#10424: argument names are now included in the missing argument message

Fix and initial test patch by Michele Orrù.

Lib/argparse.py

@@ -1969,17 +1969,12 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         # if we didn't consume all the argument strings, there were extras
         extras.extend(arg_strings[stop_index:])
 
-        # if we didn't use all the Positional objects, there were too few
-        # arg strings supplied.
-        if positionals:
-            self.error(_('too few arguments'))
-
         # make sure all required actions were present
-        for action in self._actions:
-            if action.required:
-                if action not in seen_actions:
-                    name = _get_action_name(action)
-                    self.error(_('argument %s is required') % name)
+        required_actions = [_get_action_name(action) for action in self._actions
+                            if action.required and action not in seen_actions]
+        if required_actions:
+            self.error(_('the following arguments are required: %s') %
+                       ', '.join(required_actions))
 
         # make sure all required groups had one option present
         for group in self._mutually_exclusive_groups:

Lib/test/test_argparse.py

@@ -4480,6 +4480,67 @@ class TestArgumentTypeError(TestCase):
         else:
             self.fail()
 
+# =========================
+# MessageContentError tests
+# =========================
+
+class TestMessageContentError(TestCase):
+
+    def test_missing_argument_name_in_message(self):
+        parser = ErrorRaisingArgumentParser(prog='PROG', usage='')
+        parser.add_argument('req_pos', type=str)
+        parser.add_argument('-req_opt', type=int, required=True)
+        parser.add_argument('need_one', type=str, nargs='+')
+
+        with self.assertRaises(ArgumentParserError) as cm:
+            parser.parse_args([])
+        msg = str(cm.exception)
+        self.assertRegex(msg, 'req_pos')
+        self.assertRegex(msg, 'req_opt')
+        self.assertRegex(msg, 'need_one')
+        with self.assertRaises(ArgumentParserError) as cm:
+            parser.parse_args(['myXargument'])
+        msg = str(cm.exception)
+        self.assertNotIn(msg, 'req_pos')
+        self.assertRegex(msg, 'req_opt')
+        self.assertRegex(msg, 'need_one')
+        with self.assertRaises(ArgumentParserError) as cm:
+            parser.parse_args(['myXargument', '-req_opt=1'])
+        msg = str(cm.exception)
+        self.assertNotIn(msg, 'req_pos')
+        self.assertNotIn(msg, 'req_opt')
+        self.assertRegex(msg, 'need_one')
+
+    def test_optional_optional_not_in_message(self):
+        parser = ErrorRaisingArgumentParser(prog='PROG', usage='')
+        parser.add_argument('req_pos', type=str)
+        parser.add_argument('--req_opt', type=int, required=True)
+        parser.add_argument('--opt_opt', type=bool, nargs='?',
+                            default=True)
+        with self.assertRaises(ArgumentParserError) as cm:
+            parser.parse_args([])
+        msg = str(cm.exception)
+        self.assertRegex(msg, 'req_pos')
+        self.assertRegex(msg, 'req_opt')
+        self.assertNotIn(msg, 'opt_opt')
+        with self.assertRaises(ArgumentParserError) as cm:
+            parser.parse_args(['--req_opt=1'])
+        msg = str(cm.exception)
+        self.assertRegex(msg, 'req_pos')
+        self.assertNotIn(msg, 'req_opt')
+        self.assertNotIn(msg, 'opt_opt')
+
+    def test_optional_positional_not_in_message(self):
+        parser = ErrorRaisingArgumentParser(prog='PROG', usage='')
+        parser.add_argument('req_pos')
+        parser.add_argument('optional_positional', nargs='?', default='eggs')
+        with self.assertRaises(ArgumentParserError) as cm:
+            parser.parse_args([])
+        msg = str(cm.exception)
+        self.assertRegex(msg, 'req_pos')
+        self.assertNotIn(msg, 'optional_positional')
+
+
 # ======================
 # parse_known_args tests
 # ======================

Misc/NEWS

@@ -187,6 +187,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #10424: Argparse now includes the names of the missing required
+  arguments in the missing arguments error message.
+
 - Issue #12168: SysLogHandler now allows NUL termination to be controlled using
   a new 'append_nul' attribute on the handler.