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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 advance_by(self, amount):
 """Advance the time reference by the given amount. :param `float` amount: number of seconds to advance. :raise `ValueError`: if *amount* is negative. """

        if amount < 0:
            raise ValueError("cannot retreat time reference: amount {} < 0"
                             .format(amount))
        self.__delta += amount