better error output

Cython/Compiler/Visitor.py

@@ -46,7 +46,7 @@ class BasicVisitor(object):
                 if self.access_path:
                     print self.access_path[-1][0].pos
                     print self.access_path[-1][0].__dict__
-            raise RuntimeError("Visitor does not accept object: %s" % obj)
+            raise RuntimeError("Visitor %r does not accept object: %s" % (self, obj))
         #print "Caching " + cls.__name__
         return handler_method