Closes #13235: Added deprecation for warn() methods and function in logging.

Doc/library/logging.rst

@@ -189,6 +189,9 @@ instantiated directly, but always through the module-level function
    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)
 
@@ -880,8 +883,12 @@ functions.
 
 .. function:: warning(msg, *args, **kwargs)
 
-   Logs a message with level :const:`WARNING` on the root logger. The arguments are
+   Logs a message with level :const:`WARNING` on the root logger. The arguments
-   interpreted as for :func:`debug`.
+   are interpreted as for :func:`debug`.
+
+   .. note:: There is an obsolete function `warn()` which is functionally
+      identical to `warning()`. As `warn()` is deprecated, please do not use
+      it - use `warning()` instead.
 
 
 .. function:: error(msg, *args, **kwargs)

Lib/logging/__init__.py

@@ -1243,7 +1243,10 @@ class Logger(Filterer):
         if self.isEnabledFor(WARNING):
             self._log(WARNING, msg, args, **kwargs)
 
-    warn = warning
+    def warn(self, msg, *args, **kwargs):
+        warnings.warn("The 'warn' method is deprecated, "
+            "use 'warning' instead", PendingDeprecationWarning, 2)
+        self.warning(msg, *args, **kwargs)
 
     def error(self, msg, *args, **kwargs):
         """
@@ -1556,7 +1559,10 @@ class LoggerAdapter(object):
         """
         self.log(WARNING, msg, *args, **kwargs)
 
-    warn = warning
+    def warn(self, msg, *args, **kwargs):
+        warnings.warn("The 'warn' method is deprecated, "
+            "use 'warning' instead", PendingDeprecationWarning, 2)
+        self.warning(msg, *args, **kwargs)
 
     def error(self, msg, *args, **kwargs):
         """
@@ -1766,7 +1772,10 @@ def warning(msg, *args, **kwargs):
         basicConfig()
     root.warning(msg, *args, **kwargs)
 
-warn = warning
+def warn(msg, *args, **kwargs):
+    warnings.warn("The 'warn' function is deprecated, "
+        "use 'warning' instead", PendingDeprecationWarning, 2)
+    warning(msg, *args, **kwargs)
 
 def info(msg, *args, **kwargs):
     """

Misc/NEWS

@@ -326,6 +326,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #13235: Added PendingDeprecationWarning to warn() method and function.
+
 - Issue #9168: now smtpd is able to bind privileged port.
 
 - Issue #12529: fix cgi.parse_header issue on strings with double-quotes and