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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 passport_series(self, year: int = None) -> str: """Generate random series of passport. :param year: Year of manufacture. :type year: int or None :return: Series. :Example: 02 15. """

        if not year:
            year = self.random.randint(10, 18)

        region = self.random.randint(1, 99)
        return '{:02d} {}'.format(region, year)