diff -r c5508c706293 Lib/argparse.py
--- a/Lib/argparse.py	Fri Jan 18 13:42:56 2013 +0100
+++ b/Lib/argparse.py	Fri Jan 18 10:46:00 2013 -0500
@@ -2293,7 +2293,7 @@
 
     def _check_value(self, action, value):
         # converted value must be one of the choices (if specified)
-        if action.choices is not None and value not in action.choices:
+        if action.choices is not None and value not in list(action.choices):
             args = {'value': value,
                     'choices': ', '.join(map(repr, action.choices))}
             msg = _('invalid choice: %(value)r (choose from %(choices)s)')