def __repr__(self):
        return "<Requirement(package={package}, version='{version}')>".format(
            package=self.package, version=self.version)
def expiration_datetime(self):
        """Datetime that the verification will expire. """
        days_good_for = settings.VERIFY_STUDENT["DAYS_GOOD_FOR"]
        return self.created_at + timedelta(days=days_good_for)