gh-88753: Make BooleanOptionalAction's addition of default to help more similar to other actions (#27808)

Help for other actions omit the default value if default is SUPPRESS or
already contains the special format string '%(default)'.  Add those
special cases to BooleanOptionalAction's help formatting too.

Fixes https://bugs.python.org/issue44587 so that default=SUPPRESS is not
emitted.

Fixes https://bugs.python.org/issue38956 as this code will detect
whether '%(default)s' has already been specified in the help string.

Signed-off-by: Micky Yun Chan (michiboo): <chanmickyyun@gmail.com>
Co-authored-by: Micky Yun Chan <michan@redhat.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index c47aeff..8d1a00a 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -153,6 +153,7 @@ def _copy_items(items):
 # Formatting Help
 # ===============
 
+
 class HelpFormatter(object):
     """Formatter for generating usage messages and argument help strings.
 
@@ -695,8 +696,19 @@ class ArgumentDefaultsHelpFormatter(HelpFormatter):
     """
 
     def _get_help_string(self, action):
+        """
+        Add the default value to the option help message.
+
+        ArgumentDefaultsHelpFormatter and BooleanOptionalAction when it isn't
+        already present. This code will do that, detecting cornercases to
+        prevent duplicates or cases where it wouldn't make sense to the end
+        user.
+        """
         help = action.help
-        if '%(default)' not in action.help:
+        if help is None:
+            help = ''
+
+        if '%(default)' not in help:
             if action.default is not SUPPRESS:
                 defaulting_nargs = [OPTIONAL, ZERO_OR_MORE]
                 if action.option_strings or action.nargs in defaulting_nargs:
@@ -704,6 +716,7 @@ class ArgumentDefaultsHelpFormatter(HelpFormatter):
         return help
 
 
+
 class MetavarTypeHelpFormatter(HelpFormatter):
     """Help message formatter which uses the argument 'type' as the default
     metavar value (instead of the argument 'dest')
@@ -719,7 +732,6 @@ class MetavarTypeHelpFormatter(HelpFormatter):
         return action.type.__name__
 
 
-
 # =====================
 # Options and Arguments
 # =====================
@@ -882,9 +894,6 @@ class BooleanOptionalAction(Action):
                 option_string = '--no-' + option_string[2:]
                 _option_strings.append(option_string)
 
-        if help is not None and default is not None and default is not SUPPRESS:
-            help += " (default: %(default)s)"
-
         super().__init__(
             option_strings=_option_strings,
             dest=dest,
@@ -896,6 +905,7 @@ class BooleanOptionalAction(Action):
             help=help,
             metavar=metavar)
 
+
     def __call__(self, parser, namespace, values, option_string=None):
         if option_string in self.option_strings:
             setattr(namespace, self.dest, not option_string.startswith('--no-'))