argparse: Don't add default for required actions in DefaultsHelpFormatter

For actions with required=True, the ArgumentDefaultsHelpFormatter would always add a " (default: None)" to the end of the help text.
Since that's a bit misleading, it is removed with this commit.

Author: henzef

Lib/argparse.py

@@ -714,11 +714,15 @@ def _get_help_string(self, action):
         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:
-                    help += ' (default: %(default)s)'
+        if (
+            '%(default)' not in help
+            and action.default is not SUPPRESS
+            and not action.required
+        ):
+            defaulting_nargs = [OPTIONAL, ZERO_OR_MORE]
+            if action.option_strings or action.nargs in defaulting_nargs:
+                help += ' (default: %(default)s)'
+
         return help