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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 successful(self):
 """Return True if the job finished with a COMPLETED status, False if it finished with a CANCELLED or FAILED status. Raise an `AssertionError` if the job has not completed"""

        status = self.status
        assert status >= COMPLETED, "status is %s" % status
        return (self.status == COMPLETED)