Issue #18920: argparse's default version action (for -v, --version) should

output to stdout, matching the 'python -v'

Reported by Wolfgang Maier

Lib/argparse.py

@@ -1037,7 +1037,8 @@ class _VersionAction(Action):
             version = parser.version
         formatter = parser._get_formatter()
         formatter.add_text(version)
-        parser.exit(message=formatter.format_help())
+        parser._print_message(formatter.format_help(), _sys.stdout)
+        parser.exit()
 
 
 class _SubParsersAction(Action):

Lib/test/test_argparse.py

@@ -4359,7 +4359,7 @@ class TestOptionalsHelpVersionActions(TestCase):
     def test_version_format(self):
         parser = ErrorRaisingArgumentParser(prog='PPP')
         parser.add_argument('-v', '--version', action='version', version='%(prog)s 3.5')
-        msg = self._get_error(parser.parse_args, ['-v']).stderr
+        msg = self._get_error(parser.parse_args, ['-v']).stdout
         self.assertEqual('PPP 3.5\n', msg)
 
     def test_version_no_help(self):
@@ -4372,7 +4372,7 @@ class TestOptionalsHelpVersionActions(TestCase):
     def test_version_action(self):
         parser = ErrorRaisingArgumentParser(prog='XXX')
         parser.add_argument('-V', action='version', version='%(prog)s 3.7')
-        msg = self._get_error(parser.parse_args, ['-V']).stderr
+        msg = self._get_error(parser.parse_args, ['-V']).stdout
         self.assertEqual('XXX 3.7\n', msg)
 
     def test_no_help(self):

Misc/NEWS

@@ -193,6 +193,9 @@ Library
   existing directory caused mkstemp and related APIs to fail instead of
   retrying. Report and fix by Vlad Shcherbina.
 
+- Issue #18920: argparse's default destination for the version action (-v,
+  --version) has also been changed to stdout, to match the Python executable.
+
 Tests
 -----