python · andrewnester · Feb 15, 2017 · Feb 19, 2017 · Feb 19, 2017 · Feb 22, 2017
diff --git a/Lib/argparse.py b/Lib/argparse.py
@@ -396,18 +396,19 @@ def _format_actions_usage(self, actions, groups):
                 if actions[start:end] == group._group_actions:
                     for action in group._group_actions:
                         group_actions.add(action)
-                    if not group.required:
-                        if start in inserts:
-                            inserts[start] += ' ['
+                    if not isinstance(group._container, _MutuallyExclusiveGroup):
+                        if not group.required:
+                            if start in inserts:
+                                inserts[start] += ' ['
+                            else:
+                                inserts[start] = '['
+                            inserts[end] = ']'
                         else:
-                            inserts[start] = '['
-                        inserts[end] = ']'
-                    else:
-                        if start in inserts:
-                            inserts[start] += ' ('
-                        else:
-                            inserts[start] = '('
-                        inserts[end] = ')'
+                            if start in inserts:
+                                inserts[start] += ' ('
+                            else:
+                                inserts[start] = '('
+                            inserts[end] = ')'
                     for i in range(start + 1, end):
                         inserts[i] = '|'
 

diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
@@ -2362,6 +2362,26 @@ def test_help(self):
               '''
         self.assertEqual(parser.format_help(), textwrap.dedent(expected))
 
+    def test_help_required(self):
+        parser = ErrorRaisingArgumentParser(prog='PROG')
+        group1 = parser.add_mutually_exclusive_group(required=True)
+        group1.add_argument('--foo', action='store_true')
+        group1.add_argument('--bar', action='store_false')
+        group2 = parser.add_mutually_exclusive_group(required=True)
+        group2.add_argument('--soup', action='store_true')
+        group2.add_argument('--nuts', action='store_false')
+        expected = '''\
+            usage: PROG [-h] (--foo | --bar) (--soup | --nuts)
+
+            optional arguments:
+              -h, --help  show this help message and exit
+              --foo
+              --bar
+              --soup
+              --nuts
+              '''
+        self.assertEqual(parser.format_help(), textwrap.dedent(expected))
+
 class MEMixin(object):
 
     def test_failures_when_not_required(self):
@@ -2725,6 +2745,44 @@ def get_parser(self, required):
           -c          c help
         '''
 
+
+class TestMutuallyExclusiveNested(MEMixin, TestCase):
+    def get_parser(self, required):
+        parser = ErrorRaisingArgumentParser(prog='PROG')
+        group = parser.add_mutually_exclusive_group(required=required)
+        group.add_argument('-a')
+        group.add_argument('-b')
+        group2 = group.add_mutually_exclusive_group(required=required)
+        group2.add_argument('-c')
+        group2.add_argument('-d')
+        group3 = group2.add_mutually_exclusive_group(required=required)
+        group3.add_argument('-e')
+        group3.add_argument('-f')
+        return parser
+
+    failures = []
+    successes = []
+    successes_when_not_required = []
+
+    usage_when_not_required = '''\
+        usage: PROG [-h] [-a A | -b B | -c C | -d D | -e E | -f F]
+        '''
+    usage_when_required = '''\
+        usage: PROG [-h] (-a A | -b B | -c C | -d D | -e E | -f F)
+        '''
+
+    help = '''\
+
+        optional arguments:
+          -h, --help  show this help message and exit
+          -a A
+          -b B
+          -c C
+          -d D
+          -e E
+          -f F
+        '''
+
 # =================================================
 # Mutually exclusive group in parent parser tests
 # =================================================

diff --git a/Misc/NEWS b/Misc/NEWS
@@ -252,6 +252,8 @@ Library
 - bpo-29576: Improve some deprecations in importlib. Some deprecated methods
   now emit DeprecationWarnings and have better descriptive messages.
 
+- bpo-29553: Fixed ArgumentParses format_usage for mutually exclusive groups.
+
 - bpo-29534: Fixed different behaviour of Decimal.from_float()
   for _decimal and _pydecimal. Thanks Andrew Nester.