From d853d9a9aff3bb5b4c0f9e3acae9b2f6953a77b3 Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Sun, 12 Jun 2011 21:57:22 -0500
Subject: [PATCH] treat local as a black box

---
 _pytest/assertion/newinterpret.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/_pytest/assertion/newinterpret.py b/_pytest/assertion/newinterpret.py
index 992318470..6f5e59c94 100644
--- a/_pytest/assertion/newinterpret.py
+++ b/_pytest/assertion/newinterpret.py
@@ -152,8 +152,8 @@ class DebugInterpreter(ast.NodeVisitor):
             local = self.frame.eval(co)
         except Exception:
             # have to assume it isn't
-            local = False
-        if not self.frame.is_true(local):
+            local = None
+        if local is None or not self.frame.is_true(local):
             return name.id, result
         return explanation, result