diff --git a/Lib/argparse.py b/Lib/argparse.py
index 2fb1da59f..9be18488a 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -392,6 +392,9 @@ class HelpFormatter(object):
         group_actions = set()
         inserts = {}
         for group in groups:
+            if not group._group_actions:
+                raise ValueError(f'empty group {group}')
+
             try:
                 start = actions.index(group._group_actions[0])
             except ValueError:
@@ -526,12 +529,13 @@ class HelpFormatter(object):
         parts = [action_header]
 
         # if there was help for the action, add lines of help text
-        if action.help:
+        if action.help and action.help.strip():
             help_text = self._expand_help(action)
-            help_lines = self._split_lines(help_text, help_width)
-            parts.append('%*s%s\n' % (indent_first, '', help_lines[0]))
-            for line in help_lines[1:]:
-                parts.append('%*s%s\n' % (help_position, '', line))
+            if help_text:
+                help_lines = self._split_lines(help_text, help_width)
+                parts.append('%*s%s\n' % (indent_first, '', help_lines[0]))
+                for line in help_lines[1:]:
+                    parts.append('%*s%s\n' % (help_position, '', line))
 
         # or add a newline if the description doesn't end with one
         elif not action_header.endswith('\n'):
@@ -722,11 +726,13 @@ def _get_action_name(argument):
     if argument is None:
         return None
     elif argument.option_strings:
-        return  '/'.join(argument.option_strings)
+        return '/'.join(argument.option_strings)
     elif argument.metavar not in (None, SUPPRESS):
         return argument.metavar
     elif argument.dest not in (None, SUPPRESS):
         return argument.dest
+    elif argument.choices:
+        return '{' + ','.join(argument.choices) + '}'
     else:
         return None
 
@@ -842,6 +848,7 @@ class Action(_AttributeHolder):
             'default',
             'type',
             'choices',
+            'required',
             'help',
             'metavar',
         ]
@@ -872,8 +879,8 @@ class BooleanOptionalAction(Action):
                 option_string = '--no-' + option_string[2:]
                 _option_strings.append(option_string)
 
-        if help is not None and default is not None:
-            help += f" (default: {default})"
+        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,
@@ -1250,9 +1257,9 @@ class FileType(object):
         # the special argument "-" means sys.std{in,out}
         if string == '-':
             if 'r' in self._mode:
-                return _sys.stdin
-            elif 'w' in self._mode:
-                return _sys.stdout
+                return _sys.stdin.buffer if 'b' in self._mode else _sys.stdin
+            elif any(c in self._mode for c in 'wax'):
+                return _sys.stdout.buffer if 'b' in self._mode else _sys.stdout
             else:
                 msg = _('argument "-" with mode %r') % self._mode
                 raise ValueError(msg)
@@ -1666,7 +1673,8 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
     """Object for parsing command line strings into Python objects.
 
     Keyword Arguments:
-        - prog -- The name of the program (default: sys.argv[0])
+        - prog -- The name of the program (default:
+            ``os.path.basename(sys.argv[0])``)
         - usage -- A usage message (default: auto-generated from arguments)
         - description -- A description of what the program does
         - epilog -- Text following the argument descriptions
@@ -1719,7 +1727,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
 
         add_group = self.add_argument_group
         self._positionals = add_group(_('positional arguments'))
-        self._optionals = add_group(_('optional arguments'))
+        self._optionals = add_group(_('options'))
         self._subparsers = None
 
         # register types