commit bd8ca9aaccef0569c4b5c2e6dad0feb869ffd6c5
author Raymond Hettinger <rhettinger@users.noreply.github.com> Fri Aug 30 15:25:38 2019 -0700
committer GitHub <noreply@github.com> Fri Aug 30 15:25:38 2019 -0700
tree 6759b09299601a85a6f0f531e0157584d093ec7e
parent 4bd1d05ee247f200e52fab3958d875bd88073e5b

[3.8] bpo-29553: Fix ArgumentParser.format_usage() for mutually exclusive groups (GH-14976) (GH-15494) (GH-15624)

Lib/argparse.py

diff --git a/Lib/argparse.py b/Lib/argparse.py
index a6ab3b3..456ec8b 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -405,13 +405,19 @@
                             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] = '|'