bpo-45235: Fix argparse overrides namespace with subparser defaults (GH-28420)

1 files changed, 7 insertions, 6 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index d5a0afb..df98999 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1209,7 +1209,8 @@ class _SubParsersAction(Action):
         # namespace for the relevant parts.
         subnamespace, arg_strings = parser.parse_known_args(arg_strings, None)
         for key, value in vars(subnamespace).items():
-            setattr(namespace, key, value)
+            if not hasattr(namespace, key):
+                setattr(namespace, key, value)
 
         if arg_strings:
             vars(namespace).setdefault(_UNRECOGNIZED_ARGS_ATTR, [])
@@ -1843,11 +1844,6 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
                     if action.default is not SUPPRESS:
                         setattr(namespace, action.dest, action.default)
 
-        # add any parser defaults that aren't present
-        for dest in self._defaults:
-            if not hasattr(namespace, dest):
-                setattr(namespace, dest, self._defaults[dest])
-
         # parse the arguments and exit if there are any errors
         if self.exit_on_error:
             try:
@@ -1858,6 +1854,11 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         else:
             namespace, args = self._parse_known_args(args, namespace)
 
+        # add any parser defaults that aren't present
+        for dest in self._defaults:
+            if not hasattr(namespace, dest):
+                setattr(namespace, dest, self._defaults[dest])
+
         if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
             args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
             delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)