diff -r a1a1296556d7 Lib/argparse.py
--- a/Lib/argparse.py	Tue Apr 26 06:45:24 2011 +0300
+++ b/Lib/argparse.py	Wed Apr 27 18:14:34 2011 +0800
@@ -1590,8 +1590,9 @@
                  fromfile_prefix_chars=None,
                  argument_default=None,
                  conflict_handler='error',
-                 add_help=True):
-
+                 add_help=True,
+                 exit_on_argument_error=True):
+                 
         if version is not None:
             import warnings
             warnings.warn(
@@ -1617,6 +1618,7 @@
         self.formatter_class = formatter_class
         self.fromfile_prefix_chars = fromfile_prefix_chars
         self.add_help = add_help
+        self.exit_on_argument_error = exit_on_argument_error
 
         add_group = self.add_argument_group
         self._positionals = add_group(_('positional arguments'))
@@ -1754,15 +1756,19 @@
                 setattr(namespace, dest, self._defaults[dest])
 
         # parse the arguments and exit if there are any errors
-        try:
+        if not self.exit_on_argument_error:
             namespace, args = self._parse_known_args(args, namespace)
-            if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
-                args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
-                delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)
-            return namespace, args
-        except ArgumentError:
-            err = _sys.exc_info()[1]
-            self.error(str(err))
+        else:
+            try:
+                namespace, args = self._parse_known_args(args, namespace)
+            except ArgumentError:
+                err = _sys.exc_info()[1]
+                self.error(str(err))
+            
+        if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
+            args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
+            delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)
+        return namespace, args
 
     def _parse_known_args(self, arg_strings, namespace):
         # replace arg strings that are file references