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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _command_callback(self, message):
 """ The callback subscribed to the broker """

        payload = message['payload']
        if message['$'] == 'before':
            self._commands.append({'level': self._depth,
                                   'payload': payload,
                                   'logs': []})
            self._depth += 1
        else:
            while not self._queue.empty():
                self._commands[-1]['logs'].append(self._queue.get())
            self._depth = max(self._depth-1, 0)