better error messages as discussed here:

http://codespeak.net/pipermail/py-dev/2009q2/001113.html

--HG--
branch : trunk

py/magic/exprinfo.py

@@ -428,9 +428,9 @@ def interpret(source, frame, should_fail=False):
         import traceback
         traceback.print_exc()
     if should_fail:
-        return ("(assert failed but re-evaluating the assert expression "
+        return ("(assertion failed, but when it was re-run for "
-                "for printing intermediate values lead to a True value. "
+                "printing intermediate values, it did not fail.  Suggestions: "
-                "advise: avoid side-effects in assert expressions or use --nomagic)")
+                "compute assert expression before the assert or use --nomagic)")
     else:
         return None
 

py/magic/testing/test_exprinfo.py

@@ -129,5 +129,5 @@ def test_inconsistent_assert_result(testdir):
     """)
     result = testdir.runpytest(p)
     s = result.stdout.str()
-    assert s.find("re-evaluating") 
+    assert s.find("re-run") != -1