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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 age(self, now=None):
 """ Returns an integer which is the difference in seconds from 'now' to when this circuit was created. Returns None if there is no created-time. """

        if not self.time_created:
            return None
        if now is None:
            now = datetime.utcnow()
        return (now - self.time_created).seconds