Changed error message for StudentInputError for non-staff to

a generic message.  Otherwise, the default exception messages
are cryptic for students (e.g. "cannot convert string to float")

common/lib/xmodule/xmodule/capa_module.py

@@ -735,10 +735,10 @@ class CapaModule(CapaFields, XModule):
             if self.system.user_is_staff:
                 msg = traceback.format_exc()
 
-            # Otherwise, display just the error message,
+            # Otherwise, display just an error message,
             # without a stack trace
             else:
-                msg = inst.message
+                msg = "Error: Problem could not be evaluated with your input"
 
             return {'success': msg }
 

common/lib/xmodule/xmodule/tests/test_capa_module.py

@@ -516,11 +516,8 @@ class CapaModuleTest(unittest.TestCase):
             result = module.check_problem(get_request_dict)
 
             # Expect an AJAX alert message in 'success'
-            self.assertTrue('test error' in result['success'])
-
-            # We do NOT include traceback information for
-            # a non-staff user
-            self.assertFalse('Traceback' in result['success'])
+            expected_msg = 'Error: Problem could not be evaluated with your input'
+            self.assertEqual(expected_msg, result['success'])
 
         # Expect that the number of attempts is NOT incremented
         self.assertEqual(module.attempts, 1)