :func:`os.path.isreserved` to detect reserved

Lib/logging/config.py

@@ -838,6 +838,8 @@ def configure_handler(self, config):
             else:
                 factory = klass
         kwargs = {k: config[k] for k in config if (k != '.' and valid_ident(k))}
+        # When deprecation ends for using the 'strm' parameter, remove the
+        # "except TypeError ..."
         try:
             result = factory(**kwargs)
         except TypeError as te:
@@ -849,6 +851,15 @@ def configure_handler(self, config):
             #(e.g. by Django)
             kwargs['strm'] = kwargs.pop('stream')
             result = factory(**kwargs)
+
+            import warnings
+            warnings.warn(
+                "Support for custom logging handlers with the 'strm' argument "
+                "is deprecated and scheduled for removal in Python 3.15. "
+                "Define handlers with the 'stream' argument instead.",
+                DeprecationWarning,
+                stacklevel=2,
+            )
         if formatter:
             result.setFormatter(formatter)
         if level is not None:

Lib/test/test_logging.py

@@ -3214,6 +3214,37 @@ def format(self, record):
         }
     }
 
+    # Remove when deprecation ends.
+    class DeprecatedStrmHandler(logging.StreamHandler):
+        def __init__(self, strm=None):
+            super().__init__(stream=strm)
+
+    config_custom_handler_with_deprecated_strm_arg = {
+        'version': 1,
+        'formatters': {
+            'form1' : {
+                'format' : '%(levelname)s ++ %(message)s',
+            },
+        },
+        'handlers' : {
+            'hand1' : {
+                'class' : DeprecatedStrmHandler,
+                'formatter' : 'form1',
+                'level' : 'NOTSET',
+                'stream'  : 'ext://sys.stdout',
+            },
+        },
+        'loggers' : {
+            'compiler.parser' : {
+                'level' : 'DEBUG',
+                'handlers' : ['hand1'],
+            },
+        },
+        'root' : {
+            'level' : 'WARNING',
+        },
+    }
+
     def apply_config(self, conf):
         logging.config.dictConfig(conf)
 
@@ -3303,6 +3334,15 @@ def test_config5_ok(self):
         self.test_config1_ok(config=self.config5)
         self.check_handler('hand1', CustomHandler)
 
+    def test_deprecation_warning_custom_handler_with_strm_arg(self):
+        msg = (
+            "Support for custom logging handlers with the 'strm' argument "
+            "is deprecated and scheduled for removal in Python 3.15. "
+            "Define handlers with the 'stream' argument instead."
+        )
+        with self.assertWarnsRegex(DeprecationWarning, msg):
+            self.test_config1_ok(config=self.config_custom_handler_with_deprecated_strm_arg)
+
     def test_config6_failure(self):
         self.assertRaises(Exception, self.apply_config, self.config6)
 

Misc/NEWS.d/next/Library/2024-02-11-21-43-20.gh-issue-115032.nsEkE_.rst

@@ -0,0 +1,3 @@
+Support for custom logging handlers with the *strm* argument is deprecated
+and scheduled for removal in Python 3.15. Define handlers with the *stream*
+argument instead. Patch by Mariusz Felisiak.