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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 fail(self):
 """Fail a vector."""

        if self.failed is True:
            raise AttributeError("Cannot fail {} - it has already failed.".format(self))
        else:
            self.failed = True
            self.time_of_death = timenow()

            for t in self.transmissions():
                t.fail()