gh-105376: Restore deprecated logging warn() method (#122775)

This reverts commit dcc028d924 and
commit 6c54e5d721.

Keep the deprecated logging warn() method in Python 3.13.

Co-authored-by: Gregory P. Smith <greg@krypto.org>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Doc/deprecations/pending-removal-in-future.rst

@@ -67,6 +67,9 @@ although there is currently no date scheduled for their removal.
   * ``EntryPoints`` tuple interface.
   * Implicit ``None`` on return values.
 
+* :mod:`logging`: the ``warn()`` method has been deprecated
+  since Python 3.3, use :meth:`~logging.warning()` instead.
+
 * :mod:`mailbox`: Use of StringIO input and text mode is deprecated, use
   BytesIO and binary mode instead.
 

Doc/library/logging.rst

@@ -352,10 +352,6 @@ in a module, ``__name__`` is the module's name in the Python package namespace.
       .. versionchanged:: 3.8
          The *stacklevel* parameter was added.
 
-      .. versionchanged:: 3.13
-         Remove the undocumented ``warn()`` method which was an alias to the
-         :meth:`warning` method.
-
 
    .. method:: Logger.info(msg, *args, **kwargs)
 
@@ -368,6 +364,10 @@ in a module, ``__name__`` is the module's name in the Python package namespace.
       Logs a message with level :const:`WARNING` on this logger. The arguments are
       interpreted as for :meth:`debug`.
 
+      .. note:: There is an obsolete method ``warn`` which is functionally
+         identical to ``warning``. As ``warn`` is deprecated, please do not use
+         it - use ``warning`` instead.
+
    .. method:: Logger.error(msg, *args, **kwargs)
 
       Logs a message with level :const:`ERROR` on this logger. The arguments are
@@ -1124,11 +1124,6 @@ information into logging calls. For a usage example, see the section on
       Attribute :attr:`!manager` and method :meth:`!_log` were added, which
       delegate to the underlying logger and allow adapters to be nested.
 
-   .. versionchanged:: 3.13
-
-      Remove the undocumented :meth:`!warn`` method which was an alias to the
-      :meth:`!warning` method.
-
    .. versionchanged:: 3.13
 
       The *merge_extra* argument was added.
@@ -1224,10 +1219,6 @@ functions.
       identical to ``warning``. As ``warn`` is deprecated, please do not use
       it - use ``warning`` instead.
 
-   .. versionchanged:: 3.13
-      Remove the undocumented ``warn()`` function which was an alias to the
-      :func:`warning` function.
-
 
 .. function:: error(msg, *args, **kwargs)
 

Doc/whatsnew/3.13.rst

@@ -1397,16 +1397,6 @@ locale
   use ``locale.setlocale(locale.LC_ALL, "")`` instead.
   (Contributed by Victor Stinner in :gh:`104783`.)
 
-logging
--------
-
-* :mod:`logging`: Remove undocumented and untested ``Logger.warn()`` and
-  ``LoggerAdapter.warn()`` methods and ``logging.warn()`` function. Deprecated
-  since Python 3.3, they were aliases to the :meth:`logging.Logger.warning`
-  method, :meth:`!logging.LoggerAdapter.warning` method and
-  :func:`logging.warning` function.
-  (Contributed by Victor Stinner in :gh:`105376`.)
-
 pathlib
 -------
 

Lib/logging/__init__.py

@@ -37,7 +37,7 @@ __all__ = ['BASIC_FORMAT', 'BufferingFormatter', 'CRITICAL', 'DEBUG', 'ERROR',
            'captureWarnings', 'critical', 'debug', 'disable', 'error',
            'exception', 'fatal', 'getLevelName', 'getLogger', 'getLoggerClass',
            'info', 'log', 'makeLogRecord', 'setLoggerClass', 'shutdown',
-           'warning', 'getLogRecordFactory', 'setLogRecordFactory',
+           'warn', 'warning', 'getLogRecordFactory', 'setLogRecordFactory',
            'lastResort', 'raiseExceptions', 'getLevelNamesMapping',
            'getHandlerByName', 'getHandlerNames']
 
@@ -1530,6 +1530,11 @@ class Logger(Filterer):
         if self.isEnabledFor(WARNING):
             self._log(WARNING, msg, args, **kwargs)
 
+    def warn(self, msg, *args, **kwargs):
+        warnings.warn("The 'warn' method is deprecated, "
+            "use 'warning' instead", DeprecationWarning, 2)
+        self.warning(msg, *args, **kwargs)
+
     def error(self, msg, *args, **kwargs):
         """
         Log 'msg % args' with severity 'ERROR'.
@@ -1906,6 +1911,11 @@ class LoggerAdapter(object):
         """
         self.log(WARNING, msg, *args, **kwargs)
 
+    def warn(self, msg, *args, **kwargs):
+        warnings.warn("The 'warn' method is deprecated, "
+            "use 'warning' instead", DeprecationWarning, 2)
+        self.warning(msg, *args, **kwargs)
+
     def error(self, msg, *args, **kwargs):
         """
         Delegate an error call to the underlying logger.
@@ -2169,6 +2179,11 @@ def warning(msg, *args, **kwargs):
         basicConfig()
     root.warning(msg, *args, **kwargs)
 
+def warn(msg, *args, **kwargs):
+    warnings.warn("The 'warn' function is deprecated, "
+        "use 'warning' instead", DeprecationWarning, 2)
+    warning(msg, *args, **kwargs)
+
 def info(msg, *args, **kwargs):
     """
     Log a message with severity 'INFO' on the root logger. If the logger has

Misc/NEWS.d/next/Library/2024-08-07-14-12-19.gh-issue-105376.QbGPdE.rst

@@ -0,0 +1,3 @@
+Restore the deprecated :mod:`logging` ``warn()`` method. It was removed in
+Python 3.13 alpha 1. Keep the deprecated ``warn()`` method in Python 3.13.
+Patch by Victor Stinner.