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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 allExpressionLevels(self):
 """ Return an iterator over all expression levels """

        for dataset in self.getDatasets():
            for rnaQuantificationSet in dataset.getRnaQuantificationSets():
                for rnaQuantification in \
                        rnaQuantificationSet.getRnaQuantifications():
                    for expressionLevel in \
                            rnaQuantification.getExpressionLevels():
                        yield expressionLevel