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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 _addPredecessor(self, predecessorJob):
 """ Adds a predecessor job to the set of predecessor jobs. Raises a \ RuntimeError if the job is already a predecessor. """

        if predecessorJob in self._directPredecessors:
            raise RuntimeError("The given job is already a predecessor of this job")
        self._directPredecessors.add(predecessorJob)