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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 _undo_save(self, datastreams, logMessage=None):
 """Takes a list of datastreams and a datetime, run undo save on all of them, and returns a list of the datastreams where the undo succeeded. :param datastreams: list of datastream ids (should be in self.dscache) :param logMessage: optional log message """

        return [ds for ds in datastreams if self.dscache[ds].undo_last_save(logMessage)]