<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def observer_update(self, message):
 """Called when update from observer is received."""

        # Demultiplex observer update into multiple messages.
        for action in ('added', 'changed', 'removed'):
            for item in message[action]:
                self.send_json(
                    {
                        'msg': action,
                        'observer': message['observer'],
                        'primary_key': message['primary_key'],
                        'order': item['order'],
                        'item': item['data'],
                    }
                )