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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 duration(self):
 """ Calculate how long the stage took. Returns: float: (current) duration of the stage """

        duration = 0.0
        if len(self.events) > 0:
            first = datetime.fromtimestamp(self.events[0]['timestamp'])
            last = datetime.fromtimestamp(self.events[-1]['timestamp'])
            duration = (last - first).total_seconds()
        return duration