def __init__(self, parent_message):
<EOL>if isinstance(parent_message, weakref.ProxyType):<EOL><INDENT>self._parent_message_weakref = parent_message<EOL><DEDENT>else:<EOL><INDENT>self._parent_message_weakref = weakref.proxy(parent_message)<EOL><DEDENT>self.dirty = False<EOL>
Args:
          parent_message: The message whose _Modified() method we should call when
            we receive Modified() messages.