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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 prepare(self):
 """Un-serialize data from data attribute and add instance_id key if necessary :return: None """

        # Maybe the Brok is a old daemon one or was already prepared
        # if so, the data is already ok
        if hasattr(self, 'prepared') and not self.prepared:
            self.data = unserialize(self.data)
            if self.instance_id:
                self.data['instance_id'] = self.instance_id
        self.prepared = True