[Python-checkins] bpo-46080: fix argparse help generation exception in edge case (GH-30111)

[miss-islington]

https://github.com/python/cpython/commit/c6691a7ccbd027298ea2486014b55db037fffc9f
commit: c6691a7ccbd027298ea2486014b55db037fffc9f
branch: 3.9
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: miss-islington <31488909+miss-islington at users.noreply.github.com>
date: 2022-01-20T15:22:50-08:00
summary:

bpo-46080: fix argparse help generation exception in edge case (GH-30111)


Fix an uncaught exception during help text generation when
argparse.BooleanOptionalAction is used with default=argparse.SUPPRESS
and help is specified.
(cherry picked from commit 9e87c0e03fa501fb90008547983ce4c1dcaaf90c)

Co-authored-by: Felix Fontein <felix at fontein.de>

files:
A Misc/NEWS.d/next/Library/2021-12-15-06-29-00.bpo-46080.AuQpLt.rst
M Lib/argparse.py
M Lib/test/test_argparse.py

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 40569437ac62b..fbdfd5172fb35 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -878,7 +878,7 @@ def __init__(self,
                 option_string = '--no-' + option_string[2:]
                 _option_strings.append(option_string)
 
-        if help is not None and default is not None:
+        if help is not None and default is not None and default is not SUPPRESS:
             help += " (default: %(default)s)"
 
         super().__init__(
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index cc5e8491b4c49..5c86583ce10a4 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -3597,6 +3597,8 @@ class TestHelpUsage(HelpTestCase):
         Sig('--bar', help='Whether to bar', default=True,
                      action=argparse.BooleanOptionalAction),
         Sig('-f', '--foobar', '--barfoo', action=argparse.BooleanOptionalAction),
+        Sig('--bazz', action=argparse.BooleanOptionalAction,
+                      default=argparse.SUPPRESS, help='Bazz!'),
     ]
     argument_group_signatures = [
         (Sig('group'), [
@@ -3609,8 +3611,8 @@ class TestHelpUsage(HelpTestCase):
     usage = '''\
         usage: PROG [-h] [-w W [W ...]] [-x [X ...]] [--foo | --no-foo]
                     [--bar | --no-bar]
-                    [-f | --foobar | --no-foobar | --barfoo | --no-barfoo] [-y [Y]]
-                    [-z Z Z Z]
+                    [-f | --foobar | --no-foobar | --barfoo | --no-barfoo]
+                    [--bazz | --no-bazz] [-y [Y]] [-z Z Z Z]
                     a b b [c] [d ...] e [e ...]
         '''
     help = usage + '''\
@@ -3627,6 +3629,7 @@ class TestHelpUsage(HelpTestCase):
           --foo, --no-foo       Whether to foo
           --bar, --no-bar       Whether to bar (default: True)
           -f, --foobar, --no-foobar, --barfoo, --no-barfoo
+          --bazz, --no-bazz     Bazz!
 
         group:
           -y [Y]                y
diff --git a/Misc/NEWS.d/next/Library/2021-12-15-06-29-00.bpo-46080.AuQpLt.rst b/Misc/NEWS.d/next/Library/2021-12-15-06-29-00.bpo-46080.AuQpLt.rst
new file mode 100644
index 0000000000000..e42d84e31e759
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-12-15-06-29-00.bpo-46080.AuQpLt.rst
@@ -0,0 +1,3 @@
+Fix exception in argparse help text generation if a
+:class:`argparse.BooleanOptionalAction` argument's default is
+``argparse.SUPPRESS`` and it has ``help`` specified.  Patch by Felix Fontein.
\ No newline at end of file