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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 cases(self):
 """ All test cases created by the user """

        import nitrate
        if self._cases is None:
            log.info(u"Searching for cases created by {0}".format(self.user))
            self._cases = [
                case for case in nitrate.TestCase.search(
                    author__email=self.user.email,
                    create_date__gt=str(self.options.since),
                    create_date__lt=str(self.options.until))
                if case.status != nitrate.CaseStatus("DISABLED")]
        return self._cases