Changed to use 'U' argument to PyArg_ParseTuple, instead of manually checking for unicode objects.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index c4fc57d..6675abf 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -293,7 +293,7 @@
                         goto done;
         }
 
-        if (!PyArg_ParseTuple(args, "O|O:format", &value, &spec))
+        if (!PyArg_ParseTuple(args, "O|U:format", &value, &spec))
                goto done;
 
         /* initialize the default value */