GH-103219: Fix optional args incorrectly being processed as required args

Lib/argparse.py

@@ -2130,7 +2130,9 @@ def consume_positionals(start_index):
         required_actions = []
         for action in self._actions:
             if action not in seen_actions:
-                if action.required:
+                if (action.required and
+                    action.default is None and
+                    action.nargs not in (ZERO_OR_MORE, OPTIONAL)):
                     required_actions.append(_get_action_name(action))
                 else:
                     # Convert action default now instead of doing it before

Lib/test/test_argparse.py

@@ -6091,6 +6091,13 @@ def test_required_args(self):
                                'the following arguments are required: bar, baz',
                                self.parser.parse_args, [])
 
+    def test_required_and_optional(self):
+        self.parser.add_argument('bar')
+        self.parser.add_argument('baz', nargs='*')
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'the following arguments are required: bar',
+                               self.parser.parse_args, [])
+
     def test_required_mutually_exclusive_args(self):
         group = self.parser.add_mutually_exclusive_group(required=True)
         group.add_argument('--bar')

Misc/NEWS.d/next/Library/2024-09-11-03-21-56.gh-issue-103219.F5atBD.rst

@@ -0,0 +1 @@
+Fixes a bug in argparse where optional args are incorrectly processed as required args