gh-58282: Fix support of tuple metavar for positional arguments in argparse (GH-124782)

Previously, formatting help output or error message for positional argument
with a tuple metavar raised exception.

Co-authored-by: Cyker Way <cykerway@gmail.com>

Lib/argparse.py

@@ -527,8 +527,7 @@ class HelpFormatter(object):
     def _format_action_invocation(self, action):
         if not action.option_strings:
             default = self._get_default_metavar_for_positional(action)
-            metavar, = self._metavar_formatter(action, default)(1)
+            return ' '.join(self._metavar_formatter(action, default)(1))
-            return metavar
 
         else:
 
@@ -703,7 +702,15 @@ def _get_action_name(argument):
     elif argument.option_strings:
         return '/'.join(argument.option_strings)
     elif argument.metavar not in (None, SUPPRESS):
-        return argument.metavar
+        metavar = argument.metavar
+        if not isinstance(metavar, tuple):
+            return metavar
+        if argument.nargs == ZERO_OR_MORE and len(metavar) == 2:
+            return '%s[, %s]' % metavar
+        elif argument.nargs == ONE_OR_MORE:
+            return '%s[, %s]' % metavar
+        else:
+            return ', '.join(metavar)
     elif argument.dest not in (None, SUPPRESS):
         return argument.dest
     elif argument.choices:

Lib/test/test_argparse.py

@@ -4898,7 +4898,7 @@ class TestHelpNone(HelpTestCase):
     version = ''
 
 
-class TestHelpTupleMetavar(HelpTestCase):
+class TestHelpTupleMetavarOptional(HelpTestCase):
     """Test specifying metavar as a tuple"""
 
     parser_signature = Sig(prog='PROG')
@@ -4925,6 +4925,34 @@ class TestHelpTupleMetavar(HelpTestCase):
     version = ''
 
 
+class TestHelpTupleMetavarPositional(HelpTestCase):
+    """Test specifying metavar on a Positional as a tuple"""
+
+    parser_signature = Sig(prog='PROG')
+    argument_signatures = [
+        Sig('w', help='w help', nargs='+', metavar=('W1', 'W2')),
+        Sig('x', help='x help', nargs='*', metavar=('X1', 'X2')),
+        Sig('y', help='y help', nargs=3, metavar=('Y1', 'Y2', 'Y3')),
+        Sig('z', help='z help', nargs='?', metavar=('Z1',)),
+    ]
+    argument_group_signatures = []
+    usage = '''\
+        usage: PROG [-h] W1 [W2 ...] [X1 [X2 ...]] Y1 Y2 Y3 [Z1]
+        '''
+    help = usage + '''\
+
+        positional arguments:
+          W1 W2       w help
+          X1 X2       x help
+          Y1 Y2 Y3    y help
+          Z1          z help
+
+        options:
+          -h, --help  show this help message and exit
+        '''
+    version = ''
+
+
 class TestHelpRawText(HelpTestCase):
     """Test the RawTextHelpFormatter"""
 
@@ -6521,6 +6549,27 @@ class TestExitOnError(TestCase):
                                'the following arguments are required: bar, baz$',
                                self.parser.parse_args, [])
 
+    def test_required_args_with_metavar(self):
+        self.parser.add_argument('bar')
+        self.parser.add_argument('baz', metavar='BaZ')
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'the following arguments are required: bar, BaZ$',
+                               self.parser.parse_args, [])
+
+    def test_required_args_n(self):
+        self.parser.add_argument('bar')
+        self.parser.add_argument('baz', nargs=3)
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'the following arguments are required: bar, baz$',
+                               self.parser.parse_args, [])
+
+    def test_required_args_n_with_metavar(self):
+        self.parser.add_argument('bar')
+        self.parser.add_argument('baz', nargs=3, metavar=('B', 'A', 'Z'))
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'the following arguments are required: bar, B, A, Z$',
+                               self.parser.parse_args, [])
+
     def test_required_args_optional(self):
         self.parser.add_argument('bar')
         self.parser.add_argument('baz', nargs='?')
@@ -6535,6 +6584,20 @@ class TestExitOnError(TestCase):
                                'the following arguments are required: bar$',
                                self.parser.parse_args, [])
 
+    def test_required_args_one_or_more(self):
+        self.parser.add_argument('bar')
+        self.parser.add_argument('baz', nargs='+')
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'the following arguments are required: bar, baz$',
+                               self.parser.parse_args, [])
+
+    def test_required_args_one_or_more_with_metavar(self):
+        self.parser.add_argument('bar')
+        self.parser.add_argument('baz', nargs='+', metavar=('BaZ1', 'BaZ2'))
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               r'the following arguments are required: bar, BaZ1\[, BaZ2]$',
+                               self.parser.parse_args, [])
+
     def test_required_args_remainder(self):
         self.parser.add_argument('bar')
         self.parser.add_argument('baz', nargs='...')
@@ -6550,6 +6613,39 @@ class TestExitOnError(TestCase):
                                'one of the arguments --bar --baz is required',
                                self.parser.parse_args, [])
 
+    def test_conflicting_mutually_exclusive_args_optional_with_metavar(self):
+        group = self.parser.add_mutually_exclusive_group()
+        group.add_argument('--bar')
+        group.add_argument('baz', nargs='?', metavar='BaZ')
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'argument BaZ: not allowed with argument --bar$',
+                               self.parser.parse_args, ['--bar', 'a', 'b'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'argument --bar: not allowed with argument BaZ$',
+                               self.parser.parse_args, ['a', '--bar', 'b'])
+
+    def test_conflicting_mutually_exclusive_args_zero_or_more_with_metavar1(self):
+        group = self.parser.add_mutually_exclusive_group()
+        group.add_argument('--bar')
+        group.add_argument('baz', nargs='*', metavar=('BAZ1',))
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'argument BAZ1: not allowed with argument --bar$',
+                               self.parser.parse_args, ['--bar', 'a', 'b'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               'argument --bar: not allowed with argument BAZ1$',
+                               self.parser.parse_args, ['a', '--bar', 'b'])
+
+    def test_conflicting_mutually_exclusive_args_zero_or_more_with_metavar2(self):
+        group = self.parser.add_mutually_exclusive_group()
+        group.add_argument('--bar')
+        group.add_argument('baz', nargs='*', metavar=('BAZ1', 'BAZ2'))
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               r'argument BAZ1\[, BAZ2]: not allowed with argument --bar$',
+                               self.parser.parse_args, ['--bar', 'a', 'b'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                               r'argument --bar: not allowed with argument BAZ1\[, BAZ2]$',
+                               self.parser.parse_args, ['a', '--bar', 'b'])
+
     def test_ambiguous_option(self):
         self.parser.add_argument('--foobaz')
         self.parser.add_argument('--fooble', action='store_true')

Misc/NEWS.d/next/Library/2018-12-04-07-36-27.bpo-14074.fMLKCu.rst

@@ -0,0 +1,2 @@
+Fix :mod:`argparse` metavar processing to allow positional arguments to have a
+tuple metavar.