From 38520218b0b44bb82a69b81c3e9bc91d50b5fb66 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <raymond.hettinger@gmail.com>
Date: Fri, 30 Aug 2019 14:46:42 -0700
Subject: [PATCH] [3.8] bpo-29553: Fix ArgumentParser.format_usage() for
 mutually exclusive groups (GH-14976) (GH-15494)

---
 Lib/argparse.py           | 10 ++++++++--
 Lib/test/test_argparse.py | 40 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/Lib/argparse.py b/Lib/argparse.py
index a6ab3b3b898d4b..456ec8bb7fc86a 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -405,13 +405,19 @@ def _format_actions_usage(self, actions, groups):
                             inserts[start] += ' ['
                         else:
                             inserts[start] = '['
-                        inserts[end] = ']'
+                        if end in inserts:
+                            inserts[end] += ']'
+                        else:
+                            inserts[end] = ']'
                     else:
                         if start in inserts:
                             inserts[start] += ' ('
                         else:
                             inserts[start] = '('
-                        inserts[end] = ')'
+                        if end in inserts:
+                            inserts[end] += ')'
+                        else:
+                            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
index d6d16090eb0260..86ec6cca51acc4 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -2813,6 +2813,46 @@ 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
+
+    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
+        '''
+
+    # We are only interested in testing the behavior of format_usage().
+    test_failures_when_not_required = None
+    test_failures_when_required = None
+    test_successes_when_not_required = None
+    test_successes_when_required = None
+
 # =================================================
 # Mutually exclusive group in parent parser tests
 # =================================================