Fix tag

ccnode/tags.py

@@ -49,8 +49,8 @@ class Tag(object):
         self.watcher = None
 
     def calculate_value(self):
-        self._value = self._calculate_value()
-        # logger.debug('Calculate Tag(%s) = %s', self.name, self._value)
+        self.value = self._calculate_value()
+        # logger.debug('Calculate Tag(%s) = %s', self.name, self.value)
 
     def start(self, loop):
         """
@@ -60,7 +60,7 @@ class Tag(object):
             return
 
         if self.refresh is None:
-            self._value = self._calculate_value()
+            self.calculate_value()
             return
 
         # TODO more sophisticated calculation with event propagation